android - 检查 Framelayout 上是否存在 fragment

Question

我在我的项目中使用 ViewPager 和 3 个 fragment 。这 3 个 fragment 之一必须在其中包含另一个 fragment ，因为我在 fragment 的布局中定义了一个 FrameLayout:

<RelativeLayout 
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent" >

    <LinearLayout
        android:id="@+id/valuesContainer"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:layout_marginTop="20dp" >

        ...        
    </LinearLayout>

    <FrameLayout
        android:id="@+id/model3d_container"
        android:layout_width="fill_parent"
        android:layout_height="fill_parent"
        android:layout_below="@+id/valuesContainer"
        android:layout_centerHorizontal="true"
        android:layout_margin="15dp"
        android:layout_marginTop="20dp" />
</RelativeLayout>

现在我以编程方式添加新 fragment :

@Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        View view = inflater.inflate(R.layout.layout_row3d, container, false);

        /*Check if fragment is already loaded*/
        Fragment frag = getActivity().getSupportFragmentManager().findFragmentById(R.id.model3d_container);
        if (frag == null) {
            /*load fragment with 3d model*/
            Fragment modelFragment = new Obj3DView();
            FragmentTransaction transaction = getChildFragmentManager().beginTransaction();
            transaction.add(R.id.model3d_container, modelFragment).commit();
        }
        return view;
    }

但是当我在 ViewPager 的 View 中导航时，当我返回到包含子 fragment 的 fragment 时，应用程序崩溃了。看Log，好像跟子 fragment 加载有关系。我已经定义了一个方法来检查 fragment 是否已加载，如果是，则不加载，但我认为无论如何都会重新加载。

10-13 12:48:34.809: E/AndroidRuntime(26460): FATAL EXCEPTION: main
10-13 12:48:34.809: E/AndroidRuntime(26460): Process: com.rowingsoft, PID: 26460
10-13 12:48:34.809: E/AndroidRuntime(26460): java.lang.IllegalStateException: The specified child already has a parent. You must call removeView() on the child's parent first.
10-13 12:48:34.809: E/AndroidRuntime(26460):    at android.view.ViewGroup.addViewInner(ViewGroup.java:3759)
10-13 12:48:34.809: E/AndroidRuntime(26460):    at android.view.ViewGroup.addView(ViewGroup.java:3612)
10-13 12:48:34.809: E/AndroidRuntime(26460):    at android.view.ViewGroup.addView(ViewGroup.java:3557)
10-13 12:48:34.809: E/AndroidRuntime(26460):    at android.view.ViewGroup.addView(ViewGroup.java:3533)
10-13 12:48:34.809: E/AndroidRuntime(26460):    at android.support.v4.app.NoSaveStateFrameLayout.wrap(NoSaveStateFrameLayout.java:40)
10-13 12:48:34.809: E/AndroidRuntime(26460):    at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:931)
10-13 12:48:34.809: E/AndroidRuntime(26460):    at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1104)
10-13 12:48:34.809: E/AndroidRuntime(26460):    at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1086)
10-13 12:48:34.809: E/AndroidRuntime(26460):    at android.support.v4.app.FragmentManagerImpl.dispatchActivityCreated(FragmentManager.java:1884)
10-13 12:48:34.809: E/AndroidRuntime(26460):    at android.support.v4.app.Fragment.performActivityCreated(Fragment.java:1514)
10-13 12:48:34.809: E/AndroidRuntime(26460):    at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:947)
10-13 12:48:34.809: E/AndroidRuntime(26460):    at android.support.v4.app.FragmentManagerImpl.attachFragment(FragmentManager.java:1280)
10-13 12:48:34.809: E/AndroidRuntime(26460):    at android.support.v4.app.BackStackRecord.run(BackStackRecord.java:672)
10-13 12:48:34.809: E/AndroidRuntime(26460):    at android.support.v4.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1467)
10-13 12:48:34.809: E/AndroidRuntime(26460):    at android.support.v4.app.FragmentManagerImpl.executePendingTransactions(FragmentManager.java:472)
10-13 12:48:34.809: E/AndroidRuntime(26460):    at android.support.v4.app.FragmentPagerAdapter.finishUpdate(FragmentPagerAdapter.java:141)
10-13 12:48:34.809: E/AndroidRuntime(26460):    at android.support.v4.view.ViewPager.populate(ViewPager.java:1068)
10-13 12:48:34.809: E/AndroidRuntime(26460):    at android.support.v4.view.ViewPager.populate(ViewPager.java:914)
10-13 12:48:34.809: E/AndroidRuntime(26460):    at android.support.v4.view.ViewPager$3.run(ViewPager.java:244)
10-13 12:48:34.809: E/AndroidRuntime(26460):    at android.view.Choreographer$CallbackRecord.run(Choreographer.java:803)
10-13 12:48:34.809: E/AndroidRuntime(26460):    at android.view.Choreographer.doCallbacks(Choreographer.java:603)
10-13 12:48:34.809: E/AndroidRuntime(26460):    at android.view.Choreographer.doFrame(Choreographer.java:572)
10-13 12:48:34.809: E/AndroidRuntime(26460):    at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:789)
10-13 12:48:34.809: E/AndroidRuntime(26460):    at android.os.Handler.handleCallback(Handler.java:733)
10-13 12:48:34.809: E/AndroidRuntime(26460):    at android.os.Handler.dispatchMessage(Handler.java:95)
10-13 12:48:34.809: E/AndroidRuntime(26460):    at android.os.Looper.loop(Looper.java:157)
10-13 12:48:34.809: E/AndroidRuntime(26460):    at android.app.ActivityThread.main(ActivityThread.java:5356)
10-13 12:48:34.809: E/AndroidRuntime(26460):    at java.lang.reflect.Method.invokeNative(Native Method)
10-13 12:48:34.809: E/AndroidRuntime(26460):    at java.lang.reflect.Method.invoke(Method.java:515)
10-13 12:48:34.809: E/AndroidRuntime(26460):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1265)
10-13 12:48:34.809: E/AndroidRuntime(26460):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1081)
10-13 12:48:34.809: E/AndroidRuntime(26460):    at dalvik.system.NativeStart.main(Native Method)

Answer 1

代替 transaction.add 使用 transaction.replace