为 RecyclerView 设置可推动的悬浮导航栏 ---ItemDecorationd 的使用（三）

开始逐渐领略到ItemDecoration的美~

今天让我使用 ItemDecoration 来完成可推动的悬浮导航栏的效果，最终实现的效果如下图：

具体实现步骤如下：

根据我前面的文章所讲的RecyclerView的基本使用，我们先来完成基本的recyclerView：

第一步：布局里写一个RecyclerView

第二步：实例化

recyclerView = (RecyclerView) findViewById(R.id.recyclerView);

第三步：获取所需的数据 (这里我们来个真实点的情景，去联网请求数据)

 /**
     * 联网请求所需的url
     */
    public String url="http://api.meituan.com/mmdb/movie/v2/list/rt/order/coming.json?ci=1&limit=12&token=&__vhost=api.maoyan.com&utm_campaign=AmovieBmovieCD-1&movieBundleVersion=6801&utm_source=xiaomi&utm_medium=android&utm_term=6.8.0&utm_content=868030022327462&net=255&dModel=MI%205&uuid=0894DE03C76F6045D55977B6D4E32B7F3C6AAB02F9CEA042987B380EC5687C43&lat=40.100673&lng=116.378619&__skck=6a375bce8c66a0dc293860dfa83833ef&__skts=1463704714271&__skua=7e01cf8dd30a179800a7a93979b430b2&__skno=1a0b4a9b-44ec-42fc-b110-ead68bcc2824&__skcy=sXcDKbGi20CGXQPPZvhCU3%2FkzdE%3D";

 //联网获取数据
        getDataFromNet();

/**
     * 使用okhttpUtils进行联网请求数据
     */
    private void getDataFromNet() {
        OkHttpUtils.
                get()
                .url(url)
                .build()
                .execute(new StringCallback() {
                    @Override
                    public void onError(okhttp3.Call call, Exception e, int id) {
                        Log.e("TAG", "联网失败" + e.getMessage());
                    }

                    @Override
                    public void onResponse(String response, int id) {
                        Log.e("TAG", "联网成功==" + response);

                        //联网成功后使用fastjson解析
                        processData(response);
                    }
                });
    }

/**
     * 使用fastjson进行解析
     *
     * @param json
     */
    private void processData(String json) {
        //这里使用GsonFormat生成对应的bean类
       JSONObject jsonObject = parseObject(json);

        String data = jsonObject.getString("data");
        JSONObject dataObj = JSON.parseObject(data);

        String coming = dataObj.getString("coming");
        List comingslist = parseArray(coming, WaitMVBean.DataBean.ComingBean.class);

        //测试是否解析数据成功
//        String strTest = comingslist.get(0).getCat();
//        Log.e("TAG", strTest + "222");

         //解析数据成功,设置适配器-->
       
        }

    }

第四步：解析数据成功后，创建并设置适配器,并传递相关数据

 //解析数据成功,设置适配器
            MyRecyclerAdapter adapter = new MyRecyclerAdapter( mContext,comingslist);
            recyclerView.setAdapter(adapter);

适配器：

public class MyRecyclerAdapter extends RecyclerView.Adapter {

    private final List comingslist;
    private final Context mContext;
    private final LayoutInflater mLayoutInflater;


    public MyRecyclerAdapter(Context mContext, List comingslist) {
        this.mContext = mContext;
        this.comingslist = comingslist;
        mLayoutInflater = LayoutInflater.from(mContext);
    }

    @Override
    public RecyclerView.ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
        return new MyViewHolder(mLayoutInflater.inflate(R.layout.date_item, null));
    }

    @Override
    public void onBindViewHolder(RecyclerView.ViewHolder holder, int position) {
        MyViewHolder myholder = (MyViewHolder) holder;
        myholder.setData(position);
    }

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

    class MyViewHolder extends RecyclerView.ViewHolder {
        private TextView mv_name;
        private TextView mv_dec;
        private TextView mv_date;
        private ImageView imageView;

        public MyViewHolder(View itemView) {
            super(itemView);
            mv_name = (TextView) itemView.findViewById(R.id.mv_name);
            mv_dec = (TextView) itemView.findViewById(R.id.mv_dec);
            mv_date = (TextView) itemView.findViewById(R.id.mv_date);
            imageView = (ImageView) itemView.findViewById(R.id.image);
        }

        public void setData(int position) {
            WaitMVBean.DataBean.ComingBean coming = comingslist.get(position);

            String name = coming.getNm();
            mv_name.setText(name);

            String date = coming.getShowInfo();
            mv_date.setText(date);

            String dec = coming.getScm();
            mv_dec.setText(dec);

            //注：当你发下图片无法打开是，做个字符串替换即可
            String imagUrl = coming.getImg();
            String newImagUrl = imagUrl.replaceAll("w.h", "50.80");

            //使用Glide加载图片
            Glide.with(mContext)
                    .load(newImagUrl)
                    .into(imageView);
        }
    }
}

item的布局：

第五步：一定不能忘！！！

recycleView不仅要设置适配器还要设置布局管理者,否则图片不显示

GridLayoutManager manager = new GridLayoutManager(this, 1);
            recyclerView.setLayoutManager(manager);

此时 RecyclerView简单的完成效果如下：

下面开始做可推动的悬浮导航栏：

第一步：首先我们来写一个类，它起标记的作用，来放每一个item的对应的悬浮栏的字符串

public class NameBean {
    String name;

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }
}

第二步：自定义一个SectionDecoration 类继承 RecyclerView的ItemDecoration

public class SectionDecoration extends RecyclerView.ItemDecoration {
    private static final String TAG = "SectionDecoration";

    private List dataList;

    private DecorationCallback callback;
    private TextPaint textPaint;
    private Paint paint;
    private int topGap;
    private int alignBottom;
    private Paint.FontMetrics fontMetrics;


    public SectionDecoration(List dataList, Context context, DecorationCallback decorationCallback) {
        Resources res = context.getResources();
        this.dataList = dataList;
        this.callback = decorationCallback;
        //设置悬浮栏的画笔---paint
        paint = new Paint();
        paint.setColor(res.getColor(R.color.colorGray));

        //设置悬浮栏中文本的画笔
        textPaint = new TextPaint();
        textPaint.setAntiAlias(true);
        textPaint.setTextSize(DensityUtil.dip2px(context, 14));
        textPaint.setColor(Color.DKGRAY);
        textPaint.setTextAlign(Paint.Align.LEFT);
        fontMetrics = new Paint.FontMetrics();
        //决定悬浮栏的高度等
        topGap = res.getDimensionPixelSize(R.dimen.sectioned_top);
        //决定文本的显示位置等
        alignBottom = res.getDimensionPixelSize(R.dimen.sectioned_alignBottom);
    }

    @Override
    public void getItemOffsets(Rect outRect, View view, RecyclerView parent, RecyclerView.State state) {
        super.getItemOffsets(outRect, view, parent, state);
        int pos = parent.getChildAdapterPosition(view);
        Log.i(TAG, "getItemOffsets：" + pos);
        String groupId = callback.getGroupId(pos);
        if (groupId.equals("-1")) return;
        //只有是同一组的第一个才显示悬浮栏
        if (pos == 0 || isFirstInGroup(pos)) {
            outRect.top = topGap;
            if (dataList.get(pos).getName() == "") {
                outRect.top = 0;
            }
        } else {
            outRect.top = 0;
        }
    }

    @Override
    public void onDraw(Canvas c, RecyclerView parent, RecyclerView.State state) {
        super.onDraw(c, parent, state);
        int left = parent.getPaddingLeft();
        int right = parent.getWidth() - parent.getPaddingRight();
        int childCount = parent.getChildCount();
        for (int i = 0; i < childCount; i++) {
            View view = parent.getChildAt(i);
            int position = parent.getChildAdapterPosition(view);
            String groupId = callback.getGroupId(position);
            if (groupId.equals("-1")) return;
            String textLine = callback.getGroupFirstLine(position).toUpperCase();
            if (textLine == "") {
                float top = view.getTop();
                float bottom = view.getTop();
                c.drawRect(left, top, right, bottom, paint);
                return;
            } else {
                if (position == 0 || isFirstInGroup(position)) {
                    float top = view.getTop() - topGap;
                    float bottom = view.getTop();
                    //绘制悬浮栏
                    c.drawRect(left, top - topGap, right, bottom, paint);
                    //绘制文本
                    c.drawText(textLine, left, bottom, textPaint);
                }
            }
        }
    }

    @Override
    public void onDrawOver(Canvas c, RecyclerView parent, RecyclerView.State state) {
        super.onDrawOver(c, parent, state);
        int itemCount = state.getItemCount();
        int childCount = parent.getChildCount();
        int left = parent.getPaddingLeft();
        int right = parent.getWidth() - parent.getPaddingRight();
        float lineHeight = textPaint.getTextSize() + fontMetrics.descent;

        String preGroupId = "";
        String groupId = "-1";
        for (int i = 0; i < childCount; i++) {
            View view = parent.getChildAt(i);
            int position = parent.getChildAdapterPosition(view);

            preGroupId = groupId;
            groupId = callback.getGroupId(position);
            if (groupId.equals("-1") || groupId.equals(preGroupId)) continue;

            String textLine = callback.getGroupFirstLine(position).toUpperCase();
            if (TextUtils.isEmpty(textLine)) continue;

            int viewBottom = view.getBottom();
            float textY = Math.max(topGap, view.getTop());
            //下一个和当前不一样移动当前
            if (position + 1 < itemCount) {
                String nextGroupId = callback.getGroupId(position + 1);
                //组内最后一个view进入了header
                if (nextGroupId != groupId && viewBottom < textY) {
                    textY = viewBottom;
                }
            }
            //textY - topGap决定了悬浮栏绘制的高度和位置
            c.drawRect(left, textY - topGap, right, textY, paint);
            //left+2*alignBottom 决定了文本往左偏移的多少（加-->向左移）
            //textY-alignBottom  决定了文本往右偏移的多少  (减-->向上移)
            c.drawText(textLine, left + 2 * alignBottom, textY - alignBottom, textPaint);
        }
    }


    /**
     * 判断是不是组中的第一个位置
     *
     * @param pos
     * @return
     */
    private boolean isFirstInGroup(int pos) {
        if (pos == 0) {
            return true;
        } else {
            // 因为是根据 字符串内容的相同与否 来判断是不是同意组的，所以此处的标记id 要是String类型
            // 如果你只是做联系人列表，悬浮框里显示的只是一个字母，则标记id直接用 int 类型就行了
            String prevGroupId = callback.getGroupId(pos - 1);
            String groupId = callback.getGroupId(pos);
            //判断前一个字符串 与 当前字符串 是否相同
            if (prevGroupId.equals(groupId)) {
                return false;
            } else {
                return true;
            }
        }
    }

    //定义一个借口方便外界的调用
    interface DecorationCallback {
        String getGroupId(int position);

        String getGroupFirstLine(int position);
    }
}

第三步：在向list集合中先把每一个item的起“标记”作用的字符串都加进去

setPullAction(comingslist);

private void setPullAction(List comingslist) {
        dataList = new ArrayList<>();

        for (int i = 0; i < comingslist.size(); i++) {
            NameBean nameBean = new NameBean();
            String name0 = comingslist.get(i).getComingTitle();
            nameBean.setName(name0);
            dataList.add(nameBean);
        }
    }

第四步：在setAdapter（）前，为RecyclerView添加ItemDecoration:

recyclerView.addItemDecoration(new SectionDecoration(dataList,mContext, new SectionDecoration.DecorationCallback() {
               //返回标记id (即每一项对应的标志性的字符串)
                @Override
                public String getGroupId(int position) {
                    if(dataList.get(position).getName()!=null) {
                        return dataList.get(position).getName();
                    }
                    return "-1";
                }

                //获取同组中的第一个内容
                @Override
                public String getGroupFirstLine(int position) {
                    if(dataList.get(position).getName()!=null) {
                        return dataList.get(position).getName();
                    }
                    return "";
                }
            }));

这样就完成了~

再看一眼最终效果感受一下：