有时在用片段填充 viewpager 时“活动已被破坏”

Question

我的 viewpager v22 + FragmentPagerAdapter 收到来自所有版本的 android 4+ 和 5+ 的崩溃报告。 viewpager 在一个片段中，并且 pager 适配器正在使用 childFragmentManager 它很少发生，大约有 1/200 用户。

java.lang.IllegalStateException: Activity has been destroyed
at android.support.v4.app.FragmentManagerImpl.void enqueueAction(java.lang.Runnable,boolean)(SourceFile:1397)
at android.support.v4.app.BackStackRecord.int commitInternal(boolean)(SourceFile:636)
at android.support.v4.app.BackStackRecord.int commitAllowingStateLoss()(SourceFile:619)
at android.support.v4.app.FragmentPagerAdapter.void finishUpdate(android.view.ViewGroup)(SourceFile:139)
at android.support.v4.view.ViewPager.void populate(int)(SourceFile:1073)
at android.support.v4.view.ViewPager.void populate()(SourceFile:919)
at android.support.v4.view.ViewPager.void onMeasure(int,int)(SourceFile:1441)
at android.view.View.measure(View.java:16574)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5140)
at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1406)
at android.widget.LinearLayout.measureVertical(LinearLayout.java:697)
at android.widget.LinearLayout.onMeasure(LinearLayout.java:590)
at android.view.View.measure(View.java:16574)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5140)
at android.widget.FrameLayout.onMeasure(FrameLayout.java:310)
at android.view.View.measure(View.java:16574)
at android.widget.LinearLayout.measureVertical(LinearLayout.java:849)
at android.widget.LinearLayout.onMeasure(LinearLayout.java:590)
at android.view.View.measure(View.java:16574)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5140)
at android.widget.FrameLayout.onMeasure(FrameLayout.java:310)
at android.view.View.measure(View.java:16574)
at android.widget.RelativeLayout.measureChildHorizontal(RelativeLayout.java:719)
at android.widget.RelativeLayout.onMeasure(RelativeLayout.java:455)
at android.view.View.measure(View.java:16574)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5140)
at android.widget.FrameLayout.onMeasure(FrameLayout.java:310)
at android.view.View.measure(View.java:16574)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5140)
at android.support.v7.internal.widget.ActionBarOverlayLayout.void onMeasure(int,int)(SourceFile:453)
at android.view.View.measure(View.java:16574)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5140)
at android.widget.FrameLayout.onMeasure(FrameLayout.java:310)
at android.view.View.measure(View.java:16574)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5140)
at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1406)
at android.widget.LinearLayout.measureVertical(LinearLayout.java:697)
at android.widget.LinearLayout.onMeasure(LinearLayout.java:590)
at android.view.View.measure(View.java:16574)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5140)
at android.widget.FrameLayout.onMeasure(FrameLayout.java:310)
at com.android.internal.policy.impl.PhoneWindow$DecorView.onMeasure(PhoneWindow.java:2423)
at android.view.View.measure(View.java:16574)
at android.view.ViewRootImpl.performMeasure(ViewRootImpl.java:1955)
at android.view.ViewRootImpl.measureHierarchy(ViewRootImpl.java:1151)
at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1333)
at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1038)
at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:5890)
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:5118)
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:790)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:606)
at dalvik.system.NativeStart.main(Native Method)

从 bugsense 面包屑中，它在返回活动时发生，尽管我无法在任何内存条件下的任何设备上重现它，或者在开发人员选项中打开“不保留活动”。整个应用程序仅是纵向的，但从其他应用程序以横向方式返回它不会导致任何问题。

我正在使用 onDetach 技巧，其中我得到“mChildFragmentManager”并将其清空，以及可能使事情复杂化的 fragmentPagerAdapter 技巧，尽管我不相信它们会导致这个问题。

有谁知道如何始终如一地重现此崩溃或如何解决它？我不知道当活动被销毁时，viewpager 或片段管理器如何仍然处于活动状态。 编辑：更多代码以防万一。

  public class HomePageAdapter extends FragmentPagerAdapter implements CustomPagerSlidingTabStrip.BadgeTabProvider {

    public HomePageAdapter(FragmentManager fm)
    {
        super(fm);
    }

     @Override
      public Parcelable saveState(){
          return new Bundle();
      }
      @Override
      public void restoreState(Parcelable arg0, ClassLoader arg1) {
          //do nothing here! no call to super.restoreState(arg0, arg1);
      }
    @Override
    public Fragment getItem(int i) {
        Fragment hf;
        switch (i){

            case 0:
                hf= MyFragment.newInstance(MyFragment.MODE_FRIENDS);
                break;
            case 1:
                hf= OtherFragment.newInstance(parameter);
                break;
            default:
                return null;

        }
        hf.setRetainInstance(false);
        return hf;
    }

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

    @Override
    public String getPageTitle(int position) {
        switch (position){
            case 0:
                return "Tab 1";
            case 1:
                return "Tab 2";
            default:
                return "";

        }

    }

}

在我拥有的每一个片段中

    @Override
public void onDetach(){
    super.onDetach();
    try {
        Field childFragmentManager = Fragment.class.getDeclaredField("mChildFragmentManager");
        childFragmentManager.setAccessible(true);
        childFragmentManager.set(this, null);

    } catch (NoSuchFieldException e) {
        Log.e("Hang frag " ,"no such field mchildfragmentmanager err " + e.toString());
        //throw new RuntimeException(e);
    } catch (IllegalAccessException e) {
        Log.e("Hang frag " ," illegal access mchildfragmentmanager err " + e.toString());
      //  throw new RuntimeException(e);
    }
}

编辑： 此问题不再发生在最新版本的支持库 v4 22.2 上。我还从适配器中删除了 saveState 和 restoreState 方法，但我怀疑这是问题所在。这可能是一个我们永远不会知道答案的神秘片段生命周期问题。

Answer 1

因为没有任何代码，我无法准确告诉你问题出在哪里，但我可以告诉你这个问题是如何发生的：

正如您在fragment manager 的源代码中所见，它会在任何事务之前检查活动状态：

public void  enqueueAction(Runnable action, boolean allowStateLoss) {
        if (!allowStateLoss) {
            checkStateLoss();
        }
        synchronized (this) {
            if (mDestroyed || mActivity == null) {
                throw new IllegalStateException("Activity has been destroyed");
            }
            if (mPendingActions == null) {
                mPendingActions = new ArrayList<Runnable>();
            }
            mPendingActions.add(action);
            if (mPendingActions.size() == 1) {
                mActivity.mHandler.removeCallbacks(mExecCommit);
                mActivity.mHandler.post(mExecCommit);
            }
        }
    }

因此，如果您的活动已被破坏或为空，并且FragmentPagerAdapter 尝试提交片段（== 更新自身）（如您在 logcat 中看到的： android.support.v4.app.FragmentPagerAdapter.void finishUpdate(android.view.ViewGroup)(SourceFile:139)），您可能会收到此错误。

Answer 2

如果这个问题发生在一个人身上，它一定会发生在任何其他设备上。

当您尝试获取视图寻呼机的附加活动的引用并且该活动已进入休息状态时，可能会由于使用getActivity() 而出现此问题。

如果可能，请不要使用活动的引用：

getActivity().somemethod.something

相反，在onAttach() 的片段中创建您的活动的类引用，并使用该引用来处理视图寻呼机。

希望这能解决您的问题...干杯！！！