FrameLayout的子类ViewAnimator

ViewAnimator

public class ViewAnimator extends FrameLayout 

FrameLayout容器的基类，用于在其视图之间切换时执行动画。

我们都了解FrameLayout布局的特性，在FrameLayout中添加的View都默认位于左上角，按照添加的顺序，最后添加的View位置最上层。

ViewAnimator的使用就是调整ViewAnimator包裹的子View的显示层次，可以通过setDisplayedChild(int whichChild)方法，设置哪一个子View将被显示。

布局

<LinearLayout      xmlns:android="http://schemas.android.com/apk/res/android"      android:orientation="vertical"      android:layout_width="match_parent"      android:layout_height="match_parent"      android:id="@+id/sample_main_layout">    <ViewAnimator          android:id="@+id/sample_output"          android:layout_width="match_parent"          android:layout_height="0px"          android:layout_weight="1">        <ScrollView              style="@style/Widget.SampleMessageTile"              android:layout_width="match_parent"              android:layout_height="match_parent">            <TextView                  style="@style/Widget.SampleMessage"                  android:layout_width="match_parent"                  android:layout_height="wrap_content"                  android:paddingLeft="@dimen/horizontal_page_margin"                  android:paddingRight="@dimen/horizontal_page_margin"                  android:paddingTop="@dimen/vertical_page_margin"                  android:paddingBottom="@dimen/vertical_page_margin"                  android:text="@string/intro_message" />        </ScrollView>        <fragment              android:name="com.example.android.common.logger.LogFragment"              android:id="@+id/log_fragment"              android:layout_width="match_parent"              android:layout_height="match_parent" />    </ViewAnimator>    <View          android:layout_width="match_parent"          android:layout_height="1dp"          android:background="@android:color/darker_gray" />    <FrameLayout          android:id="@+id/sample_content_fragment"          android:layout_weight="2"          android:layout_width="match_parent"          android:layout_height="0px" /></LinearLayout>

menu

<menu xmlns:android="http://schemas.android.com/apk/res/android"      xmlns:tools="http://schemas.android.com/tools"      tools:ignore="AppCompatResource">    <item android:id="@+id/menu_toggle_log"          android:showAsAction="always"          android:title="Show Log" /></menu>

Activity

public class MainActivity extends SampleActivityBase {    // Whether the Log Fragment is currently shown    private boolean mLogShown;    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_main);        if (savedInstanceState == null) {            FragmentTransaction transaction = getSupportFragmentManager().beginTransaction();            SwipeRefreshListFragmentFragment fragment = new SwipeRefreshListFragmentFragment();            transaction.replace(R.id.sample_content_fragment, fragment);            transaction.commit();        }    }    @Override    public boolean onCreateOptionsMenu(Menu menu) {        getMenuInflater().inflate(R.menu.main, menu);        return true;    }    @Override    public boolean onPrepareOptionsMenu(Menu menu) {        MenuItem logToggle = menu.findItem(R.id.menu_toggle_log);        //R.id.sample_output对应的组件是否是ViewAnimator或其子类的一个实例，若是，menu_toggle_log，显示        logToggle.setVisible(findViewById(R.id.sample_output) instanceof ViewAnimator);        //logFragment显示的状态不同显示不同字符        logToggle.setTitle(mLogShown ? Hide Log: Show Log);        return super.onPrepareOptionsMenu(menu);    }    @Override    public boolean onOptionsItemSelected(MenuItem item) {        //用于修改menu_toggle_log显示的字符串及ViewAnimator显示的view        switch(item.getItemId()) {            case R.id.menu_toggle_log:                mLogShown = !mLogShown;                ViewAnimator output = (ViewAnimator) findViewById(R.id.sample_output);                if (mLogShown) {                    //显示LogFragment                    output.setDisplayedChild(1);                } else {                    //显示user guide                    output.setDisplayedChild(0);                }                //使Activity的选项菜单无效。                //这将导致菜单的相关演示文稿通过在下一次请求菜单时                //通过调用onCreateOptionsMenu和onPrepareOptionsMenu进行完全更新。                supportInvalidateOptionsMenu();                return true;        }        return super.onOptionsItemSelected(item);    }}