在Android Wear上实现GridViewPager的正确方法是什么？

Question

我正在尝试实现一个GridViewPager，以便在两个独特的视图之间进行切换。到目前为止，我还没有能够添加任何视图。以下是我的代码。

public class Gridder extends Activity {

private TextView mTextView;
GridViewPager gridViewPager;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_gridder);
    final WatchViewStub stub = (WatchViewStub) findViewById(R.id.watch_view_stub);
    final LayoutInflater inflater = getLayoutInflater();
    stub.setOnLayoutInflatedListener(new WatchViewStub.OnLayoutInflatedListener() {
        @Override
        public void onLayoutInflated(WatchViewStub stub) {
            gridViewPager = (GridViewPager) findViewById(R.id.pager);
            gridViewPager.setAdapter(new MyGridViewPagerAdapter());
            gridViewPager.addView(inflater.inflate(R.layout.selector_generic, stub));;
        }
    });
}

private class MyGridViewPagerAdapter extends GridPagerAdapter {
    @Override
    protected void destroyItem(ViewGroup arg0, int arg1, int arg2, Object arg3) {
    }

    @Override
    public int getColumnCount(int arg0) {
        return 1;
    }

    @Override
    public int getRowCount() {
        return 1;
    }

    @Override
    protected Object instantiateItem(ViewGroup arg0, int arg1, int arg2) {
        return null;
    }

    @Override
    public boolean isViewFromObject(View arg0, Object arg1) {
        return false;
    }
}

在主视图 stub 的矩形子视图中，我有一个id为 pager 的 GridViewPager，就像我之前提到的那样：

<android.support.wearable.view.GridViewPager
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/pager"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:keepScreenOn="true" />

这段代码会抛出一个非法状态异常并且会提示我的子视图已经有了父级对象。具体请看下方：

...

07-16 14:44:40.847  12940-12940/com.larvalabs.weartest E/AndroidRuntime﹕ FATAL EXCEPTION: main
Process: com.larvalabs.weartest, PID: 12940
java.lang.IllegalStateException: The specified child already has a parent. You must call removeView() on the child's parent first.
        at android.view.ViewGroup.addViewInner(ViewGroup.java:3561)
        at android.view.ViewGroup.addView(ViewGroup.java:3414)
        at android.support.wearable.view.GridViewPager.addView(GridViewPager.java:1088)
        at android.view.ViewGroup.addView(ViewGroup.java:3359)
        at android.view.ViewGroup.addView(ViewGroup.java:3335)
        at com.larvalabs.weartest.Gridder$1.onLayoutInflated(Gridder.java:30)
        at android.support.wearable.view.WatchViewStub.inflate(WatchViewStub.java:133)
        at android.support.wearable.view.WatchViewStub.onMeasure(WatchViewStub.java:141)
        at android.view.View.measure(View.java:16648)
        at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5125)
        at android.widget.FrameLayout.onMeasure(FrameLayout.java:310)
        at android.view.View.measure(View.java:16648)
        at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5125)
        at android.widget.FrameLayout.onMeasure(FrameLayout.java:310)
        at com.android.internal.policy.impl.PhoneWindow$DecorView.onMeasure(PhoneWindow.java:2321)
        at android.view.View.measure(View.java:16648)
        at android.view.ViewRootImpl.performMeasure(ViewRootImpl.java:1959)
        at android.view.ViewRootImpl.measureHierarchy(ViewRootImpl.java:1145)
        at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1340)
        at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1032)
        at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:5657)
        at android.view.Choreographer$CallbackRecord.run(Choreographer.java:761)
        at android.view.Choreographer.doCallbacks(Choreographer.java:574)
        at android.view.Choreographer.doFrame(Choreographer.java:544)
        at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:747)
        at android.os.Handler.handleCallback(Handler.java:733)
        at android.os.Handler.dispatchMessage(Handler.java:95)
        at android.os.Looper.loop(Looper.java:136)
        at android.app.ActivityThread.main(ActivityThread.java:5026)
        at java.lang.reflect.Method.invokeNative(Native Method)
        at java.lang.reflect.Method.invoke(Method.java:515)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:777)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:602)
        at dalvik.system.NativeStart.main(Native Method)

- nickjm

Answer 1

堆栈跟踪解释：

首先，以下一行是错误的：

gridViewPager.addView(inflater.inflate(R.layout.selector_generic, stub));

inflate(int resource, ViewGroup root)方法，如果root!=null，则与inflate(int resource, ViewGroup root, boolean attachToRoot)方法相同，最后一个参数为true。根据文档，将从resource中填充视图并将其附加到根视图——然后返回一个根视图。

这将尝试将新填充的视图附加到stub，然后尝试将stub（使用指定root调用inflate()的结果）附加到gridViewPager。但是，stub已经有父项（它已经附加到您的活动的视图层次结构中）。这是堆栈跟踪的解释：)
请注意，您不应通过.addView()方法向gridViewPager添加视图-您应该通过适配器完成，并且应该删除该行。

GridPagerAdapter示例：

这里是GridPagerAdapter的简单实现；

private class MyGridViewPagerAdapter extends GridPagerAdapter {
    @Override
    public int getColumnCount(int arg0) {
        return 2;
    }

    @Override
    public int getRowCount() {
        return 2;
    }

    @Override
    protected Object instantiateItem(ViewGroup container, int row, int col) {
        final View view = LayoutInflater.from(getApplicationContext()).inflate(R.layout.grid_view_pager_item, container, false);
        final TextView textView = (TextView) view.findViewById(R.id.textView);
        textView.setText(String.format("Page:\n%1$s, %2$s", row, col));
        container.addView(view);
        return view;
    }

    @Override
    protected void destroyItem(ViewGroup container, int row, int col, Object view) {
        container.removeView((View)view);
    }

    @Override
    public boolean isViewFromObject(View view, Object object) {
        return view==object;
    }
}

grid_view_pager_item.xml的内容：

<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:padding="10dp">

    <TextView
        android:id="@+id/textView"
        android:layout_width="match_parent"
        android:layout_height="100dp"
        android:layout_gravity="center_vertical"
        android:gravity="center"
        android:background="#4400ff00"
        android:textColor="#000000"
        android:textSize="26sp"/> 

</FrameLayout>

这是2x2网格最终结果。其中两个屏幕处于静止状态，另外两个屏幕在页面半滚动时被拍照：

---

还想了解更多吗？

这只是使用标准GridPagerAdapter的示例。如果您想要更高级的内容，可以使用FragmentGridPagerAdapter、CardFragments和页面背景，请查看位于平台示例中的GridViewPager示例：
{sdk_root}/samples/android-20/wearable/GridViewPager

- Maciej Ciemięga

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在GridViewPager中添加页面指示器是否可行？ - KunalK

有一个 setOnPageChanngedListener 可以用来实现这个功能。 - Mark Renouf

Maciej Ciemięga，谢谢你，这是一个非常好的例子，但我加了背景后遇到了一个问题。 @Override public ImageReference getBackground(int row, int column) { // default, if nothing else return ImageReference.forDrawable(R.drawable.debug_background_1); }当我上下滑动时，会出现令人讨厌的白屏闪烁，有什么方法可以解决吗？ - Donal Rafferty

现在该库中包含了一个DotsPageIndicator。http://developer.android.com/reference/android/support/wearable/view/DotsPageIndicator.html - Mark Renouf