下面以一个故事来讲来说明这中方式是怎么实现的。

放弃vlayout

大家都了解一般首页是非常复杂的，去年初项目引入vlayout来解决首页复杂布局的问题，后来对vlayout和databinding结合进行了封装，使用起来更方便简单，不仅首页使用，很多页面都在用，还封装了单纯列表样式的Activity，刷新加载的Activity，这样很开心的过了很久。由于vlayout项目一直比较活跃，在满足各种各样的需求上一直在打补丁，我也是一直在把它更新为最新版本，直到又一次更新我的的列表不显示内容了，经过一上午的排查，找到了问题。是在合并一个同学的PR时引入的，当时我还提了个issue 升级后出现onBindViewHolder未分发的问题，并给作者提了建议，加强Code Review，其实这时候我就没有那么happy了。

在一次需求中，PM提出了可以删除列表中某一条目的需求，在之前封装的基础上很简单就实现了。这时想加一个移除的动画吧，让APP活泼点，不是那么生硬。这可难住了我，一上午硬是没搞出来，在别的同学的issue 怎么正确的使用notifyItemRemoved，正是这个问题，使得我有了放弃使用vlayout的想法。不禁问自己，我为什么要使用它，没错就是为了使复杂布局更方便管理，现在看来有悖于初衷。也许vlayout有删除动画的简单实现方式，而我没有找到，但是我决定不再使用它。

寻找轮子

放弃之后面临的另一个问题是需求还是要做，项目还是要按时上线，冒出了第一个想法是找找其他的轮子吧，MultiItem github上的介绍是一个优雅的实现多类型的RecyclerView类库，窃喜，这不正是我想要的。他的思想是给BaseItemAdapter(设置给RecyclerView)注册一系列的Adapter，然后根据需要处理的类来区分是要选择哪个被代理的Adapter。

[java] view plain copy print ?

// 初始化adapter
BaseItemAdapter adapter = new BaseItemAdapter();
// 为TextBean数据源注册ViewHolderManager管理类
adapter.register(TextBean.class, new TextViewManager());
// 为更多数据源注册ViewHolderManager管理类
adapter.register(ImageTextBean.class, new ImageAndTextManager());
adapter.register(ImageBean.class, new ImageViewManager());
// 为RecyclerView设置Adapter
recyclerView.setAdapter(adapter);

// 初始化adapter
BaseItemAdapter adapter = new BaseItemAdapter();
// 为TextBean数据源注册ViewHolderManager管理类
adapter.register(TextBean.class, new TextViewManager());
// 为更多数据源注册ViewHolderManager管理类
adapter.register(ImageTextBean.class, new ImageAndTextManager());
adapter.register(ImageBean.class, new ImageViewManager());
// 为RecyclerView设置Adapter
recyclerView.setAdapter(adapter);

我要做的就是快速拿它匹配下我的场景，能不能满足我的需求。

是否支持多种类型条目？废话肯定支持；
是否支持不同条目不同数据类型？人家就是很久需要处理的数据类型来进行选择的，肯定没问题；
能不能支持一个数据类型对应多个样式？我看作者也是支持的，即通过数据实体中的标志来判断使用哪个Adapter；
能不能支持一个数据实体对应多个样式？由于是基于数据的类型进行选择代理Adapter的，这看来是无法实现。

我的微笑还没收场，就尴尬的定住了，5秒钟后，晃过神来，为什么我不按照这种思想自己封装一个。说实话我对作者的代理Adapter的管理还是不太满意的，这种思想很好，还是忍不住给作者点赞，那就自己来撸个轮子吧。

需求迭代

简单列表

PM在一次迭代过程中提出了要加一个新闻列表的需求，很简单，就是左边一个图片，右边一个标题、来源、发布时间，点击可以查看详情。

你一看，心中默念so easy，三下五除二，你就用RecyclerView很快实现了。

activity xml layout

[html] view plain copy print ?

<?xml version="1.0" encoding= "utf-8"?>
<android.support.constraint.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context="com.kevin.myapplication.MainActivity">
<android.support.v7.widget.RecyclerView
android:id="@+id/recycler_view"
android:layout_width="match_parent"
android:layout_height="match_parent"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintLeft_toLeftOf="parent"
app:layout_constraintRight_toRightOf="parent"
app:layout_constraintTop_toTopOf="parent" />
</android.support.constraint.ConstraintLayout>

<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context="com.kevin.myapplication.MainActivity">

    <android.support.v7.widget.RecyclerView
        android:id="@+id/recycler_view"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

</android.support.constraint.ConstraintLayout>

实体对象

[java] view plain copy print ?

public class News {
public String imgUrl = "";
public String content = "";
public String source = "";
public String time = "";
public String link = "";
}

public class News {
    public String imgUrl = "";
    public String content = "";
    public String source = "";
    public String time = "";
    public String link = "";
}

adapter

[java] view plain copy print ?

public class NewsAdapter extends RecyclerView.Adapter<NewsAdapter.ViewHolder> {
private List<News> dataItems = new ArrayList<>();
public void setDataItems(List<News> dataItems) {
this.dataItems = dataItems;
notifyDataSetChanged();
}
@Override
public ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.item_news, parent, false);
ViewHolder holder = new ViewHolder(view);
return holder;
}
@Override
public void onBindViewHolder(ViewHolder holder, int position) {
News news = dataItems.get(position);
holder.tvContent.setText(news.content);
holder.tvSource.setText(news.source);
holder.tvTime.setText(news.time);
Glide.with(holder.itemView.getContext()).load(news.imgUrl).into(holder.ivPic);
}
@Override
public int getItemCount() {
return dataItems.size();
}
static class ViewHolder extends RecyclerView.ViewHolder {
ImageView ivPic;
TextView tvContent;
TextView tvSource;
TextView tvTime;
public ViewHolder(View view) {
super(view);
ivPic = view.findViewById(R.id.iv_pic);
tvContent = view.findViewById(R.id.tv_content);
tvSource = view.findViewById(R.id.tv_source);
tvTime = view.findViewById(R.id.tv_time);
}
}
}

public class NewsAdapter extends RecyclerView.Adapter<NewsAdapter.ViewHolder> {

    private List<News> dataItems = new ArrayList<>();

    public void setDataItems(List<News> dataItems) {
        this.dataItems = dataItems;
        notifyDataSetChanged();
    }

    @Override
    public ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
        View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.item_news, parent, false);
        ViewHolder holder = new ViewHolder(view);
        return holder;
    }

    @Override
    public void onBindViewHolder(ViewHolder holder, int position) {
        News news = dataItems.get(position);
        holder.tvContent.setText(news.content);
        holder.tvSource.setText(news.source);
        holder.tvTime.setText(news.time);
        Glide.with(holder.itemView.getContext()).load(news.imgUrl).into(holder.ivPic);
    }

    @Override
    public int getItemCount() {
        return dataItems.size();
    }

    static class ViewHolder extends RecyclerView.ViewHolder {
        ImageView ivPic;
        TextView tvContent;
        TextView tvSource;
        TextView tvTime;

        public ViewHolder(View view) {
            super(view);
            ivPic = view.findViewById(R.id.iv_pic);
            tvContent = view.findViewById(R.id.tv_content);
            tvSource = view.findViewById(R.id.tv_source);
            tvTime = view.findViewById(R.id.tv_time);
        }
    }
}

adapter item layout

[java] view plain copy print ?

<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:paddingLeft="10dp"
android:paddingRight="10dp"
android:paddingTop="10dp">
<ImageView
android:id="@+id/iv_pic"
android:layout_width="0dp"
android:layout_height="80dp"
android:scaleType="centerCrop"
app:layout_constraintHorizontal_weight="1"
app:layout_constraintLeft_toLeftOf="parent"
app:layout_constraintRight_toLeftOf="@+id/tv_content"
app:layout_constraintTop_toTopOf="parent"
tools:src="@mipmap/ic_launcher" />
<TextView
android:id="@+id/tv_content"
android:layout_width="0dp"
android:layout_height="wrap_content"
android:layout_marginLeft="10dp"
android:ellipsize="end"
android:maxLines="2"
android:textColor="#333333"
android:textSize="18sp"
app:layout_constraintHorizontal_chainStyle="spread"
app:layout_constraintHorizontal_weight="2"
app:layout_constraintLeft_toRightOf="@+id/iv_pic"
app:layout_constraintRight_toRightOf="parent"
app:layout_constraintTop_toTopOf="parent"
tools:text="这是一条新闻，这是一条新闻，这是一条新闻" />
<TextView
android:id="@+id/tv_source"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginLeft="10dp"
android:textColor="#888888"
android:textSize="12sp"
app:layout_constraintBottom_toBottomOf="@+id/iv_pic"
app:layout_constraintLeft_toRightOf="@+id/iv_pic"
tools:text="澎湃新闻" />
<TextView
android:id="@+id/tv_time"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginLeft="8dp"
android:textColor="#888888"
android:textSize="12sp"
app:layout_constraintBottom_toBottomOf="@+id/iv_pic"
app:layout_constraintLeft_toRightOf="@+id/tv_source"
tools:text="07:33" />
<View
android:layout_width="0dp"
android:layout_height="1px"
android:layout_margin="10dp"
android:background="#EEEEEE"
app:layout_constraintTop_toBottomOf="@id/iv_pic" />
</android.support.constraint.ConstraintLayout>

<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:paddingLeft="10dp"
    android:paddingRight="10dp"
    android:paddingTop="10dp">

    <ImageView
        android:id="@+id/iv_pic"
        android:layout_width="0dp"
        android:layout_height="80dp"
        android:scaleType="centerCrop"
        app:layout_constraintHorizontal_weight="1"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toLeftOf="@+id/tv_content"
        app:layout_constraintTop_toTopOf="parent"
        tools:src="@mipmap/ic_launcher" />

    <TextView
        android:id="@+id/tv_content"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_marginLeft="10dp"
        android:ellipsize="end"
        android:maxLines="2"
        android:textColor="#333333"
        android:textSize="18sp"
        app:layout_constraintHorizontal_chainStyle="spread"
        app:layout_constraintHorizontal_weight="2"
        app:layout_constraintLeft_toRightOf="@+id/iv_pic"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        tools:text="这是一条新闻，这是一条新闻，这是一条新闻" />

    <TextView
        android:id="@+id/tv_source"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginLeft="10dp"
        android:textColor="#888888"
        android:textSize="12sp"
        app:layout_constraintBottom_toBottomOf="@+id/iv_pic"
        app:layout_constraintLeft_toRightOf="@+id/iv_pic"
        tools:text="澎湃新闻" />

    <TextView
        android:id="@+id/tv_time"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginLeft="8dp"
        android:textColor="#888888"
        android:textSize="12sp"
        app:layout_constraintBottom_toBottomOf="@+id/iv_pic"
        app:layout_constraintLeft_toRightOf="@+id/tv_source"
        tools:text="07:33" />

    <View
        android:layout_width="0dp"
        android:layout_height="1px"
        android:layout_margin="10dp"
        android:background="#EEEEEE"
        app:layout_constraintTop_toBottomOf="@id/iv_pic" />

</android.support.constraint.ConstraintLayout>

看一下实现，还不错的样子。

扩充样式

某天产品经理找到你说，只有一张图片的看着太单调了，能不能扩充出另外一种样式，一张图片的时候还是原来的样子，如果三张图片的时候上面是标题，下面是图片。你觉得没什么，也比较好实现，就没有做任何反抗去做了。

应该是这样，在之前一个图片的ViewHolder基础上扩展一个三个图片的ViewHoder，通过实体对象的图片数量进行区分是选择哪一个ViewHolder，不同的ViewHolder绑定不同的数据。

修改实体对象

把原来的String类型的图片数据改为List<String>的集合。

[java] view plain copy print ?

public class News {
public List<String> imgUrls = null;
public String content = "";
public String source = "";
public String time = "";
public String link = "";
}

public class News {
    public List<String> imgUrls = null;
    public String content = "";
    public String source = "";
    public String time = "";
    public String link = "";
}

新样式的xml layout

[html] view plain copy print ?

<?xml version="1.0" encoding= "utf-8"?>
<android.support.constraint.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:paddingLeft="10dp"
android:paddingRight="10dp"
android:paddingTop="10dp">
<TextView
android:id="@+id/tv_content"
android:layout_width="0dp"
android:layout_height="wrap_content"
android:ellipsize="end"
android:maxLines="2"
android:textColor="#333333"
android:textSize="18sp"
app:layout_constraintLeft_toLeftOf="parent"
app:layout_constraintRight_toRightOf="parent"
app:layout_constraintTop_toTopOf="parent"
tools:text="这是一条新闻，这是一条新闻，这是一条新闻" />
<ImageView
android:id="@+id/iv_pic1"
android:layout_width="0dp"
android:layout_height="80dp"
android:layout_marginTop="10dp"
android:scaleType="centerCrop"
app:layout_constraintHorizontal_weight="1"
app:layout_constraintLeft_toLeftOf="parent"
app:layout_constraintRight_toLeftOf="@+id/iv_pic2"
app:layout_constraintTop_toBottomOf="@+id/tv_content"
tools:src="@mipmap/ic_launcher" />
<ImageView
android:id="@+id/iv_pic2"
android:layout_width="0dp"
android:layout_height="80dp"
android:layout_marginLeft="4dp"
android:layout_marginTop="10dp"
android:scaleType="centerCrop"
app:layout_constraintHorizontal_weight="1"
app:layout_constraintLeft_toRightOf="@+id/iv_pic1"
app:layout_constraintRight_toLeftOf="@+id/iv_pic3"
app:layout_constraintTop_toBottomOf="@+id/tv_content"
tools:src="@mipmap/ic_launcher" />
<ImageView
android:id="@+id/iv_pic3"
android:layout_width="0dp"
android:layout_height="80dp"
android:layout_marginLeft="4dp"
android:layout_marginTop="10dp"
android:scaleType="centerCrop"
app:layout_constraintHorizontal_weight="1"
app:layout_constraintLeft_toRightOf="@+id/iv_pic2"
app:layout_constraintRight_toRightOf="parent"
app:layout_constraintTop_toBottomOf="@+id/tv_content"
tools:src="@mipmap/ic_launcher" />
<TextView
android:id="@+id/tv_source"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginTop="10dp"
android:textColor="#888888"
android:textSize="12sp"
app:layout_constraintLeft_toLeftOf="parent"
app:layout_constraintTop_toBottomOf="@+id/iv_pic1"
tools:text="澎湃新闻" />
<TextView
android:id="@+id/tv_time"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginLeft="8dp"
android:textColor="#888888"
android:textSize="12sp"
app:layout_constraintLeft_toRightOf="@+id/tv_source"
app:layout_constraintTop_toTopOf="@+id/tv_source"
tools:text="07:33" />
<View
android:layout_width="0dp"
android:layout_height="1px"
android:layout_margin="10dp"
android:background="#EEEEEE"
app:layout_constraintTop_toBottomOf="@id/tv_source" />
</android.support.constraint.ConstraintLayout>

<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:paddingLeft="10dp"
    android:paddingRight="10dp"
    android:paddingTop="10dp">

    <TextView
        android:id="@+id/tv_content"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:ellipsize="end"
        android:maxLines="2"
        android:textColor="#333333"
        android:textSize="18sp"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        tools:text="这是一条新闻，这是一条新闻，这是一条新闻" />

    <ImageView
        android:id="@+id/iv_pic1"
        android:layout_width="0dp"
        android:layout_height="80dp"
        android:layout_marginTop="10dp"
        android:scaleType="centerCrop"
        app:layout_constraintHorizontal_weight="1"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toLeftOf="@+id/iv_pic2"
        app:layout_constraintTop_toBottomOf="@+id/tv_content"
        tools:src="@mipmap/ic_launcher" />

    <ImageView
        android:id="@+id/iv_pic2"
        android:layout_width="0dp"
        android:layout_height="80dp"
        android:layout_marginLeft="4dp"
        android:layout_marginTop="10dp"
        android:scaleType="centerCrop"
        app:layout_constraintHorizontal_weight="1"
        app:layout_constraintLeft_toRightOf="@+id/iv_pic1"
        app:layout_constraintRight_toLeftOf="@+id/iv_pic3"
        app:layout_constraintTop_toBottomOf="@+id/tv_content"
        tools:src="@mipmap/ic_launcher" />

    <ImageView
        android:id="@+id/iv_pic3"
        android:layout_width="0dp"
        android:layout_height="80dp"
        android:layout_marginLeft="4dp"
        android:layout_marginTop="10dp"
        android:scaleType="centerCrop"
        app:layout_constraintHorizontal_weight="1"
        app:layout_constraintLeft_toRightOf="@+id/iv_pic2"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/tv_content"
        tools:src="@mipmap/ic_launcher" />

    <TextView
        android:id="@+id/tv_source"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginTop="10dp"
        android:textColor="#888888"
        android:textSize="12sp"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/iv_pic1"
        tools:text="澎湃新闻" />

    <TextView
        android:id="@+id/tv_time"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginLeft="8dp"
        android:textColor="#888888"
        android:textSize="12sp"
        app:layout_constraintLeft_toRightOf="@+id/tv_source"
        app:layout_constraintTop_toTopOf="@+id/tv_source"
        tools:text="07:33" />

    <View
        android:layout_width="0dp"
        android:layout_height="1px"
        android:layout_margin="10dp"
        android:background="#EEEEEE"
        app:layout_constraintTop_toBottomOf="@id/tv_source" />

</android.support.constraint.ConstraintLayout>

Adapter改造

复写getItemViewType方法，通过判断图片的个数是不是3个来区分样式。如果是则ViewType为1，如果不是则ViewType为0。

[java] view plain copy print ?

@Override
public int getItemViewType(int position) {
News news = dataItems.get(position);
boolean isThreePic = news.imgUrls.size() == 3;
int viewType = isThreePic ? 1 : 0;
return viewType;
}

@Override
public int getItemViewType(int position) {
    News news = dataItems.get(position);
    boolean isThreePic = news.imgUrls.size() == 3;
    int viewType = isThreePic ? 1 : 0;
    return viewType;
}

增加三张图片样式的ViewHolder

[java] view plain copy print ?

static class ThreePicViewHolder extends RecyclerView.ViewHolder {
ImageView ivPic1;
ImageView ivPic2;
ImageView ivPic3;
TextView tvContent;
TextView tvSource;
TextView tvTime;
public ThreePicViewHolder(View view) {
super(view);
ivPic1 = view.findViewById(R.id.iv_pic1);
ivPic2 = view.findViewById(R.id.iv_pic2);
ivPic3 = view.findViewById(R.id.iv_pic3);
tvContent = view.findViewById(R.id.tv_content);
tvSource = view.findViewById(R.id.tv_source);
tvTime = view.findViewById(R.id.tv_time);
}
}

static class ThreePicViewHolder extends RecyclerView.ViewHolder {
    ImageView ivPic1;
    ImageView ivPic2;
    ImageView ivPic3;
    TextView tvContent;
    TextView tvSource;
    TextView tvTime;

    public ThreePicViewHolder(View view) {
        super(view);
        ivPic1 = view.findViewById(R.id.iv_pic1);
        ivPic2 = view.findViewById(R.id.iv_pic2);
        ivPic3 = view.findViewById(R.id.iv_pic3);
        tvContent = view.findViewById(R.id.tv_content);
        tvSource = view.findViewById(R.id.tv_source);
        tvTime = view.findViewById(R.id.tv_time);
    }
}

在onCreateViewHolder中，通过判断ViewType的类型，创建对应的ViewHolder。

[java] view plain copy print ?

@Override
public RecyclerView.ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
if (viewType == 0) {
View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.item_news, parent, false);
OnePicViewHolder holder = new OnePicViewHolder(view);
return holder;
} else {
View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.item_news_extend, parent, false);
ThreePicViewHolder holder = new ThreePicViewHolder(view);
return holder;
}
}

@Override
public RecyclerView.ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
    if (viewType == 0) {
        View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.item_news, parent, false);
        OnePicViewHolder holder = new OnePicViewHolder(view);
        return holder;
    } else {
        View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.item_news_extend, parent, false);
        ThreePicViewHolder holder = new ThreePicViewHolder(view);
        return holder;
    }
}

在onBindingViewHolder中，通过判断ViewType的类型，绑定对应的数据到控件。

[java] view plain copy print ?

@Override
public void onBindViewHolder(RecyclerView.ViewHolder holder, int position) {
int viewType = holder.getItemViewType();
if (viewType == 0) {
OnePicViewHolder viewHolder = (OnePicViewHolder) holder;
News news = dataItems.get(position);
viewHolder.tvContent.setText(news.content);
viewHolder.tvSource.setText(news.source);
viewHolder.tvTime.setText(news.time);
Glide.with(holder.itemView.getContext()).load(news.imgUrls.get(0)).into(viewHolder.ivPic);
} else {
ThreePicViewHolder viewHolder = (ThreePicViewHolder) holder;
News news = dataItems.get(position);
viewHolder.tvContent.setText(news.content);
viewHolder.tvSource.setText(news.source);
viewHolder.tvTime.setText(news.time);
Glide.with(holder.itemView.getContext()).load(news.imgUrls.get(0)).into(viewHolder.ivPic1);
Glide.with(holder.itemView.getContext()).load(news.imgUrls.get(1)).into(viewHolder.ivPic2);
Glide.with(holder.itemView.getContext()).load(news.imgUrls.get(2)).into(viewHolder.ivPic3);
}
}

@Override
public void onBindViewHolder(RecyclerView.ViewHolder holder, int position) {
    int viewType = holder.getItemViewType();
    if (viewType == 0) {
        OnePicViewHolder viewHolder = (OnePicViewHolder) holder;
        News news = dataItems.get(position);
        viewHolder.tvContent.setText(news.content);
        viewHolder.tvSource.setText(news.source);
        viewHolder.tvTime.setText(news.time);
        Glide.with(holder.itemView.getContext()).load(news.imgUrls.get(0)).into(viewHolder.ivPic);
    } else {
        ThreePicViewHolder viewHolder = (ThreePicViewHolder) holder;
        News news = dataItems.get(position);
        viewHolder.tvContent.setText(news.content);
        viewHolder.tvSource.setText(news.source);
        viewHolder.tvTime.setText(news.time);
        Glide.with(holder.itemView.getContext()).load(news.imgUrls.get(0)).into(viewHolder.ivPic1);
        Glide.with(holder.itemView.getContext()).load(news.imgUrls.get(1)).into(viewHolder.ivPic2);
        Glide.with(holder.itemView.getContext()).load(news.imgUrls.get(2)).into(viewHolder.ivPic3);
    }
}

OK，很快就完成了，这次的需求，看了下效果，还可以。但是没有第一次那么开心了，隐隐感觉这里的代码有点恶心。

又扩充样式

过了一段时间，产品又找到你，说想增加一种图集类型的样式，上面是标题，下面是一张大图，点开是可以左右滑动翻页的图集。说完一张呆萌脸问你是不是很简单，你想到又要加一种类型的ViewHolder，而之前的实现已经让你不爽。你说：倒是不复杂，但是你也不能无限制的加啊。抱怨完了，还是要做的。

添加xml布局

[html] view plain copy print ?

<?xml version="1.0" encoding= "utf-8"?>
<android.support.constraint.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:paddingLeft="10dp"
android:paddingRight="10dp"
android:paddingTop="10dp">
<TextView
android:id="@+id/tv_content"
android:layout_width="0dp"
android:layout_height="wrap_content"
android:ellipsize="end"
android:maxLines="2"
android:textColor="#333333"
android:textSize="18sp"
app:layout_constraintLeft_toLeftOf="parent"
app:layout_constraintRight_toRightOf="parent"
app:layout_constraintTop_toTopOf="parent"
tools:text="这是一条新闻，这是一条新闻，这是一条新闻" />
<ImageView
android:id="@+id/iv_pic"
android:layout_width="0dp"
android:layout_height="0dp"
android:layout_marginTop="10dp"
android:scaleType="centerCrop"
app:layout_constraintDimensionRatio="5:3"
app:layout_constraintLeft_toLeftOf="parent"
app:layout_constraintRight_toRightOf="parent"
app:layout_constraintTop_toBottomOf="@+id/tv_content"
tools:src="@mipmap/ic_launcher" />
<TextView
android:id="@+id/tv_count"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:drawableLeft="@mipmap/icon_img"
android:drawablePadding="8dp"
android:paddingBottom="6dp"
android:paddingRight="10dp"
android:textColor="@android:color/white"
app:layout_constraintBottom_toBottomOf="@+id/iv_pic"
app:layout_constraintRight_toRightOf="@+id/iv_pic"
tools:text="图3" />
<TextView
android:id="@+id/tv_source"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginTop="10dp"
android:textColor="#888888"
android:textSize="12sp"
app:layout_constraintLeft_toLeftOf="parent"
app:layout_constraintTop_toBottomOf="@+id/iv_pic"
tools:text="澎湃新闻" />
<TextView
android:id="@+id/tv_time"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginLeft="8dp"
android:textColor="#888888"
android:textSize="12sp"
app:layout_constraintLeft_toRightOf="@+id/tv_source"
app:layout_constraintTop_toTopOf="@+id/tv_source"
tools:text="07:33" />
<View
android:layout_width="0dp"
android:layout_height="1px"
android:layout_margin="10dp"
android:background="#EEEEEE"
app:layout_constraintTop_toBottomOf="@id/tv_source" />
</android.support.constraint.ConstraintLayout>

<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:paddingLeft="10dp"
    android:paddingRight="10dp"
    android:paddingTop="10dp">

    <TextView
        android:id="@+id/tv_content"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:ellipsize="end"
        android:maxLines="2"
        android:textColor="#333333"
        android:textSize="18sp"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        tools:text="这是一条新闻，这是一条新闻，这是一条新闻" />

    <ImageView
        android:id="@+id/iv_pic"
        android:layout_width="0dp"
        android:layout_height="0dp"
        android:layout_marginTop="10dp"
        android:scaleType="centerCrop"
        app:layout_constraintDimensionRatio="5:3"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/tv_content"
        tools:src="@mipmap/ic_launcher" />

    <TextView
        android:id="@+id/tv_count"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:drawableLeft="@mipmap/icon_img"
        android:drawablePadding="8dp"
        android:paddingBottom="6dp"
        android:paddingRight="10dp"
        android:textColor="@android:color/white"
        app:layout_constraintBottom_toBottomOf="@+id/iv_pic"
        app:layout_constraintRight_toRightOf="@+id/iv_pic"
        tools:text="图3" />

    <TextView
        android:id="@+id/tv_source"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginTop="10dp"
        android:textColor="#888888"
        android:textSize="12sp"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/iv_pic"
        tools:text="澎湃新闻" />

    <TextView
        android:id="@+id/tv_time"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginLeft="8dp"
        android:textColor="#888888"
        android:textSize="12sp"
        app:layout_constraintLeft_toRightOf="@+id/tv_source"
        app:layout_constraintTop_toTopOf="@+id/tv_source"
        tools:text="07:33" />

    <View
        android:layout_width="0dp"
        android:layout_height="1px"
        android:layout_margin="10dp"
        android:background="#EEEEEE"
        app:layout_constraintTop_toBottomOf="@id/tv_source" />

</android.support.constraint.ConstraintLayout>

又改造Adapter

复写getItemViewType方法，通过判断图片的个数区分样式。

[java] view plain copy print ?

@Override
public int getItemViewType(int position) {
News news = dataItems.get(position);
int imgSize = news.imgUrls.size();
if (imgSize < 3) {
return 0;
} else if (imgSize == 3) {
return 2;
} else {
return 3;
}
}

@Override
public int getItemViewType(int position) {
    News news = dataItems.get(position);
    int imgSize = news.imgUrls.size();
    if (imgSize < 3) {
        return 0;
    } else if (imgSize == 3) {
        return 2;
    } else {
        return 3;
    }
}

增加图集样式的ViewHolder

[java] view plain copy print ?

static class MorePicViewHolder extends RecyclerView.ViewHolder {
ImageView ivPic;
TextView tvContent;
TextView tvCount;
TextView tvSource;
TextView tvTime;
public MorePicViewHolder(View view) {
super(view);
ivPic = view.findViewById(R.id.iv_pic);
tvContent = view.findViewById(R.id.tv_content);
tvCount = view.findViewById(R.id.tv_count);
tvSource = view.findViewById(R.id.tv_source);
tvTime = view.findViewById(R.id.tv_time);
}
}

static class MorePicViewHolder extends RecyclerView.ViewHolder {
    ImageView ivPic;
    TextView tvContent;
    TextView tvCount;
    TextView tvSource;
    TextView tvTime;

    public MorePicViewHolder(View view) {
        super(view);
        ivPic = view.findViewById(R.id.iv_pic);
        tvContent = view.findViewById(R.id.tv_content);
        tvCount = view.findViewById(R.id.tv_count);
        tvSource = view.findViewById(R.id.tv_source);
        tvTime = view.findViewById(R.id.tv_time);
    }
}

在onCreateViewHolder中，通过判断ViewType的类型，创建对应的ViewHolder。

[java] view plain copy print ?

@Override
public RecyclerView.ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
if (viewType == 0) {
View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.item_news_one_pic, parent, false);
OnePicViewHolder holder = new OnePicViewHolder(view);
return holder;
} else if (viewType == 2) {
View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.item_news_three_pic, parent, false);
ThreePicViewHolder holder = new ThreePicViewHolder(view);
return holder;
} else if (viewType == 3) {
View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.item_news_more_pic, parent, false);
MorePicViewHolder holder = new MorePicViewHolder(view);
return holder;
} else {
// Can't reach;
return null;
}
}

@Override
public RecyclerView.ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
    if (viewType == 0) {
        View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.item_news_one_pic, parent, false);
        OnePicViewHolder holder = new OnePicViewHolder(view);
        return holder;
    } else if (viewType == 2) {
        View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.item_news_three_pic, parent, false);
        ThreePicViewHolder holder = new ThreePicViewHolder(view);
        return holder;
    } else if (viewType == 3) {
        View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.item_news_more_pic, parent, false);
        MorePicViewHolder holder = new MorePicViewHolder(view);
        return holder;
    } else {
        // Can't reach;
        return null;
    }
}

在onBindingViewHolder中，通过判断ViewType的类型，绑定对应的数据到控件。

[java] view plain copy print ?

@Override
public void onBindViewHolder(RecyclerView.ViewHolder holder, int position) {
int viewType = holder.getItemViewType();
if (viewType == 0) {
OnePicViewHolder viewHolder = (OnePicViewHolder) holder;
News news = dataItems.get(position);
viewHolder.tvContent.setText(news.content);
viewHolder.tvSource.setText(news.source);
viewHolder.tvTime.setText(news.time);
Glide.with(holder.itemView.getContext()).load(news.imgUrls.get(0)).into(viewHolder.ivPic);
} else if (viewType == 2) {
ThreePicViewHolder viewHolder = (ThreePicViewHolder) holder;
News news = dataItems.get(position);
viewHolder.tvContent.setText(news.content);
viewHolder.tvSource.setText(news.source);
viewHolder.tvTime.setText(news.time);
Glide.with(holder.itemView.getContext()).load(news.imgUrls.get(0)).into(viewHolder.ivPic1);
Glide.with(holder.itemView.getContext()).load(news.imgUrls.get(1)).into(viewHolder.ivPic2);
Glide.with(holder.itemView.getContext()).load(news.imgUrls.get(2)).into(viewHolder.ivPic3);
} else if (viewType == 3) {
MorePicViewHolder viewHolder = (MorePicViewHolder) holder;
News news = dataItems.get(position);
viewHolder.tvContent.setText(news.content);
viewHolder.tvSource.setText(news.source);
viewHolder.tvTime.setText(news.time);
viewHolder.tvCount.setText(news.count + " 图");
Glide.with(holder.itemView.getContext()).load(news.imgUrls.get(0)).into(viewHolder.ivPic);
}
}

@Override
public void onBindViewHolder(RecyclerView.ViewHolder holder, int position) {
    int viewType = holder.getItemViewType();
    if (viewType == 0) {
        OnePicViewHolder viewHolder = (OnePicViewHolder) holder;
        News news = dataItems.get(position);
        viewHolder.tvContent.setText(news.content);
        viewHolder.tvSource.setText(news.source);
        viewHolder.tvTime.setText(news.time);
        Glide.with(holder.itemView.getContext()).load(news.imgUrls.get(0)).into(viewHolder.ivPic);
    } else if (viewType == 2) {
        ThreePicViewHolder viewHolder = (ThreePicViewHolder) holder;
        News news = dataItems.get(position);
        viewHolder.tvContent.setText(news.content);
        viewHolder.tvSource.setText(news.source);
        viewHolder.tvTime.setText(news.time);
        Glide.with(holder.itemView.getContext()).load(news.imgUrls.get(0)).into(viewHolder.ivPic1);
        Glide.with(holder.itemView.getContext()).load(news.imgUrls.get(1)).into(viewHolder.ivPic2);
        Glide.with(holder.itemView.getContext()).load(news.imgUrls.get(2)).into(viewHolder.ivPic3);
    } else if (viewType == 3) {
        MorePicViewHolder viewHolder = (MorePicViewHolder) holder;
        News news = dataItems.get(position);
        viewHolder.tvContent.setText(news.content);
        viewHolder.tvSource.setText(news.source);
        viewHolder.tvTime.setText(news.time);
        viewHolder.tvCount.setText(news.count + " 图");
        Glide.with(holder.itemView.getContext()).load(news.imgUrls.get(0)).into(viewHolder.ivPic);
    }
}

OK，很快又改完了，这次你的心情不太愉快，之前的太不利于扩展了，每次添加一种新的都要把Adapter改一遍。

反思

在上次需求上线之后，你开始反思，为什么我这么反感产品扩充样式，而不是我的代码有一定的业务兼容性，而是把自己搞的这么被动。算了，下楼喝杯咖啡冷静冷静。你顺便叫了下旁边的哥们，他说：“我比较忙，你给我带杯吧。”，“带什么？”你问，“摩卡小杯”。你心想，本来叫你一块儿去的，你小子这么懒叫我给你带。唉，对啊，我的Adapter不就可以这样嘛，自己不做处理，委托给其他的Adapter去做。

一开始的时候注册三个的委托Adapter对象，A委托Adapter可以处理一张图片的样式，B委托Adapter可以处理三张图片的样式，C委托可以处理多张图片的样式。根据数据里面图片的数量选择对应的委托Adapter去处理就可以啦。

委托

所有的委托都有相同的方法，为了方便定义一个接口。

[java] view plain copy print ?

public interface IDelegateAdapter {
// 查找委托时调用的方法，返回自己能处理的类型即可。
boolean isForViewType(News news);
// 用于委托Adapter的onCreateViewHolder方法
RecyclerView.ViewHolder onCreateViewHolder(ViewGroup parent, int viewType);
// 用于委托Adapter的onBindViewHolder方法
void onBindViewHolder(RecyclerView.ViewHolder holder, int position, News news);
}

public interface IDelegateAdapter {

    // 查找委托时调用的方法，返回自己能处理的类型即可。
    boolean isForViewType(News news);

    // 用于委托Adapter的onCreateViewHolder方法
    RecyclerView.ViewHolder onCreateViewHolder(ViewGroup parent, int viewType);

    // 用于委托Adapter的onBindViewHolder方法
    void onBindViewHolder(RecyclerView.ViewHolder holder, int position, News news);

}

然后是三个委托

[java] view plain copy print ?

public class OnePicDelegateAdapter implements IDelegateAdapter {
@Override
public boolean isForViewType(News news) {
// 我能处理一张图片
return news.imgUrls.size() == 1;
}
public RecyclerView.ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.item_news_one_pic, parent, false);
OnePicViewHolder holder = new OnePicViewHolder(view);
return holder;
}
public void onBindViewHolder(RecyclerView.ViewHolder holder, int position, News news) {
OnePicViewHolder viewHolder = (OnePicViewHolder) holder;
viewHolder.tvContent.setText(news.content);
viewHolder.tvSource.setText(news.source);
viewHolder.tvTime.setText(news.time);
Glide.with(holder.itemView.getContext()).load(news.imgUrls.get(0)).into(viewHolder.ivPic);
}
static class OnePicViewHolder extends RecyclerView.ViewHolder {
ImageView ivPic;
TextView tvContent;
TextView tvSource;
TextView tvTime;
public OnePicViewHolder(View view) {
super(view);
ivPic = view.findViewById(R.id.iv_pic);
tvContent = view.findViewById(R.id.tv_content);
tvSource = view.findViewById(R.id.tv_source);
tvTime = view.findViewById(R.id.tv_time);
}
}
}

public class OnePicDelegateAdapter implements IDelegateAdapter {

    @Override
    public boolean isForViewType(News news) {
        // 我能处理一张图片
        return news.imgUrls.size() == 1;
    }

    public RecyclerView.ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
        View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.item_news_one_pic, parent, false);
        OnePicViewHolder holder = new OnePicViewHolder(view);
        return holder;
    }

    public void onBindViewHolder(RecyclerView.ViewHolder holder, int position, News news) {
        OnePicViewHolder viewHolder = (OnePicViewHolder) holder;
        viewHolder.tvContent.setText(news.content);
        viewHolder.tvSource.setText(news.source);
        viewHolder.tvTime.setText(news.time);
        Glide.with(holder.itemView.getContext()).load(news.imgUrls.get(0)).into(viewHolder.ivPic);
    }

    static class OnePicViewHolder extends RecyclerView.ViewHolder {
        ImageView ivPic;
        TextView tvContent;
        TextView tvSource;
        TextView tvTime;

        public OnePicViewHolder(View view) {
            super(view);
            ivPic = view.findViewById(R.id.iv_pic);
            tvContent = view.findViewById(R.id.tv_content);
            tvSource = view.findViewById(R.id.tv_source);
            tvTime = view.findViewById(R.id.tv_time);
        }
    }
}

[java] view plain copy print ?

public class ThreePicDelegateAdapter implements IDelegateAdapter {
@Override
public boolean isForViewType(News news) {
// 我能处理三张图片
return news.imgUrls.size() == 3;
}
public RecyclerView.ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.item_news_three_pic, parent, false);
ThreePicViewHolder holder = new ThreePicViewHolder(view);
return holder;
}
public void onBindViewHolder(RecyclerView.ViewHolder holder, int position, News news) {
ThreePicViewHolder viewHolder = (ThreePicViewHolder) holder;
viewHolder.tvContent.setText(news.content);
viewHolder.tvSource.setText(news.source);
viewHolder.tvTime.setText(news.time);
Glide.with(holder.itemView.getContext()).load(news.imgUrls.get(0)).into(viewHolder.ivPic1);
Glide.with(holder.itemView.getContext()).load(news.imgUrls.get(1)).into(viewHolder.ivPic2);
Glide.with(holder.itemView.getContext()).load(news.imgUrls.get(2)).into(viewHolder.ivPic3);
}
static class ThreePicViewHolder extends RecyclerView.ViewHolder {
ImageView ivPic1;
ImageView ivPic2;
ImageView ivPic3;
TextView tvContent;
TextView tvSource;
TextView tvTime;
public ThreePicViewHolder(View view) {
super(view);
ivPic1 = view.findViewById(R.id.iv_pic1);
ivPic2 = view.findViewById(R.id.iv_pic2);
ivPic3 = view.findViewById(R.id.iv_pic3);
tvContent = view.findViewById(R.id.tv_content);
tvSource = view.findViewById(R.id.tv_source);
tvTime = view.findViewById(R.id.tv_time);
}
}
}

public class ThreePicDelegateAdapter implements IDelegateAdapter {

    @Override
    public boolean isForViewType(News news) {
        // 我能处理三张图片
        return news.imgUrls.size() == 3;
    }

    public RecyclerView.ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
        View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.item_news_three_pic, parent, false);
        ThreePicViewHolder holder = new ThreePicViewHolder(view);
        return holder;
    }

    public void onBindViewHolder(RecyclerView.ViewHolder holder, int position, News news) {
        ThreePicViewHolder viewHolder = (ThreePicViewHolder) holder;
        viewHolder.tvContent.setText(news.content);
        viewHolder.tvSource.setText(news.source);
        viewHolder.tvTime.setText(news.time);
        Glide.with(holder.itemView.getContext()).load(news.imgUrls.get(0)).into(viewHolder.ivPic1);
        Glide.with(holder.itemView.getContext()).load(news.imgUrls.get(1)).into(viewHolder.ivPic2);
        Glide.with(holder.itemView.getContext()).load(news.imgUrls.get(2)).into(viewHolder.ivPic3);
    }

    static class ThreePicViewHolder extends RecyclerView.ViewHolder {
        ImageView ivPic1;
        ImageView ivPic2;
        ImageView ivPic3;
        TextView tvContent;
        TextView tvSource;
        TextView tvTime;

        public ThreePicViewHolder(View view) {
            super(view);
            ivPic1 = view.findViewById(R.id.iv_pic1);
            ivPic2 = view.findViewById(R.id.iv_pic2);
            ivPic3 = view.findViewById(R.id.iv_pic3);
            tvContent = view.findViewById(R.id.tv_content);
            tvSource = view.findViewById(R.id.tv_source);
            tvTime = view.findViewById(R.id.tv_time);
        }
    }

}

[java] view plain copy print ?

public class MorePicDelegateAdapter implements IDelegateAdapter {
@Override
public boolean isForViewType(News news) {
// 我能处理多张图片
return news.imgUrls.size() > 3;
}
public RecyclerView.ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.item_news_more_pic, parent, false);
MorePicViewHolder holder = new MorePicViewHolder(view);
return holder;
}
public void onBindViewHolder(RecyclerView.ViewHolder holder, int position, News news) {
MorePicViewHolder viewHolder = (MorePicViewHolder) holder;
viewHolder.tvContent.setText(news.content);
viewHolder.tvSource.setText(news.source);
viewHolder.tvTime.setText(news.time);
viewHolder.tvCount.setText(news.count + " 图");
Glide.with(holder.itemView.getContext()).load(news.imgUrls.get(0)).into(viewHolder.ivPic);
}
static class MorePicViewHolder extends RecyclerView.ViewHolder {
ImageView ivPic;
TextView tvContent;
TextView tvCount;
TextView tvSource;
TextView tvTime;
public MorePicViewHolder(View view) {
super(view);
ivPic = view.findViewById(R.id.iv_pic);
tvContent = view.findViewById(R.id.tv_content);
tvCount = view.findViewById(R.id.tv_count);
tvSource = view.findViewById(R.id.tv_source);
tvTime = view.findViewById(R.id.tv_time);
}
}
}

public class MorePicDelegateAdapter implements IDelegateAdapter {

    @Override
    public boolean isForViewType(News news) {
        // 我能处理多张图片
        return news.imgUrls.size() > 3;
    }

    public RecyclerView.ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
        View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.item_news_more_pic, parent, false);
        MorePicViewHolder holder = new MorePicViewHolder(view);
        return holder;
    }

    public void onBindViewHolder(RecyclerView.ViewHolder holder, int position, News news) {
        MorePicViewHolder viewHolder = (MorePicViewHolder) holder;
        viewHolder.tvContent.setText(news.content);
        viewHolder.tvSource.setText(news.source);
        viewHolder.tvTime.setText(news.time);
        viewHolder.tvCount.setText(news.count + " 图");
        Glide.with(holder.itemView.getContext()).load(news.imgUrls.get(0)).into(viewHolder.ivPic);
    }

    static class MorePicViewHolder extends RecyclerView.ViewHolder {
        ImageView ivPic;
        TextView tvContent;
        TextView tvCount;
        TextView tvSource;
        TextView tvTime;

        public MorePicViewHolder(View view) {
            super(view);
            ivPic = view.findViewById(R.id.iv_pic);
            tvContent = view.findViewById(R.id.tv_content);
            tvCount = view.findViewById(R.id.tv_count);
            tvSource = view.findViewById(R.id.tv_source);
            tvTime = view.findViewById(R.id.tv_time);
        }
    }

}

再看下之前冗余的Adapter，现在已经非常清瘦了

[java] view plain copy print ?

public class NewsAdapter extends RecyclerView.Adapter<RecyclerView.ViewHolder> {
private List<News> dataItems = new ArrayList<>();
public void setDataItems(List<News> dataItems) {
this.dataItems = dataItems;
notifyDataSetChanged();
}
List<IDelegateAdapter> delegateAdapters = new ArrayList<>();
public void addDelegate(IDelegateAdapter delegateAdapter) {
delegateAdapters.add(delegateAdapter);
}
@Override
public int getItemViewType(int position) {
}
@Override
public RecyclerView.ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
}
@Override
public void onBindViewHolder(RecyclerView.ViewHolder holder, int position) {
}
@Override
public int getItemCount() {
return dataItems.size();
}
}

public class NewsAdapter extends RecyclerView.Adapter<RecyclerView.ViewHolder> {

    private List<News> dataItems = new ArrayList<>();

    public void setDataItems(List<News> dataItems) {
        this.dataItems = dataItems;
        notifyDataSetChanged();
    }

    List<IDelegateAdapter> delegateAdapters = new ArrayList<>();

    public void addDelegate(IDelegateAdapter delegateAdapter) {
        delegateAdapters.add(delegateAdapter);
    }

    @Override
    public int getItemViewType(int position) {

    }

    @Override
    public RecyclerView.ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {

    }

    @Override
    public void onBindViewHolder(RecyclerView.ViewHolder holder, int position) {

    }

    @Override
    public int getItemCount() {
        return dataItems.size();
    }

}

有三个方法需要我们去填空，在之前的图中我们说过，getItemViewType通过委托在集合中的index去标识。

[java] view plain copy print ?

@Override
public int getItemViewType(int position) {
// 找到当前位置的数据
News news = dataItems.get(position);
// 遍历所有的代理，问下他们谁能处理
for (IDelegateAdapter delegateAdapter : delegateAdapters) {
if (delegateAdapter.isForViewType(news)) {
// 谁能处理返回他的index
return delegateAdapters.indexOf(delegateAdapter);
}
}
throw new RuntimeException("没有找到可以处理的委托Adapter");
}

@Override
public int getItemViewType(int position) {
    // 找到当前位置的数据
    News news = dataItems.get(position);

    // 遍历所有的代理，问下他们谁能处理
    for (IDelegateAdapter delegateAdapter : delegateAdapters) {
        if (delegateAdapter.isForViewType(news)) {
            // 谁能处理返回他的index
            return delegateAdapters.indexOf(delegateAdapter);
        }
    }

    throw new RuntimeException("没有找到可以处理的委托Adapter");
}

然后是onCreateViewHolder，既然是通过委托Adapter的在集合中的index去标记的ViewType，那么在onCreateViewHolder中就非常简单了。

[java] view plain copy print ?

@Override
public RecyclerView.ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
// 找到对应的委托Adapter
IDelegateAdapter delegateAdapter = delegateAdapters.get(viewType);
// 把onCreateViewHolder交给委托Adapter去处理
RecyclerView.ViewHolder viewHolder = delegateAdapter.onCreateViewHolder(parent, viewType);
return viewHolder;
}

@Override
public RecyclerView.ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
    // 找到对应的委托Adapter
    IDelegateAdapter delegateAdapter = delegateAdapters.get(viewType);
    // 把onCreateViewHolder交给委托Adapter去处理
    RecyclerView.ViewHolder viewHolder = delegateAdapter.onCreateViewHolder(parent, viewType);
    return viewHolder;
}

接下来是onBindViewHolder，类似onCreateViewHolder，这里也是找到委托Adapter，交给他去处理。

[java] view plain copy print ?

@Override
public void onBindViewHolder(RecyclerView.ViewHolder holder, int position) {
// 找到当前ViewHolder的ViewType，也就是委托Adapter在集合中的index
int viewType = holder.getItemViewType();
// 找到对应的委托Adapter
IDelegateAdapter delegateAdapter = delegateAdapters.get(viewType);
// 把onBindViewHolder交给委托Adapter去处理
delegateAdapter.onBindViewHolder(holder, position, dataItems.get(position));
}

@Override
public void onBindViewHolder(RecyclerView.ViewHolder holder, int position) {
    // 找到当前ViewHolder的ViewType，也就是委托Adapter在集合中的index
    int viewType = holder.getItemViewType();
    // 找到对应的委托Adapter
    IDelegateAdapter delegateAdapter = delegateAdapters.get(viewType);
    // 把onBindViewHolder交给委托Adapter去处理
    delegateAdapter.onBindViewHolder(holder, position, dataItems.get(position));
}

使用的时候也非常简单，在之前的基础上注册委托Adapter就可以了。

[java] view plain copy print ?

RecyclerView recyclerView = findViewById(R.id.recycler_view);
LinearLayoutManager layoutManager = new LinearLayoutManager(this);
recyclerView.setLayoutManager(layoutManager);
NewsAdapter mAdapter = new NewsAdapter();
// 添加委托Adapter
mAdapter.addDelegate(new OnePicDelegateAdapter());
mAdapter.addDelegate(new ThreePicDelegateAdapter());
mAdapter.addDelegate(new MorePicDelegateAdapter());
recyclerView.setAdapter(mAdapter);

RecyclerView recyclerView = findViewById(R.id.recycler_view);
LinearLayoutManager layoutManager = new LinearLayoutManager(this);
recyclerView.setLayoutManager(layoutManager);
NewsAdapter mAdapter = new NewsAdapter();
// 添加委托Adapter
mAdapter.addDelegate(new OnePicDelegateAdapter());
mAdapter.addDelegate(new ThreePicDelegateAdapter());
mAdapter.addDelegate(new MorePicDelegateAdapter());

recyclerView.setAdapter(mAdapter);

双扩充样式

产品经理又来了，说又要添加一种视频类型的样式。你爽快地说：“没问题”。

之前一直是通过图片的个数来判断是那种形式，但这次明显不能这么干了，修改原来的实体，添加一个type来标识是那种类型。

[java] view plain copy print ?

public class News {
public int type = 0; // 0:一张图片；1:三张图片；2:多张图片；3:视频类型
public List<String> imgUrls = null;
public String content = "";
public String count = "";
public String duration = "";
public String source = "";
public String time = "";
public String link = "";
}

public class News {
    public int type = 0; // 0:一张图片；1:三张图片；2:多张图片；3:视频类型
    public List<String> imgUrls = null;
    public String content = "";
    public String count = "";
    public String duration = "";
    public String source = "";
    public String time = "";
    public String link = "";
}

添加xml布局

[html] view plain copy print ?

<?xml version="1.0" encoding= "utf-8"?>
<android.support.constraint.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:paddingLeft="10dp"
android:paddingRight="10dp"
android:paddingTop="10dp">
<TextView
android:id="@+id/tv_content"
android:layout_width="0dp"
android:layout_height="wrap_content"
android:ellipsize="end"
android:maxLines="2"
android:textColor="#333333"
android:textSize="18sp"
app:layout_constraintLeft_toLeftOf="parent"
app:layout_constraintRight_toRightOf="parent"
app:layout_constraintTop_toTopOf="parent"
tools:text="这是一条新闻，这是一条新闻，这是一条新闻" />
<ImageView
android:id="@+id/iv_pic"
android:layout_width="0dp"
android:layout_height="0dp"
android:layout_marginTop="10dp"
android:scaleType="centerCrop"
app:layout_constraintDimensionRatio="5:3"
app:layout_constraintLeft_toLeftOf="parent"
app:layout_constraintRight_toRightOf="parent"
app:layout_constraintTop_toBottomOf="@+id/tv_content"
tools:src="@mipmap/ic_launcher" />
<ImageView
android:layout_width="48dp"
android:layout_height="48dp"
android:src="@mipmap/play90"
app:layout_constraintBottom_toBottomOf="@+id/iv_pic"
app:layout_constraintLeft_toLeftOf="@+id/iv_pic"
app:layout_constraintRight_toRightOf="@+id/iv_pic"
app:layout_constraintTop_toTopOf="@+id/iv_pic" />
<TextView
android:id="@+id/tv_duration"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:paddingBottom="6dp"
android:paddingRight="10dp"
android:textColor="@android:color/white"
app:layout_constraintBottom_toBottomOf="@+id/iv_pic"
app:layout_constraintRight_toRightOf="@+id/iv_pic"
tools:text="12:34" />
<TextView
android:id="@+id/tv_source"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginTop="10dp"
android:textColor="#888888"
android:textSize="12sp"
app:layout_constraintLeft_toLeftOf="parent"
app:layout_constraintTop_toBottomOf="@+id/iv_pic"
tools:text="澎湃新闻" />
<TextView
android:id="@+id/tv_time"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginLeft="8dp"
android:textColor="#888888"
android:textSize="12sp"
app:layout_constraintLeft_toRightOf="@+id/tv_source"
app:layout_constraintTop_toTopOf="@+id/tv_source"
tools:text="07:33" />
<View
android:layout_width="0dp"
android:layout_height="1px"
android:layout_margin="10dp"
android:background="#EEEEEE"
app:layout_constraintTop_toBottomOf="@id/tv_source" />
</android.support.constraint.ConstraintLayout>

<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:paddingLeft="10dp"
    android:paddingRight="10dp"
    android:paddingTop="10dp">

    <TextView
        android:id="@+id/tv_content"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:ellipsize="end"
        android:maxLines="2"
        android:textColor="#333333"
        android:textSize="18sp"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        tools:text="这是一条新闻，这是一条新闻，这是一条新闻" />

    <ImageView
        android:id="@+id/iv_pic"
        android:layout_width="0dp"
        android:layout_height="0dp"
        android:layout_marginTop="10dp"
        android:scaleType="centerCrop"
        app:layout_constraintDimensionRatio="5:3"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/tv_content"
        tools:src="@mipmap/ic_launcher" />

    <ImageView
        android:layout_width="48dp"
        android:layout_height="48dp"
        android:src="@mipmap/play90"
        app:layout_constraintBottom_toBottomOf="@+id/iv_pic"
        app:layout_constraintLeft_toLeftOf="@+id/iv_pic"
        app:layout_constraintRight_toRightOf="@+id/iv_pic"
        app:layout_constraintTop_toTopOf="@+id/iv_pic" />

    <TextView
        android:id="@+id/tv_duration"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:paddingBottom="6dp"
        android:paddingRight="10dp"
        android:textColor="@android:color/white"
        app:layout_constraintBottom_toBottomOf="@+id/iv_pic"
        app:layout_constraintRight_toRightOf="@+id/iv_pic"
        tools:text="12:34" />

    <TextView
        android:id="@+id/tv_source"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginTop="10dp"
        android:textColor="#888888"
        android:textSize="12sp"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/iv_pic"
        tools:text="澎湃新闻" />

    <TextView
        android:id="@+id/tv_time"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginLeft="8dp"
        android:textColor="#888888"
        android:textSize="12sp"
        app:layout_constraintLeft_toRightOf="@+id/tv_source"
        app:layout_constraintTop_toTopOf="@+id/tv_source"
        tools:text="07:33" />

    <View
        android:layout_width="0dp"
        android:layout_height="1px"
        android:layout_margin="10dp"
        android:background="#EEEEEE"
        app:layout_constraintTop_toBottomOf="@id/tv_source" />

</android.support.constraint.ConstraintLayout>

添加委托Adapter

[java] view plain copy print ?

public class VideoDelegateAdapter implements IDelegateAdapter {
@Override
public boolean isForViewType(News news) {
// 我能处理视频类型
return news.type == 3;
}
public RecyclerView.ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.item_news_video, parent, false);
VideoViewHolder holder = new VideoViewHolder(view);
return holder;
}
public void onBindViewHolder(RecyclerView.ViewHolder holder, int position, News news) {
VideoViewHolder viewHolder = (VideoViewHolder) holder;
viewHolder.tvContent.setText(news.content);
viewHolder.tvSource.setText(news.source);
viewHolder.tvTime.setText(news.time);
viewHolder.tvDuration.setText(news.duration);
Glide.with(holder.itemView.getContext()).load(news.imgUrls.get(0)).into(viewHolder.ivPic);
}
static class VideoViewHolder extends RecyclerView.ViewHolder {
ImageView ivPic;
TextView tvContent;
TextView tvDuration;
TextView tvSource;
TextView tvTime;
public VideoViewHolder(View view) {
super(view);
ivPic = view.findViewById(R.id.iv_pic);
tvContent = view.findViewById(R.id.tv_content);
tvDuration = view.findViewById(R.id.tv_duration);
tvSource = view.findViewById(R.id.tv_source);
tvTime = view.findViewById(R.id.tv_time);
}
}
}

public class VideoDelegateAdapter implements IDelegateAdapter {

    @Override
    public boolean isForViewType(News news) {
        // 我能处理视频类型
        return news.type == 3;
    }

    public RecyclerView.ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
        View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.item_news_video, parent, false);
        VideoViewHolder holder = new VideoViewHolder(view);
        return holder;
    }

    public void onBindViewHolder(RecyclerView.ViewHolder holder, int position, News news) {
        VideoViewHolder viewHolder = (VideoViewHolder) holder;
        viewHolder.tvContent.setText(news.content);
        viewHolder.tvSource.setText(news.source);
        viewHolder.tvTime.setText(news.time);
        viewHolder.tvDuration.setText(news.duration);
        Glide.with(holder.itemView.getContext()).load(news.imgUrls.get(0)).into(viewHolder.ivPic);
    }

    static class VideoViewHolder extends RecyclerView.ViewHolder {
        ImageView ivPic;
        TextView tvContent;
        TextView tvDuration;
        TextView tvSource;
        TextView tvTime;

        public VideoViewHolder(View view) {
            super(view);
            ivPic = view.findViewById(R.id.iv_pic);
            tvContent = view.findViewById(R.id.tv_content);
            tvDuration = view.findViewById(R.id.tv_duration);
            tvSource = view.findViewById(R.id.tv_source);
            tvTime = view.findViewById(R.id.tv_time);
        }
    }

}

添加注册委托代理

[java] view plain copy print ?

// 添加委托Adapter
mAdapter.addDelegate(new OnePicDelegateAdapter());
mAdapter.addDelegate(new ThreePicDelegateAdapter());
mAdapter.addDelegate(new MorePicDelegateAdapter());
mAdapter.addDelegate(new VideoDelegateAdapter()); // 新添加的视频类型

// 添加委托Adapter
mAdapter.addDelegate(new OnePicDelegateAdapter());
mAdapter.addDelegate(new ThreePicDelegateAdapter());
mAdapter.addDelegate(new MorePicDelegateAdapter());
mAdapter.addDelegate(new VideoDelegateAdapter()); // 新添加的视频类型

经过非常简单的三步之后，就很清爽地完成了这次需求，大家都很开心。

叒扩充样式

产品经理再一次找到你，说我们的新闻很火爆，希望加入广告。每10条加入一个广告，是不是很好做。你心想，卧槽，这他么不是坑我么。没办法，产品经理的性子你也知道，这个肯定是要做的。

这么看来之前的封装还是不能满足的，之前的是要求所有的数据都有相同的类型。那能不能加入不同数据类型的支持呢？

看下之前的是通过一个List来保存托管Adapter的，这样是无法保存不同的类型信息的。

[java] view plain copy print ?

List<IDelegateAdapter> delegateAdapters = new ArrayList<>();

List<IDelegateAdapter> delegateAdapters = new ArrayList<>();

那就再增加一个保存类型信息的List吧，为了便于查找，这里使用Android提供的SparseArrayCompat。两个集合定义如下：

[java] view plain copy print ?

// 用于保存委托Adapter
private SparseArrayCompat<AdapterDelegate<Object>> delegates = new SparseArrayCompat();
// 用于保存委托Adapter能处理的类型
private SparseArray<String> dataTypes = new SparseArray<>();

// 用于保存委托Adapter
private SparseArrayCompat<AdapterDelegate<Object>> delegates = new SparseArrayCompat();
// 用于保存委托Adapter能处理的类型
private SparseArray<String> dataTypes = new SparseArray<>();

[java] view plain copy print ?

public AdapterDelegatesManager addDelegate(AdapterDelegate<Object, VH> delegate) {
Type superclass = delegate.getClass().getGenericSuperclass();
if (superclass instanceof ParameterizedType) {
Class<?> clazz = (Class<?>) ((ParameterizedType) superclass).getActualTypeArguments()[0];
String typeWithTag = clazz.getName();
int viewType = delegates.size();
// Save the delegate to the collection;
delegates.put(viewType, delegate);
// Save the index of the delegate to the collection;
dataTypes.put(viewType, typeWithTag);
} else {
// Has no generics.
throw new IllegalArgumentException(
String.format("Please set the correct generic parameters on %s.", delegate.getClass().getName()));
}
return this;
}

public AdapterDelegatesManager addDelegate(AdapterDelegate<Object, VH> delegate) {
    Type superclass = delegate.getClass().getGenericSuperclass();
    if (superclass instanceof ParameterizedType) {
        Class<?> clazz = (Class<?>) ((ParameterizedType) superclass).getActualTypeArguments()[0];
        String typeWithTag = clazz.getName();

        int viewType = delegates.size();
        // Save the delegate to the collection;
        delegates.put(viewType, delegate);
        // Save the index of the delegate to the collection;
        dataTypes.put(viewType, typeWithTag);
    } else {
        // Has no generics.
        throw new IllegalArgumentException(
                String.format("Please set the correct generic parameters on %s.", delegate.getClass().getName()));
    }
    return this;
}

每向delegates中添加一个委托Adapter，则向dataTypes中添加该委托Adapter能处理的类型。比如：向delegates添加一个能处理String类型的委托 AdapterDelegate<String>位置是1，那么向dataType中添加一个java.lang.String位置也是1。那么在处理String类型的数据的时候在dataType中查找到对应的位置为1，就可以去delegate的1位置取对应的委托Adapter就可以啦。

这里就不再贴代码了，github地址DelegationAdapter。

叕来需求

经过以上封装，你开心地工作了相当长的一段时间。有一天产品又找到你，我们要做一个账单详情页，很简单，就是显示他的消费信息。

你一看，上面是固定的信息，下面是固定的信息，中间是一个列表。使用ListView的添加头部、尾部会非常简单，但是你又不想使用ListView。能不能使用封装的RecyclerView委托Adapter实现呢？

[java] view plain copy print ?

public class Bill {
public String title = ""; // 标题
public String waiter = ""; // 服务员
public String cashier = ""; // 收银员
public int ramadhin = 0; // 桌号
public int guests = 0; // 客人数
public String beginTime = ""; // 开台时间
public String endTime = ""; // 结账时间
public String duration = ""; // 用餐时长
public List<Item> details = null; // 用餐详情
public String total = ""; // 合计
public String discounts = ""; // 优惠
public String receivable = ""; // 应收
public String describe = ""; // 描述信息
public static class Item {
public String name = ""; // 名称
public String count = ""; // 数量
public String price = ""; // 单价
public String subtotal = "";// 小计
}
}

public class Bill {

    public String title = "";           // 标题
    public String waiter = "";          // 服务员
    public String cashier = "";         // 收银员
    public int ramadhin = 0;            // 桌号
    public int guests = 0;              // 客人数
    public String beginTime = "";       // 开台时间
    public String endTime = "";         // 结账时间
    public String duration = "";        // 用餐时长
    public List<Item> details = null;   // 用餐详情
    public String total = "";           // 合计
    public String discounts = "";       // 优惠
    public String receivable = "";      // 应收
    public String describe = "";        // 描述信息

    public static class Item {
        public String name = "";    // 名称
        public String count = "";   // 数量
        public String price = "";   // 单价
        public String subtotal = "";// 小计
    }

}

通过分析，应该是三个委托Adapter，即上中下三部分。中间部分还好，类型是Bill.Item，但是上下两部分就无法区分了，都是Bill类型。

那怎样才能区分相同数据类型同一数据的委托Adapter呢？能不能给每个委托Adapter打一个Tag，在设置数据的时候也添加Tag，这样就可以通过Tag去区分了。修改设置数据类型标记的部分。

[java] view plain copy print ?

// 用于保存委托Adapter
private SparseArrayCompat<AdapterDelegate<Object, VH>> delegates = new SparseArrayCompat();
// 用于保存委托Adapter能处理的类型
private SparseArray<String> dataTypeWithTags = new SparseArray<>();

// 用于保存委托Adapter
private SparseArrayCompat<AdapterDelegate<Object, VH>> delegates = new SparseArrayCompat();
// 用于保存委托Adapter能处理的类型
private SparseArray<String> dataTypeWithTags = new SparseArray<>();

[java] view plain copy print ?

public AdapterDelegatesManager addDelegate(AdapterDelegate<Object, VH> delegate, String tag) {
Type superclass = delegate.getClass().getGenericSuperclass();
if (superclass instanceof ParameterizedType) {
Class<?> clazz = (Class<?>) ((ParameterizedType) superclass).getActualTypeArguments()[0];
String typeWithTag = clazz.getName() + ":" + tag;
int viewType = delegates.size();
// Save the delegate to the collection;
delegates.put(viewType, delegate);
// Save the index of the delegate to the collection;
dataTypeWithTags.put(viewType, typeWithTag);
} else {
// Has no generics.
throw new IllegalArgumentException(
String.format("Please set the correct generic parameters on %s.", delegate.getClass().getName()));
}
return this;
}

public AdapterDelegatesManager addDelegate(AdapterDelegate<Object, VH> delegate, String tag) {
    Type superclass = delegate.getClass().getGenericSuperclass();
    if (superclass instanceof ParameterizedType) {
        Class<?> clazz = (Class<?>) ((ParameterizedType) superclass).getActualTypeArguments()[0];
        String typeWithTag = clazz.getName() + ":" + tag;

        int viewType = delegates.size();
        // Save the delegate to the collection;
        delegates.put(viewType, delegate);
        // Save the index of the delegate to the collection;
        dataTypeWithTags.put(viewType, typeWithTag);
    } else {
        // Has no generics.
        throw new IllegalArgumentException(
                String.format("Please set the correct generic parameters on %s.", delegate.getClass().getName()));
    }
    return this;
}

通过一个动画来总结下实现方案，开始注册了四个委托Adapter，其中A、C类型都为String，通过tag标记来区分；添加数据之后，RecyclerView进行布局，首先处理带tag为A的字符串"ABCDEF"，那么到委托集合中去找对应的Adapter去进行渲染。接着一个个都完成了渲染。

OK，很轻松就搞定了。剩余代码及详细demo请移步github DelegationAdapter。

以后终于能开心地撸码了。

一种优雅的方式实现RecyclerView条目多类型

放弃vlayout

寻找轮子

需求迭代

简单列表

activity xml layout

adapter

adapter item layout

扩充样式

修改实体对象

新样式的xml layout

Adapter改造

又扩充样式

添加xml布局

又改造Adapter

反思

委托

双扩充样式

叒扩充样式

叕来需求