Lang.IllegalStateException: 在 onSaveInstanceState 之后无法执行此操作

我正在使用应用程序的支持库。在我的片段活动中，我使用 AsyncTask 从互联网上下载数据。在 onPreExecute ()方法中，我添加了一个片段，在 onPostExecute ()方法中，我再次删除了它。当方向在两者之间改变时，我得到上面提到的异常。请看详情:

private class onFriendAddedAsyncTask extends AsyncTask<String, Void, String> {
DummyFragment dummyFragment;
FragmentManager fm;
FragmentTransaction ft;


@Override
protected void onPreExecute() {
Log.v("MyFragmentActivity", "onFriendAddedAsyncTask/onPreExecute");
dummyFragment = DummyFragment.newInstance();
fm = getSupportFragmentManager();
ft = fm.beginTransaction();
ft.add(dummyFragment, "dummy_fragment");
ft.commit();
}


@Override
protected void onPostExecute(String result) {
Log.v("MyFragmentActivity", "onFriendAddedAsyncTask/onPostExecute");
ft = fm.beginTransaction();
ft.remove(dummyFragment);
ft.commit();
}


@Override
protected String doInBackground(String... name) {
Log.v("MyFragmentActivity", "onFriendAddedAsyncTask/doInBackground");
...
}

我得到了以下 LogCut:

01-05 23:54:19.958: V/MyFragmentActivity(12783): onFriendAddedAsyncTask/onPreExecute
01-05 23:54:19.968: V/DummyFragment(12783): onAttach
01-05 23:54:19.968: V/DummyFragment(12783): onCreate
01-05 23:54:19.968: V/MyFragmentActivity(12783): onFriendAddedAsyncTask/doInBackground
01-05 23:54:19.973: V/DummyFragment(12783): onCreateView
01-05 23:54:19.973: V/DummyFragment(12783): onActivityCreated
01-05 23:54:19.973: V/DummyFragment(12783): onStart
01-05 23:54:19.973: V/DummyFragment(12783): onResume
01-05 23:54:21.933: V/MyFragmentActivity(12783): onSaveInstanceState
01-05 23:54:21.933: V/DummyFragment(12783): onSaveInstanceState
01-05 23:54:21.933: V/MyFragmentActivity(12783): onPause
01-05 23:54:21.933: V/DummyFragment(12783): onPause
01-05 23:54:21.938: V/MyFragmentActivity(12783): onStop
01-05 23:54:21.938: V/DummyFragment(12783): onStop
01-05 23:54:21.938: V/MyFragmentActivity(12783): onDestroy
01-05 23:54:21.938: V/DummyFragment(12783): onDestroyView
01-05 23:54:21.938: V/DummyFragment(12783): onDestroy
01-05 23:54:21.938: V/DummyFragment(12783): onDetach
01-05 23:54:21.978: V/MyFragmentActivity(12783): onCreate
01-05 23:54:21.978: V/DummyFragment(12783): onAttach
01-05 23:54:21.978: V/DummyFragment(12783): onCreate
01-05 23:54:22.263: V/MyFragmentActivity(12783): onStart
01-05 23:54:22.313: V/DummyFragment(12783): onCreateView
01-05 23:54:22.313: V/DummyFragment(12783): onActivityCreated
01-05 23:54:22.313: V/DummyFragment(12783): onStart
01-05 23:54:22.323: V/MyFragmentActivity(12783): onResume
01-05 23:54:22.323: V/MyFragmentActivity(12783): onPostResume
01-05 23:54:22.323: V/MyFragmentActivity(12783): onResumeFragments
01-05 23:54:22.323: V/DummyFragment(12783): onResume
01-05 23:54:27.123: V/MyFragmentActivity(12783): onFriendAddedAsyncTask/onPostExecute
01-05 23:54:27.123: D/AndroidRuntime(12783): Shutting down VM
01-05 23:54:27.123: W/dalvikvm(12783): threadid=1: thread exiting with uncaught exception (group=0x4001d7d0)
01-05 23:54:27.138: E/AndroidRuntime(12783): FATAL EXCEPTION: main
01-05 23:54:27.138: E/AndroidRuntime(12783): java.lang.IllegalStateException: Can not perform this action after onSaveInstanceState
01-05 23:54:27.138: E/AndroidRuntime(12783):    at android.support.v4.app.FragmentManagerImpl.checkStateLoss(FragmentManager.java:1314)
01-05 23:54:27.138: E/AndroidRuntime(12783):    at android.support.v4.app.FragmentManagerImpl.enqueueAction(FragmentManager.java:1325)
01-05 23:54:27.138: E/AndroidRuntime(12783):    at android.support.v4.app.BackStackRecord.commitInternal(BackStackRecord.java:548)
01-05 23:54:27.138: E/AndroidRuntime(12783):    at android.support.v4.app.BackStackRecord.commit(BackStackRecord.java:532)
01-05 23:54:27.138: E/AndroidRuntime(12783):    at com.xyz.dummy.MyFragmentActivity$onFriendAddedAsyncTask.onPostExecute(MyFragmentActivity.java:447)
01-05 23:54:27.138: E/AndroidRuntime(12783):    at com.xyz.dummy.MyFragmentActivity$onFriendAddedAsyncTask.onPostExecute(MyFragmentActivity.java:1)
01-05 23:54:27.138: E/AndroidRuntime(12783):    at android.os.AsyncTask.finish(AsyncTask.java:417)
01-05 23:54:27.138: E/AndroidRuntime(12783):    at android.os.AsyncTask.access$300(AsyncTask.java:127)
01-05 23:54:27.138: E/AndroidRuntime(12783):    at android.os.AsyncTask$InternalHandler.handleMessage(AsyncTask.java:429)
01-05 23:54:27.138: E/AndroidRuntime(12783):    at android.os.Handler.dispatchMessage(Handler.java:99)
01-05 23:54:27.138: E/AndroidRuntime(12783):    at android.os.Looper.loop(Looper.java:123)
01-05 23:54:27.138: E/AndroidRuntime(12783):    at android.app.ActivityThread.main(ActivityThread.java:4627)
01-05 23:54:27.138: E/AndroidRuntime(12783):    at java.lang.reflect.Method.invokeNative(Native Method)
01-05 23:54:27.138: E/AndroidRuntime(12783):    at java.lang.reflect.Method.invoke(Method.java:521)
01-05 23:54:27.138: E/AndroidRuntime(12783):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:858)
01-05 23:54:27.138: E/AndroidRuntime(12783):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
01-05 23:54:27.138: E/AndroidRuntime(12783):    at dalvik.system.NativeStart.main(Native Method)

在关于类似问题的其他线程中，原因似乎是在调用 onResume ()方法之前调用了 onPostExecute 方法。但是即使之前调用了 onResume () ，我还是得到了异常。

有人知道出什么事了吗？

活动内容如下:

public class MyFragmentActivity extends FragmentActivity implements OnFriendSelectedListener, OnFriendAddedListener, OnFriendOptionSelectedListener, LoaderCallbacks<Cursor> {


@Override
public void onCreate(Bundle savedInstanceState) {
Log.v("MyFragmentActivity", "onCreate");
super.onCreate(savedInstanceState);
setContentView(R.layout.fragment_activity_layout);
FragmentManager fm = getSupportFragmentManager();
FragmentTransaction ft = fm.beginTransaction();
FriendListFragment friendListFragment = (FriendListFragment)fm.findFragmentById(R.id.friend_list_fragment_layout);
if (friendListFragment == null) {
friendListFragment = new FriendListFragment();
ft.add(R.id.friend_list_fragment_layout, friendListFragment);
ft.commit();
fm.executePendingTransactions();
startService(new Intent(this, MyIntentService.class));
getSupportLoaderManager().initLoader(CHECK_EMPTY_DATABASE, null, this);
}
}


@Override
public boolean onCreateOptionsMenu(Menu menu) {
super.onCreateOptionsMenu(menu);
getMenuInflater().inflate(R.menu.fragment_activity_options_menu, menu);
return true;
}


@Override
public boolean onOptionsItemSelected(MenuItem item) {
super.onOptionsItemSelected(item);
switch (item.getItemId()) {
case R.id.add_friend_menu_item:
AddFriendDialogFragment addFriendDialogFragment = AddFriendDialogFragment.newInstance();
addFriendDialogFragment.show(getSupportFragmentManager(), "add_friend_dialog_fragment");
return true;
default:
return false;
}
}


@Override
public void onFriendAdded(String name) {
name = name.trim();
if (name.length() > 0) {
new onFriendAddedAsyncTask().execute(name);
}
}

当使用 commAllowingStateloss ()时，我得到以下异常:

01-06 14:54:29.548: E/AndroidRuntime(18020): FATAL EXCEPTION: main
01-06 14:54:29.548: E/AndroidRuntime(18020): java.lang.IllegalStateException: Activity has been destroyed
01-06 14:54:29.548: E/AndroidRuntime(18020):    at android.support.v4.app.FragmentManagerImpl.enqueueAction(FragmentManager.java:1329)
01-06 14:54:29.548: E/AndroidRuntime(18020):    at android.support.v4.app.BackStackRecord.commitInternal(BackStackRecord.java:548)
01-06 14:54:29.548: E/AndroidRuntime(18020):    at android.support.v4.app.BackStackRecord.commitAllowingStateLoss(BackStackRecord.java:536)
01-06 14:54:29.548: E/AndroidRuntime(18020):    at com.xyz.dummy.FadiaFragmentActivity$onFriendAddedAsyncTask.onPostExecute(FadiaFragmentActivity.java:461)
01-06 14:54:29.548: E/AndroidRuntime(18020):    at com.xyz.dummy.FadiaFragmentActivity$onFriendAddedAsyncTask.onPostExecute(FadiaFragmentActivity.java:1)
01-06 14:54:29.548: E/AndroidRuntime(18020):    at android.os.AsyncTask.finish(AsyncTask.java:417)
01-06 14:54:29.548: E/AndroidRuntime(18020):    at android.os.AsyncTask.access$300(AsyncTask.java:127)
01-06 14:54:29.548: E/AndroidRuntime(18020):    at android.os.AsyncTask$InternalHandler.handleMessage(AsyncTask.java:429)
01-06 14:54:29.548: E/AndroidRuntime(18020):    at android.os.Handler.dispatchMessage(Handler.java:99)
01-06 14:54:29.548: E/AndroidRuntime(18020):    at android.os.Looper.loop(Looper.java:123)
01-06 14:54:29.548: E/AndroidRuntime(18020):    at android.app.ActivityThread.main(ActivityThread.java:4627)
01-06 14:54:29.548: E/AndroidRuntime(18020):    at java.lang.reflect.Method.invokeNative(Native Method)
01-06 14:54:29.548: E/AndroidRuntime(18020):    at java.lang.reflect.Method.invoke(Method.java:521)
01-06 14:54:29.548: E/AndroidRuntime(18020):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:858)
01-06 14:54:29.548: E/AndroidRuntime(18020):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
01-06 14:54:29.548: E/AndroidRuntime(18020):    at dalvik.system.NativeStart.main(Native Method)

如下所示，当我实现 AsynTask 时，我得到相同的 IllegalStateExeption，因为 findFragmentById ()方法返回空指针。

private class onFriendAddedAsyncTask extends AsyncTask<String, Void, String> {


protected void onPreExecute() {
Log.v("MyFragmentActivity", "onFriendAddedAsyncTask/onPreExecute");
FragmentManager fm = getSupportFragmentManager();
FragmentTransaction ft = fm.beginTransaction();
DummyFragment dummyFragment = DummyFragment.newInstance();
ft.add(R.id.dummy_fragment_layout, dummyFragment);
ft.commit();
}


protected void onPostExecute(String result) {
Log.v("MyFragmentActivity", "onFriendAddedAsyncTask/onPostExecute");
FragmentManager fm = getSupportFragmentManager();
FragmentTransaction ft = fm.beginTransaction();
DummyFragment dummyFragment = (DummyFragment) fm.findFragmentById(R.id.dummy_fragment_layout);
ft.remove(dummyFragment);
ft.commitAllowingStateLoss();
}

在下一步中，我使用一个处理程序来添加和删除 DummyFragment。此外，我还添加了一些调试输出。

private class onFriendAddedAsyncTask extends AsyncTask<String, Void, String> {


@Override
protected void onPreExecute() {
Log.v("MyFragmentActivity", "onFriendAddedAsyncTask/onPreExecute " + getSupportFragmentManager());
Log.v("MyFragmentActivity", "onFriendAddedAsyncTask/onPreExecute " + getSupportFragmentManager().findFragmentById(R.id.dummy_fragment_layout));
Log.v("MyFragmentActivity", "onFriendAddedAsyncTask/onPreExecute " + getSupportFragmentManager().findFragmentById(R.id.friend_list_fragment_layout));


new Handler().post(new Runnable() {
public void run() {
Log.v("MyFragmentActivity", "onFriendAddedAsyncTask/onPreExecute " + getSupportFragmentManager());
Log.v("MyFragmentActivity", "onFriendAddedAsyncTask/onPreExecute " + getSupportFragmentManager().findFragmentById(R.id.dummy_fragment_layout));
Log.v("MyFragmentActivity", "onFriendAddedAsyncTask/onPreExecute " + getSupportFragmentManager().findFragmentById(R.id.friend_list_fragment_layout));
FragmentManager fm = getSupportFragmentManager();
FragmentTransaction ft = fm.beginTransaction();
DummyFragment dummyFragment = DummyFragment.newInstance();
ft.add(R.id.dummy_fragment_layout, dummyFragment);
ft.commit();
}
});


@Override
protected void onPostExecute(String result) {
Log.v("MyFragmentActivity", "onFriendAddedAsyncTask/onPostExecute " + getSupportFragmentManager());
Log.v("MyFragmentActivity", "onFriendAddedAsyncTask/onPostExecute " + getSupportFragmentManager().findFragmentById(R.id.dummy_fragment_layout));
Log.v("MyFragmentActivity", "onFriendAddedAsyncTask/onPostExecute " + getSupportFragmentManager().findFragmentById(R.id.friend_list_fragment_layout));


new Handler().post(new Runnable() {
public void run() {
Log.v("MyFragmentActivity", "onFriendAddedAsyncTask/onPostExecute " + getSupportFragmentManager());
Log.v("MyFragmentActivity", "onFriendAddedAsyncTask/onPostExecute " + getSupportFragmentManager().findFragmentById(R.id.dummy_fragment_layout));
Log.v("MyFragmentActivity", "onFriendAddedAsyncTask/onPostExecute " + getSupportFragmentManager().findFragmentById(R.id.friend_list_fragment_layout));
FragmentManager fm = getSupportFragmentManager();
FragmentTransaction ft = fm.beginTransaction();
DummyFragment dummyFragment = (DummyFragment) fm.findFragmentById(R.id.dummy_fragment_layout);
ft.remove(dummyFragment);
ft.commitAllowingStateLoss();
}
});

我得到了以下 LogCut:

01-07 19:00:17.273: V/MyFragmentActivity(4124): onFriendAddedAsyncTask/onPreExecute FragmentManager{45e384a8 in MyFragmentActivity{45e38358}}
01-07 19:00:17.273: V/MyFragmentActivity(4124): onFriendAddedAsyncTask/onPreExecute null
01-07 19:00:17.273: V/MyFragmentActivity(4124): onFriendAddedAsyncTask/onPreExecute FriendListFragment{45e38ab0 #0 id=0x7f0a0002}
01-07 19:00:17.283: V/MyFragmentActivity(4124): onFriendAddedAsyncTask/onPreExecute FragmentManager{45e384a8 in MyFragmentActivity{45e38358}}
01-07 19:00:17.288: V/MyFragmentActivity(4124): onFriendAddedAsyncTask/doInBackground
01-07 19:00:17.288: V/MyFragmentActivity(4124): onFriendAddedAsyncTask/onPreExecute null
01-07 19:00:17.288: V/MyFragmentActivity(4124): onFriendAddedAsyncTask/onPreExecute FriendListFragment{45e38ab0 #0 id=0x7f0a0002}
01-07 19:00:17.308: V/DummyFragment(4124): onAttach DummyFragment{45dd7498 #2 id=0x7f0a0004}
01-07 19:00:17.308: V/DummyFragment(4124): onCreate DummyFragment{45dd7498 #2 id=0x7f0a0004}
01-07 19:00:17.308: V/DummyFragment(4124): onCreateView DummyFragment{45dd7498 #2 id=0x7f0a0004}
01-07 19:00:17.308: V/DummyFragment(4124): onActivityCreated DummyFragment{45dd7498 #2 id=0x7f0a0004}
01-07 19:00:17.308: V/DummyFragment(4124): onStart DummyFragment{45dd7498 #2 id=0x7f0a0004}
01-07 19:00:17.313: V/DummyFragment(4124): onResume DummyFragment{45dd7498 #2 id=0x7f0a0004}
01-07 19:00:18.098: V/MyFragmentActivity(4124): onSaveInstanceState DummyFragment{45dd7498 #2 id=0x7f0a0004}
01-07 19:00:18.098: V/DummyFragment(4124): onSaveInstanceState DummyFragment{45dd7498 #2 id=0x7f0a0004}
01-07 19:00:18.098: V/MyFragmentActivity(4124): onPause DummyFragment{45dd7498 #2 id=0x7f0a0004}
01-07 19:00:18.098: V/DummyFragment(4124): onPause DummyFragment{45dd7498 #2 id=0x7f0a0004}
01-07 19:00:18.103: V/MyFragmentActivity(4124): onStop DummyFragment{45dd7498 #2 id=0x7f0a0004}
01-07 19:00:18.103: V/DummyFragment(4124): onStop DummyFragment{45dd7498 #2 id=0x7f0a0004}
01-07 19:00:18.103: V/MyFragmentActivity(4124): onDestroy DummyFragment{45dd7498 #2 id=0x7f0a0004}
01-07 19:00:18.103: V/DummyFragment(4124): onDestroyView DummyFragment{45dd7498 #2 id=0x7f0a0004}
01-07 19:00:18.108: V/DummyFragment(4124): onDestroy DummyFragment{45dd7498 #2 id=0x7f0a0004}
01-07 19:00:18.113: V/DummyFragment(4124): onDetach DummyFragment{45dd7498 #2 id=0x7f0a0004}
01-07 19:00:18.138: V/MyFragmentActivity(4124): onCreate
01-07 19:00:18.138: V/FriendListFragment(4124): FriendListFragment
01-07 19:00:18.138: V/FriendListFragment(4124): onAttach FriendListFragment{45e4a7f8 #0 id=0x7f0a0002}
01-07 19:00:18.138: V/FriendListFragment(4124): onCreate FriendListFragment{45e4a7f8 #0 id=0x7f0a0002}
01-07 19:00:18.148: V/DummyFragment(4124): onAttach DummyFragment{45d7d1a0 #2 id=0x7f0a0004}
01-07 19:00:18.153: V/DummyFragment(4124): onCreate DummyFragment{45d7d1a0 #2 id=0x7f0a0004}
01-07 19:00:18.523: V/MyFragmentActivity(4124): onStart DummyFragment{45d7d1a0 #2 id=0x7f0a0004}
01-07 19:00:18.543: V/FriendListFragment(4124): onActivityCreated FriendListFragment{45e4a7f8 #0 id=0x7f0a0002}
01-07 19:00:18.548: V/DummyFragment(4124): onCreateView DummyFragment{45d7d1a0 #2 id=0x7f0a0004}
01-07 19:00:18.548: V/DummyFragment(4124): onActivityCreated DummyFragment{45d7d1a0 #2 id=0x7f0a0004}
01-07 19:00:18.548: V/FriendListFragment(4124): onLoadFinished FragmentManager{45d8e478 in MyFragmentActivity{45e4a6d8}}
01-07 19:00:18.548: V/FriendListFragment(4124): onLoadFinished FriendListFragment{45e4a7f8 #0 id=0x7f0a0002}
01-07 19:00:18.553: V/DummyFragment(4124): onStart DummyFragment{45d7d1a0 #2 id=0x7f0a0004}
01-07 19:00:18.553: V/FriendListFragment(4124): onLoadFinished FragmentManager{45d8e478 in MyFragmentActivity{45e4a6d8}}
01-07 19:00:18.553: V/FriendListFragment(4124): onLoadFinished FriendListFragment{45e4a7f8 #0 id=0x7f0a0002}
01-07 19:00:18.558: V/MyFragmentActivity(4124): onResume DummyFragment{45d7d1a0 #2 id=0x7f0a0004}
01-07 19:00:18.558: V/MyFragmentActivity(4124): onPostResume DummyFragment{45d7d1a0 #2 id=0x7f0a0004}
01-07 19:00:18.558: V/MyFragmentActivity(4124): onResumeFragments DummyFragment{45d7d1a0 #2 id=0x7f0a0004}
01-07 19:00:18.558: V/FriendListFragment(4124): onResume FriendListFragment{45e4a7f8 #0 id=0x7f0a0002}
01-07 19:00:18.563: V/FriendListFragment(4124): onCreateLoader FriendListFragment{45e4a7f8 #0 id=0x7f0a0002}
01-07 19:00:18.563: V/DummyFragment(4124): onResume DummyFragment{45d7d1a0 #2 id=0x7f0a0004}
01-07 19:00:18.723: V/FriendListFragment(4124): onLoadFinished FragmentManager{45d8e478 in MyFragmentActivity{45e4a6d8}}
01-07 19:00:18.723: V/FriendListFragment(4124): onLoadFinished FriendListFragment{45e4a7f8 #0 id=0x7f0a0002}
01-07 19:00:18.893: V/MyFragmentActivity(4124): onFriendAddedAsyncTask/onPostExecute FragmentManager{45e384a8 in null}}
01-07 19:00:18.893: V/MyFragmentActivity(4124): onFriendAddedAsyncTask/onPostExecute null
01-07 19:00:18.893: V/MyFragmentActivity(4124): onFriendAddedAsyncTask/onPostExecute null
01-07 19:00:18.923: V/MyFragmentActivity(4124): onFriendAddedAsyncTask/onPostExecute FragmentManager{45e384a8 in null}}
01-07 19:00:18.923: V/MyFragmentActivity(4124): onFriendAddedAsyncTask/onPostExecute null
01-07 19:00:18.923: V/MyFragmentActivity(4124): onFriendAddedAsyncTask/onPostExecute null
01-07 19:00:18.928: D/AndroidRuntime(4124): Shutting down VM
01-07 19:00:18.928: W/dalvikvm(4124): threadid=1: thread exiting with uncaught exception (group=0x4001d7d0)
01-07 19:00:18.938: E/AndroidRuntime(4124): FATAL EXCEPTION: main
01-07 19:00:18.938: E/AndroidRuntime(4124): java.lang.IllegalStateException: Activity has been destroyed
01-07 19:00:18.938: E/AndroidRuntime(4124):     at android.support.v4.app.FragmentManagerImpl.enqueueAction(FragmentManager.java:1329)
01-07 19:00:18.938: E/AndroidRuntime(4124):     at android.support.v4.app.BackStackRecord.commitInternal(BackStackRecord.java:548)
01-07 19:00:18.938: E/AndroidRuntime(4124):     at android.support.v4.app.BackStackRecord.commitAllowingStateLoss(BackStackRecord.java:536)
01-07 19:00:18.938: E/AndroidRuntime(4124):     at com.xyz.dummy.MyFragmentActivity$onFriendAddedAsyncTask$2.run(MyFragmentActivity.java:476)
01-07 19:00:18.938: E/AndroidRuntime(4124):     at android.os.Handler.handleCallback(Handler.java:587)
01-07 19:00:18.938: E/AndroidRuntime(4124):     at android.os.Handler.dispatchMessage(Handler.java:92)
01-07 19:00:18.938: E/AndroidRuntime(4124):     at android.os.Looper.loop(Looper.java:123)
01-07 19:00:18.938: E/AndroidRuntime(4124):     at android.app.ActivityThread.main(ActivityThread.java:4627)
01-07 19:00:18.938: E/AndroidRuntime(4124):     at java.lang.reflect.Method.invokeNative(Native Method)
01-07 19:00:18.938: E/AndroidRuntime(4124):     at java.lang.reflect.Method.invoke(Method.java:521)
01-07 19:00:18.938: E/AndroidRuntime(4124):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:858)
01-07 19:00:18.938: E/AndroidRuntime(4124):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
01-07 19:00:18.938: E/AndroidRuntime(4124):     at dalvik.system.NativeStart.main(Native Method)

在 onPreExecute ()中，FriendListFragment 的 id = 0x7f0a0002。在处理程序内部，用 id = 0x7f0a0004创建 DummyFragment。在 onPostExecute ()中，两个 ID 都为空。 在 onPreExecute ()中，MyFragmentActivity 的地址是45e38358。但是在 onPostExecute ()中它是 null。但是在这两种方法中，FragmentManager 地址都是45e384a8。 我想 onPostExecute 使用了一个无效的片段管理器。但是为什么呢？

177517 次浏览
小开
最佳答案

你应按以下方式以 Handler进行交易:

@Override
protected void onPostExecute(String result) {
Log.v("MyFragmentActivity", "onFriendAddedAsyncTask/onPostExecute");
new Handler().post(new Runnable() {
public void run() {
fm = getSupportFragmentManager();
ft = fm.beginTransaction();
ft.remove(dummyFragment);
ft.commit();
}
});
}
小开

出现异常的原因是在 AsyncTask运行期间重新创建了 FragmentActivity，然后在 onPostExecute()中访问了之前被破坏的 FragmentActivity。

问题是要获得对新 FragmentActivity的有效引用。没有这样的方法，既没有 getActivity()也没有 findById()或类似的东西。这个论坛充满了针对这个问题的帖子(例如搜索 "Activity context in onPostExecute")。其中一些描述了变通方法(直到现在我还没有找到一个好的)。

也许为了我的目的使用服务会是一个更好的解决方案。

小开

谢谢 Oleg Vaskevich。使用 FragmentActivity的 WeakReference解决了这个问题。我的代码现在看起来如下:

public class MyFragmentActivity extends FragmentActivity implements OnFriendAddedListener {


private static WeakReference<MyFragmentActivity> wrActivity = null;


@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
wrActivity = new WeakReference<MyFragmentActivity>(this);
...


private class onFriendAddedAsyncTask extends AsyncTask<String, Void, String> {


@Override
protected void onPreExecute() {
FragmentManager fm = getSupportFragmentManager();
FragmentTransaction ft = fm.beginTransaction();
DummyFragment dummyFragment = DummyFragment.newInstance();
ft.add(R.id.dummy_fragment_layout, dummyFragment);
ft.commit();
}


@Override
protected void onPostExecute(String result) {
final Activity activity = wrActivity.get();
if (activity != null && !activity.isFinishing()) {
FragmentManager fm = activity.getSupportFragmentManager();
FragmentTransaction ft = fm.beginTransaction();
DummyFragment dummyFragment = (DummyFragment) fm.findFragmentById(R.id.dummy_fragment_layout);
ft.remove(dummyFragment);
ft.commitAllowingStateLoss();
}
}
小开

不管怎样，我在一个在后台运行服务的应用程序上出现了这个错误。在其中一个对话框中，必须向用户显示超时对话框。如果应用程序不再在前台运行，这个对话框就是导致这个错误的原因。

在我们的例子中，显示对话框在应用程序处于后台时没有用，所以我们只是跟踪它(布尔值标记为 Pauze en onResume) ，然后只在应用程序对用户可见时才显示对话框。

小开

我相信这个问题的正确答案是下面的方法。

public abstract int commitAllowingStateLoss ()

类似于 commit () ，但是允许在活动的 状态保存。这是危险的，因为如果 活动需要稍后从其状态中恢复，因此这应该 只能在 UI 状态可以改变的情况下使用 意外地对用户。

上述描述与此方法有关。

protected void onSaveInstanceState(android.os.Bundle outState)

这个问题恰好发生在设备进入睡眠状态时。

Http://developer.android.com/reference/android/app/fragmenttransaction.html

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这种情况发生在我身上，因为我正在从泄漏活动的子片段调用 commit()。它将 Activity 作为一个属性保留，并且在一个旋转活动变量上没有被 onAttach();更新，因此我试图通过保留 (setRetainInstance(true);)片段来提交僵尸 Activity 上的事务。

小开

我有一个类似的问题，通过将一些片段事务代码从 onResume()移动到 onStart()，我解决了这个问题。

更准确地说: 我的应用程序是一个发射器。按下 Android Home 按钮后，用户可以选择一个启动器，直到他/她的决定被记住。当在这一点“返回”时(例如点击灰色区域) ，应用程序崩溃了。

也许这对某人有帮助。

小开

简短有效的解决方案:

遵循简单的步骤:

步骤1 : 在相应的片段中重写 onSaveInstanceState状态，并删除其中的 super 方法。

@Override
public void onSaveInstanceState(Bundle outState) {
}

步骤2 : 在进行片段操作时使用 CommitAllowingStateLoss();而不是 commit();。

fragmentTransaction.commitAllowingStateLoss();
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在显示片段之前检查活动 isFinishing()。

例如:

if(!isFinishing()) {
FragmentManager fm = getSupportFragmentManager();
FragmentTransaction ft = fm.beginTransaction();
DummyFragment dummyFragment = DummyFragment.newInstance();
ft.add(R.id.dummy_fragment_layout, dummyFragment);
ft.commitAllowingStateLoss();
}
小开

我的应用程序有一个片段加载3秒钟，但当第一个屏幕准备显示，我按下主页按钮，恢复运行它，它显示相同的错误，所以它编辑我的代码，它运行得非常顺利:

new Handler().post(new Runnable() {
public void run() {
if (saveIns == null) {
mFragment = new Fragment_S1_loading();
getFragmentManager().beginTransaction()
.replace(R.id.container, mFragment).commit();
}
getActionBar().hide();
// Loading screen in 3 secs:
mCountDownTimerLoading = new CountDownTimer(3000, 1000) {


@Override
public void onTick(long millisUntilFinished) {


}


@Override
public void onFinish() {
if (saveIns == null) {// TODO bug when start app and press home
// button
getFragmentManager()
.beginTransaction()
.replace(R.id.container,
new Fragment_S2_sesstion1()).commitAllowingStateLoss();
}
getActionBar().show();
}
}.start();
}
});

注意: 添加 committee AllowingStateloss ()而不是 commit ()

小开

解决方案1: 重写 onSaveInstanceState()并删除其中的超级调用。

@Override
public void onSaveInstanceState(Bundle outState) {
}

解决方案2: 覆盖 onSaveInstanceState()并在超级调用之前删除您的片段

@Override
public void onSaveInstanceState(Bundle outState) {
// TODO: Add code to remove fragment here
super.onSaveInstanceState(outState);
}
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从支持库24.0.0版开始，您可以调用同步提交此事务的 FragmentTransaction.commitNow()方法，而不是先调用 commit()，然后调用 executePendingTransactions()

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当一个进程试图操纵其 onStop()已被调用的活动时，就会发生这个问题。它不一定要绑定到片段事务，也可以绑定到其他方法，比如 onBackPress ()。

除了 AsyncTask 之外，此类问题的另一个来源是总线模式的订阅错位。通常，事件总线或 RxBus 的订阅在 Activity 的 onCreate 期间注册，并在 onDestroy 中注销。如果一个新的 Activity 启动并发布了一个被订阅者从前一个 Activity 截获的事件，那么它可能会产生这个错误。如果发生这种情况，那么一种解决方案是将订阅注册和注销移动到 onStart()和 onStop()。

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有一个替代的解决方案(不是最好的解决方案)这个问题，但工程。使用标志您可以处理它，如下所示

/**
* Flag to avoid "java.lang.IllegalStateException: Can not perform this action after
* onSaveInstanceState". Avoid Fragment transaction until onRestoreInstanceState or onResume
* gets called.
*/
private boolean isOnSaveInstanceStateCalled = false;




@Override
public void onRestoreInstanceState(final Bundle bundle) {
.....
isOnSaveInstanceStateCalled = false;
.....
}


@Override
public void onSaveInstanceState(final Bundle outState) {
.....
isOnSaveInstanceStateCalled = true;
.....
}


@Override
public void onResume() {
super.onResume();
isOnSaveInstanceStateCalled = false;
.....
}

您可以在执行片段事务时检查这个 boolean值。

private void fragmentReplace(Fragment fragment, String fragmentTag){
if (!isOnSaveInstanceStateCalled) {
getSupportFragmentManager()
.beginTransaction()
.replace(R.id.layout_container, fragment, fragmentTag)
.commit();
}
}
小开

使用 commitAllowingStateLoss()代替 commit()。

当您使用 commit()时，如果发生状态丢失，它会抛出异常，但是 commitAllowingStateLoss()保存事务时没有状态丢失，所以如果发生状态丢失，它不会抛出异常。

小开

如果在活动失去状态后提交任何片段事务，则会遇到 IllegalStateException-Activity 不在前台。当您尝试在 AsyncTask 中提交任何片段或在网络请求之后提交片段时，通常会遇到这种情况。

为了避免这种崩溃，您只需要延迟任何片段事务，直到恢复活动状态。下面是如何做到这一点

声明两个私有布尔变量

public class MainActivity extends AppCompatActivity {


//Boolean variable to mark if the transaction is safe
private boolean isTransactionSafe;


//Boolean variable to mark if there is any transaction pending
private boolean isTransactionPending;

现在，在 onPostResume ()和 onPuse 中，我们设置和取消布尔变量 isTransactionSafe。想法是标记交易安全，只有当活动在前台，所以没有国家的机会。

/*
onPostResume is called only when the activity's state is completely restored. In this we will
set our boolean variable to true. Indicating that transaction is safe now
*/
public void onPostResume(){
super.onPostResume();
isTransactionSafe=true;
}
/*
onPause is called just before the activity moves to background and also before onSaveInstanceState. In this
we will mark the transaction as unsafe
*/


public void onPause(){
super.onPause();
isTransactionSafe=false;


}


private void commitFragment(){
if(isTransactionSafe) {
MyFragment myFragment = new MyFragment();
FragmentManager fragmentManager = getFragmentManager();
FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();
fragmentTransaction.add(R.id.frame, myFragment);
fragmentTransaction.commit();
}
}

我们到目前为止所做的将会从 IllegalStateException 中保存，但是如果在活动移动到后台之后完成事务，那么它们将会丢失，有点像 commAllowStateloss ()。为了帮助解决这个问题，我们使用 isTransactionPending 布尔变量

public void onPostResume(){
super.onPostResume();
isTransactionSafe=true;
/* Here after the activity is restored we check if there is any transaction pending from
the last restoration
*/
if (isTransactionPending) {
commitFragment();
}
}




private void commitFragment(){


if(isTransactionSafe) {
MyFragment myFragment = new MyFragment();
FragmentManager fragmentManager = getFragmentManager();
FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();
fragmentTransaction.add(R.id.frame, myFragment);
fragmentTransaction.commit();
isTransactionPending=false;
}else {
/*
If any transaction is not done because the activity is in background. We set the
isTransactionPending variable to true so that we can pick this up when we come back to
foreground
*/
isTransactionPending=true;
}
}

本文 相当详细地解释了为什么会遇到这种异常，并比较了解决这种异常的各种方法。强烈推荐

小开

我也有同样的例外，我尝试了在这个堆栈溢出讨论中找到的许多代码片段，但是没有一个代码片段对我有用。

但我能够解决所有的问题，我将与你们分享解决方案:

  • 在第一部分中: 我试图在一个 Activity 上显示一个 DialogFragment，但它来自另一个 java 类。然后通过检查该实例的属性，我发现这是 Activity 的一个旧实例，而不是当前正在运行的 Activity。 [更准确地说，我使用的是 socket.io，但是我忘记了执行 socket.off (“ example”，example) ... ... 因此它附加到活动的一个旧实例。]

  • 在第二部分: 当我带着目的返回到 Activity 时，我试图在它中显示一个 DialogFragment，但是当我检查我的日志时，我发现当它试图显示活动片段时，它仍然不在 onStart 方法中，所以它崩溃了应用程序，因为它没有找到 Activity 类来显示片段。

一些提示: 检查一些属性，如果您没有使用您的活动的旧实例，您试图显示您的片段，或检查您的活动生命周期之前显示您的片段，并确保您在 onStart 或 onResume 之前显示它。

我希望这些解释对你有帮助。

小开

这解决了我的问题: 科特林代码:

val fragmentTransaction = activity.supportFragmentManager.beginTransaction()
fragmentTransaction.add(dialogFragment, tag)
fragmentTransaction.commitAllowingStateLoss()

commitAllowingStateLoss()和 commit()有什么不同？

根据文件:

类似于 commit()，但允许在保存活动状态后执行提交。 Https://developer.android.com/reference/android/app/fragmenttransaction#commitallowingstateloss

你可以显示片段对话框，也可以用这种方法加载片段。两种方法都适用。


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