PopBackStack导致java.lang.IllegalStateExcoop：无法执行此操作后onSaveInstanceState

Question

我在下面的manager.popbackbackstack行中遇到此错误。有办法解决这个问题吗？事情发生得很顺利。

public void updateView(Fragment fragment) {

        IFragment currentFragment = (IFragment)fragment;

        FragmentManager manager = getSupportFragmentManager();
        FragmentTransaction fragmentTransaction = manager.beginTransaction();
        fragmentTransaction.replace(R.id.content_frame, fragment);

        if(currentFragment != null)
        {
            if(currentFragment.isRoot())
            {
                manager.popBackStack(null, FragmentManager.POP_BACK_STACK_INCLUSIVE);
            }
            else
            {
                fragmentTransaction.addToBackStack("test");
            }
        }

        fragmentTransaction.commitAllowingStateLoss();

        if(drawerManager.DrawerLayout != null) {
            drawerManager.DrawerLayout.closeDrawer(drawerManager.DrawerList);
        }
    }

致命异常：java.lang.IllegalStateException:在android.support.v4.app.FragmentManagerImpl.checkStateLoss（FragmentManager.java:2044）在android.support.v4.app.FragmentManagerImpl.enqueueAction（FragmentManager.java:2067）在android.support.v4.app.FragmentManagerImpl.popBackStack上无法执行此操作com.exposure.activities.EventActivity.setupEvent（EventActivity.java:204）com.exposure.activities.EventActivity.setupEvent（EventActivity.java:204）com.exposure.activities.EventActivity.getData（EventActivity.java:117）com.exposure.utilities.ActivityContainer.getData（ActivityContainer.java:83）android.os.AsyncTask.finish（AsyncTask.java:695）上的com.exposure.utilities.DataTask.onPostExecute（DataTask.java:37）上的android.os.AsyncTask.finish上的android.os.AsyncTask.onPostExecute（DataTask.java:37）上的android.os.Looper.loop（Looper.java:164）上的dispatchMessage（Handler.java:105）上的wrap1（未知源代码）android.app.ActivityThread.main（ActivityThread.java:6938）的java.lang.reflect.Method.invoke（Method.java）的com.android.internal.os.Zygote$methodAndArgscaler.run（Zygote.java:327）的com.android.internal.os.ZygoteInit.main（ZygoteInit.java:1374）

Answer 1

只需调用popBackStackImmediate（），因为常规popBackStack（）是异步的。。。

Answer 2

对我来说，这就是检查片段管理器在popBackStack（）之前是否没有保存状态

if（碎片管理器！=null

Answer 3

如碎片交易中所述

避免在异步回调方法内执行事务。这包括常用的方法，如AsyncTask#onPostExecute（）和LoaderManager.LoaderCallbacks#onLoadFinished（）。在这些方法中执行事务的问题在于，调用它们时，它们不知道活动生命周期的当前状态。

这似乎是您遇到的问题，因为updateView（）是从异步任务调用的，但是让我们测试一下这个假设。

下面的演示应用程序创建一个片段，模拟后台处理和模拟异步回调的回调。代码中有一个标志，mFixIt当设置为true时会导致应用程序正常运行（而不是爆炸），当false让应用程序失败。

使用mFixIt==false。触发器是使应用程序进入停止状态的主页按钮：

以下是堆栈跟踪：

14967-15003 E/AndroidRuntime: FATAL EXCEPTION: Thread-2
    Process: com.example.illegalstatepopbackstack, PID: 14967
    java.lang.IllegalStateException: Can not perform this action after onSaveInstanceState
        at android.support.v4.app.FragmentManagerImpl.checkStateLoss(FragmentManager.java:2080)
        at android.support.v4.app.FragmentManagerImpl.enqueueAction(FragmentManager.java:2106)
        at android.support.v4.app.FragmentManagerImpl.popBackStack(FragmentManager.java:832)
        at com.example.illegalstatepopbackstack.MainActivity.updateView(MainActivity.java:70)
        at com.example.illegalstatepopbackstack.ui.main.MainFragment$1.run(MainFragment.java:63)
        at java.lang.Thread.run(Thread.java:764)

现在使用mFixIt==true。这次的不同之处在于，当活动处于停止状态时，应用程序识别异步回调，记录已发生的情况，并在应用程序重新启动时完成处理。视觉系统只需按下home（主页）按钮并从“最近”恢复即可。应用程序只需在开始时放置片段，重新启动时会更改顶部的TextView文本，并从后台弹出片段。

可以看出，处理按预期完成。

这是一个微不足道的例子。如果您的处理更复杂，或者您只是想要一种更正式的方式来处理这种情况，我建议您看看这个解决方案。

以下是演示应用程序的代码：

MainActivity.java

public class MainActivity extends AppCompatActivity {
    // Set to true to fix the problem; false will cause the IllegalStateException
    private boolean mFixIt = false;

    private MainFragment mFragment;
    private TextView mTextView;
    private boolean mIsPaused;
    private boolean mUpdateViewNeeded;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main_activity);
        mTextView = findViewById(R.id.textView);

        FragmentManager fm = getSupportFragmentManager();
        if (savedInstanceState == null) {
            // Create out fragment
            mFragment = MainFragment.newInstance();
            fm.beginTransaction()
                .replace(R.id.container, mFragment)
                .addToBackStack(FRAGMENT_TAG)
                .commit();
        } else {
            // Find the restored fragment.
            mFragment = (MainFragment) fm.findFragmentByTag(FRAGMENT_TAG);
        }
    }

    @Override
    protected void onStop() {
        super.onStop();

        // Simulate a background task that does something useful. This one just waits a few
        // second then does a callback to updateView(). The activity will be fully paused by then.
        mFragment.doSomethingInBackground();
        mIsPaused = true;
        Log.d("MainActivity","<<<< stopped");
    }

    @Override
    protected void onStart() {
        super.onStart();
        mIsPaused = false;
        if (mUpdateViewNeeded) {
            // Execute delayed processing now that the activity is resumed.
            updateView(getSupportFragmentManager().findFragmentByTag(FRAGMENT_TAG));
        }
    }

    public void updateView(Fragment fragment) {
        if (mIsPaused && mFixIt) {
            // Delay processing
            mUpdateViewNeeded = true;
        } else {
            // Do out update work. If we are paused, this will get an IllegalStateException. If
            // we are resumed, this will work as intended.
            mTextView.setText("Replaced...");
            getSupportFragmentManager().popBackStack(null, FragmentManager.POP_BACK_STACK_INCLUSIVE);
            mUpdateViewNeeded = false;
        }
    }

    public static final String FRAGMENT_TAG = "MyFragment";
}

MainFragment.java

public class MainFragment extends Fragment {

    MainActivity mMainActivity;

    public static MainFragment newInstance() {
        return new MainFragment();
    }

    @Nullable
    @Override
    public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container,
                             @Nullable Bundle savedInstanceState) {
        return inflater.inflate(R.layout.main_fragment, container, false);
    }

    @Override
    public void onActivityCreated(@Nullable Bundle savedInstanceState) {
        super.onActivityCreated(savedInstanceState);
    }

    @Override
    public void onAttach(Context context) {
        super.onAttach(context);
        mMainActivity = (MainActivity) context;
    }

    @Override
    public void onDetach() {
        super.onDetach();
        mMainActivity = null;
    }

    @Override
    public void onStart() {
        super.onStart();

    }

    public void doSomethingInBackground() {
        new Thread(new Runnable() {
            @Override
            public void run() {
                try {
                    Thread.sleep(2000);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
                if (mMainActivity != null) {
                    mMainActivity.updateView(MainFragment.this);
                }
            }
        }).start();
    }
}

main_activity.xml

<TextView
    android:id="@+id/textView"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:background="@android:color/holo_blue_light"
    android:gravity="center"
    android:text="To be replaced..."
    android:textSize="36sp"
    android:textStyle="bold" />

<FrameLayout
    android:id="@+id/container"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity" />

main_fragment.xml

<android.support.constraint.ConstraintLayout 
    android:id="@+id/main"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="@android:color/holo_green_light"
    tools:context=".ui.main.MainFragment">

    <TextView
        android:id="@+id/message"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="MainFragment"
        android:textSize="36sp"
        android:textStyle="bold"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

</android.support.constraint.ConstraintLayout>