Data Binding注意事项

Data Binding的一些问题：

1. 观察数据更新的时候 无论当前activity是否显示在前台都会去更新数据。lifecycles 在onpause之后不会更新UI，重新进入onresume之后才会把之前的值更新到UI中。
2. 如果有嵌套的时候get方法不能重名,见下面代码如果ViewModel和User类同时有绑定getTime()的方法，则只有一个能收到消息，改ViewModel的方法为getTime1()就好了.

<com.example.shibu.myapplication.MyLayout
        android:id="@+id/container"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintTop_toTopOf="parent" >
    <TextView
        android:id="@+id/btn"
        android:text='@{""+vm.user.time}'//time
        android:layout_width="200px"
        android:layout_height="200px" />
        <TextView
            android:id="@+id/btn1"
            android:text='@{""+vm.time1}'//修改为time1和上面的time作区分
            android:layout_width="200px"
            android:layout_height="200px" />
 </com.example.shibu.myapplication.MyLayout>

public class ViewModel  extends BaseObservable{
    public  User user = new User();
    @Bindable
    public int getTime1() { //修改为getTime1 和User里面的方法做区分
        Log.d("bushi",""+time);
        return time;
    }

    public void setTime1(int time) {
        this.time = time;
        notifyPropertyChanged(BR.time1);
    }

    public int time = 0;

}

public class User extends BaseObservable {
    @Bindable
    public int getTime() {
        return time;
    }

    public void setTime(int name) {
        this.time = name;
        notifyPropertyChanged(BR.time);
    }

    int time;
}

3. 关于ViewStub的databinding。ViewStub和别的view有一些不一样，ViewStub一开始并不可见的，当它被使用之后 ViewStub会从视图层级中消失。所以使用android.databinding.ViewStubProxy 对象来监听[ViewStub.OnInflateListener]
   布局代码段如下
   view_stub.xml

<layout xmlns:android="http://schemas.android.com/apk/res/android">
    <data>
        <variable name="vm" type="com.example.shibu.myapplication.ViewModel"/>
    </data>
<com.example.shibu.myapplication.MyLayout xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/container"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    app:layout_constraintBottom_toBottomOf="parent"
    app:layout_constraintLeft_toLeftOf="parent"
    app:layout_constraintRight_toRightOf="parent"
    app:layout_constraintTop_toTopOf="parent"
    tools:showIn="@layout/activity_main">

    <TextView
        android:id="@+id/btn"
        android:text='@{""+vm.user.time}'
        android:layout_width="200px"
        android:layout_height="200px" />

    <TextView
        android:id="@+id/btn1"
        android:text='@{""+vm.time1}'
        android:layout_width="200px"
        android:layout_height="200px" />
</com.example.shibu.myapplication.MyLayout>
</layout>

activity_main.xml

<ViewStub
    android:id="@+id/viewstub"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout="@layout/view_stub"/>
</android.support.constraint.ConstraintLayout>

绑定代码段如下：

        final ViewModel viewModel = new ViewModel();
        viewModel.user.setTime(time);
        final ActivityMainBinding activityMainBinding = DataBindingUtil.setContentView(this,R.layout.activity_main);
        activityMainBinding.viewstub.setOnInflateListener(new ViewStub.OnInflateListener() {
            @Override
            public void onInflate(ViewStub stub, View inflated) {
                ViewStubBinding viewDataBinding = DataBindingUtil.bind(inflated);
                viewDataBinding.setVm(viewModel);

            }
        });
        activityMainBinding.viewstub.getViewStub().inflate();