DataBinding入门

小知识，大挑战！本文正在参与“程序员必备小知识”创作活动。

字面意思数据绑定
优点：灵活解耦，避免编写重复性的模板代码
缺点：方法调用在xml中进行，不进行编译检查，运行时才检查，比如需要传int，我传string照样不报错
（一）直接在布局文件中操作类中的数据！

   <TextView
            android:id="@+id/textView2"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_marginTop="85dp"
            android:layout_marginEnd="4dp"
            android:layout_marginRight="4dp"
            android:text="@{StarUtils.getStar(ido.star)}"
            app:layout_constraintEnd_toEndOf="@+id/textView"
            app:layout_constraintTop_toBottomOf="@+id/textView" />

1在module的build.gradle中配置；需要rebuild构建一下

dataBinding{
            enabled=true
        }

android {
    compileSdkVersion 29

    defaultConfig {
        applicationId "com.dongnaoedu.jetpackstudy"
        minSdkVersion 27
        targetSdkVersion 29
        versionCode 1
        versionName "1.0"

        testInstrumentationRunner "androidx.test.runner.AndroidJUnitRunner"
        dataBinding{
            enabled=true
        }
    }

2布局文件 中alt+回车，切换成databinding布局

<?xml version="1.0" encoding="utf-8"?>
<layout 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">

    <data>

    </data>

    <androidx.constraintlayout.widget.ConstraintLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        tools:context=".DataBindingActivity">

    </androidx.constraintlayout.widget.ConstraintLayout>
</layout>

3通过variable标签绑定类与布局文件

package com.dongnaoedu.jetpackstudy;

public class Ido {
    public String name;
    public String star;

    public Ido(final String mName, final String mStar) {
        name = mName;
        star = mStar;
    }
}

此布局文件通过@{}直接调用类中的属性赋值

<?xml version="1.0" encoding="utf-8"?>
<layout 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">

    <data>
        <variable
            name="ido"
            type="com.example.databinding.Ido" />

    </data>

    <androidx.constraintlayout.widget.ConstraintLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        tools:context="com.example.databinding.DataBindingActivity">

        <TextView
            android:id="@+id/textView"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_marginTop="139dp"
            android:layout_marginEnd="163dp"
            android:layout_marginRight="163dp"
            android:text="@{ido.name}"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintTop_toTopOf="parent" />

        <TextView
            android:id="@+id/textView2"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_marginTop="85dp"
            android:layout_marginEnd="4dp"
            android:layout_marginRight="4dp"
            android:text="@{ido.star}"
            app:layout_constraintEnd_toEndOf="@+id/textView"
            app:layout_constraintTop_toBottomOf="@+id/textView" />
    </androidx.constraintlayout.widget.ConstraintLayout>
</layout>

DataBinding在Activity中的使用

public class DataBindingActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        //注意：ActivityDataBinding与activity_data_binding一一对应
      ActivityDataBindingBinding activityMainBinding = DataBindingUtil.setContentView(this,    R.layout.activity_data_binding);
        Ido ido = new Ido("wy", "五星");
        activityMainBinding.setIdo(ido);
    }
}

（二）点击监听事件的实现
1创建事件监听回调机制

public class EventHandleListener {
    private Context context;

    public EventHandleListener(Context context) {
        this.context = context;
    }

    public void buttonOnClick(View view){
        Log.e("wy", "buttonOnClick: " );
        Toast.makeText(context,"喜欢",Toast.LENGTH_SHORT).show();
    }
}

2xml布局中做关联

<variable
            name="eventHandle"
            type="com.example.databinding.EventHandleListener" />

设置具体控件点击事件

  <Button
            android:id="@+id/button"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_marginEnd="122dp"
            android:layout_marginRight="122dp"
            android:layout_marginBottom="329dp"
            android:onClick="@{eventHandle.buttonOnClick}"
            android:text="like"
            app:layout_constraintBottom_toBottomOf="parent"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintTop_toBottomOf="@+id/textView" />

xml全代码

<?xml version="1.0" encoding="utf-8"?>
<layout 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">



    <androidx.constraintlayout.widget.ConstraintLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        tools:context="com.example.databinding.DataBindingActivity">

        <TextView
            android:id="@+id/textView"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_marginTop="139dp"
            android:layout_marginEnd="163dp"
            android:layout_marginRight="163dp"
            android:layout_marginBottom="198dp"
            android:text="@{ido.name}"
            tools:text="李狗娃"
            app:layout_constraintBottom_toTopOf="@+id/button"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintTop_toTopOf="parent" />

        <TextView
            android:id="@+id/textView2"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_marginTop="85dp"
            android:layout_marginEnd="4dp"
            android:layout_marginRight="4dp"
            tools:text="五星"
            android:text="@{StarUtils.getStar(ido.star)}"
            app:layout_constraintEnd_toEndOf="@+id/textView"
            app:layout_constraintTop_toBottomOf="@+id/textView" />

        <Button
            android:id="@+id/button"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_marginEnd="122dp"
            android:layout_marginRight="122dp"
            android:layout_marginBottom="329dp"
            android:onClick="@{eventHandle.buttonOnClick}"
            android:text="like"
            app:layout_constraintBottom_toBottomOf="parent"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintTop_toBottomOf="@+id/textView" />
    </androidx.constraintlayout.widget.ConstraintLayout>
    <data>
        <variable
            name="ido"
            type="com.example.databinding.Ido" />
        <variable
            name="eventHandle"
            type="com.example.databinding.EventHandleListener" />
        <import type="com.example.databinding.StarUtils"/>

    </data>
</layout>

3最重要的一步设置监听事件（传上下文）

activityMainBinding.setEventHandle(new EventHandleListener(this));

public class DataBindingActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
//        setContentView(R.layout.activity_data_binding);
        ActivityDataBindingBinding activityMainBinding = DataBindingUtil.setContentView(this, R.layout.activity_data_binding);
        Ido ido = new Ido("wy", 5);
        activityMainBinding.setIdo(ido);
        activityMainBinding.setEventHandle(new EventHandleListener(this));
    }
}