Android 嵌套 fragment 问题 "java.lang.IllegalStateException: Activity has been destroyed"

Question

正如您可能知道的那样，Android 也支持嵌套 fragment ，也通过 API 级别 17 的支持库。所以基本上我正在尝试将嵌套 fragment 添加到 ViewPager 的 fragment 之一中，并熟悉这个新的好功能。

在第一次启动应用程序时，一切都按预期工作，即我可以添加子 fragment 、浏览这些 fragment 、处理返回堆栈等。

但问题是，当我通过单击“后退”按钮离开应用程序并重新启动应用程序时，大多数时候我都会遇到以下异常，但并非总是如此:

java.lang.IllegalStateException: Activity has been destroyed
    at android.support.v4.app.FragmentManagerImpl.enqueueAction(FragmentManager.java:1342)
    at android.support.v4.app.BackStackRecord.commitInternal(BackStackRecord.java:595)
    at android.support.v4.app.BackStackRecord.commit(BackStackRecord.java:574)
    at com.cnlms.andnestedfragments.ui.fragments.FragWrapper.addChildFragment(FragWrapper.java:145)
    at com.cnlms.andnestedfragments.ui.fragments.FragWrapper.onActivityCreated(FragWrapper.java:96)
    at android.support.v4.app.Fragment.performActivityCreated(Fragment.java:1468)
    at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:931)
    at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1088)
    at android.support.v4.app.BackStackRecord.run(BackStackRecord.java:682)
    at android.support.v4.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1444)
    at android.support.v4.app.FragmentManagerImpl.executePendingTransactions(FragmentManager.java:461)
    at android.support.v4.app.FragmentStatePagerAdapter.finishUpdate(FragmentStatePagerAdapter.java:163)
    at android.support.v4.view.ViewPager.populate(ViewPager.java:1012)
    at android.support.v4.view.ViewPager.populate(ViewPager.java:881)
    at android.support.v4.view.ViewPager.onMeasure(ViewPager.java:1366)
    at android.view.View.measure(View.java:15172)
    at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:4814)
    at android.widget.FrameLayout.onMeasure(FrameLayout.java:310)
    at android.view.View.measure(View.java:15172)
    at android.widget.LinearLayout.measureVertical(LinearLayout.java:833)
    at android.widget.LinearLayout.onMeasure(LinearLayout.java:574)
    at android.view.View.measure(View.java:15172)
    at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:4814)
    at android.widget.FrameLayout.onMeasure(FrameLayout.java:310)
    at com.android.internal.policy.impl.PhoneWindow$DecorView.onMeasure(PhoneWindow.java:2148)
    at android.view.View.measure(View.java:15172)
    at android.view.ViewRootImpl.performMeasure(ViewRootImpl.java:1848)
    at android.view.ViewRootImpl.measureHierarchy(ViewRootImpl.java:1100)
    at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1273)
    at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:998)
    at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:4212)
    at android.view.Choreographer$CallbackRecord.run(Choreographer.java:725)
    at android.view.Choreographer.doCallbacks(Choreographer.java:555)
    at android.view.Choreographer.doFrame(Choreographer.java:525)
    at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:711)
    at android.os.Handler.handleCallback(Handler.java:615)
    at android.os.Handler.dispatchMessage(Handler.java:92)
    at android.os.Looper.loop(Looper.java:137)
    at android.app.ActivityThread.main(ActivityThread.java:4745)
    at java.lang.reflect.Method.invokeNative(Native Method)
    at java.lang.reflect.Method.invoke(Method.java:511)
    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:786)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
    at dalvik.system.NativeStart.main(Native Method)

整个项目可用here .

Activity 是否可以在某个时候为空？我的意思是当我调用 getChildFragmentManager() 时， Activity 不应该附加到 fragment 管理器吗？任何建议将不胜感激。

有关该应用程序的更多详细信息，

ViewPager 托管两个 fragment 实例:FragRegular 和 FragWrapper。第一个只是一个简单的无用 fragment ；第二个，FragWrapper，充当父 fragment ，即子 fragment 的容器。 FragWrapper 的布局如下所示:

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical">

    <!--
        Adds nested child fragments when clicked
    -->
    <Button
        android:id="@+id/btn_go_deep"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_alignParentBottom="true"
        android:text="Go Nesty!"/>

    <!--
        Nested Fragment Container
    -->
    <FrameLayout
        android:id="@+id/frag_container"
        android:orientation="vertical"
        android:layout_width="fill_parent"
        android:layout_height="match_parent"
        android:layout_above="@id/btn_go_deep"/>

</RelativeLayout>

所以基本上第一个子 fragment 是在 FragWrapper 的 onActivityCreated() 回调方法中添加到 FragWrapper 中的，随后的子 fragment 是在运行时添加的，通过单击按钮触发。 FragWrapper 类如下所示:

public final class FragWrapper extends BaseFragment {
    /**
     *
     *  The Wrapper Fragment that hosts nested child fragments.
     *
     *  First child fragment is added in onActivityCreated() callback
     *
     *  More child fragments can be added at runtime by clicking 'Go Nesty!'
     *  button.
     *
    */

    /**
     *  Holds back stacked fragment tags
     */
    private Stack<String> backStack;

    /**
     *  Child Fragment Manager
     */
    private FragmentManager fm;

    /**
     *  Fragment Tags
     */
    private int fragCount = 1;


    private static FragWrapper instance;

    public static FragWrapper getInstance() {

        if (instance == null) {

            instance = new FragWrapper();

        }

        return instance;

    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {

        View view = inflater.inflate(R.layout.frag_wrapper, container, false);

        view.findViewById(R.id.btn_go_deep).setOnClickListener(new View.OnClickListener() {

            @Override
            public void onClick(View v) {

                /**
                 *  Adds nested child fragments
                 */
                fragCount+=1;

                addChildFragment(
                        FragChild.newInstance(fragCount),
                        String.valueOf(fragCount),
                        true
                );
            }

        });

        return view;
    }

    @Override
    public void onActivityCreated(Bundle savedInstanceState) {

        super.onActivityCreated(savedInstanceState);

        /**
         *  Add Initial Fragment
         */
        addChildFragment(
                FragChild.newInstance(fragCount),
                String.valueOf(fragCount),
                false
        );

    }

    private void addChildFragment(final Fragment fragment, final String fragmentTag, final boolean addToBackStack) {

        /**
         *  initialize child fragment manager
         */
        if (fm == null) fm = getChildFragmentManager();


        /**
          *  Starts a new transaction
         */
        FragmentTransaction ft = fm.beginTransaction();


        /** 
         *  Hide lastly added fragment
         */
        if (backStack != null  && !backStack.isEmpty()) {

            ft.hide(fm.findFragmentByTag(backStack.peek()));

        }

        /** 
         *  Add new fragment
         */
        ft.add(R.id.frag_container, fragment, fragmentTag );


        /**
         *  Add to back stack
         */
         if (addToBackStack) {

            ft.addToBackStack(null);

        }

         /**
         *  Commit transaction
         */
        ft.commit();


        /**
         * Save fragment tag
         */
        if (backStack == null) backStack = new Stack<String>();

            backStack.push(fragmentTag);

    }

    public boolean popFragment() {

        /**
         *  Allow this fragment to consume the back button click
        */
        if (backStack != null   && !backStack.isEmpty()) {

            backStack.pop();

            fragCount-=1;

        }

        return fm != null && fm.popBackStackImmediate();

    }

    @Override
    public boolean backPressed() {

        return popFragment();

    }
}

Answer 1

有人发布了另一个类似的问题，问题是由于 ChildFragmentManager 中的错误。基本上，当子 FragmentManager 从 Activity 中分离时，它最终会以损坏的内部状态结束。看看原来的答案here