android - 为什么在 Activity 被销毁时调用 DialogFragment.onCreateView？

标签 android android-dialogfragment android-support-library

我正在使用 android 支持库 v4 修订版 11，我不时看到下面的堆栈跟踪；我怀疑这是由于最近的一次发射而发生的，因此我试图访问的模型是空的。无论如何，这个跟踪让我想知道为什么在 Activity 被销毁时调用 onCreateView，处理这种情况的最佳方法是什么？

java.lang.NullPointerException
    at com.example.dialogs.ExampleDialogFragment.onCreateView(ExampleDialogFragment.java:53)
    at android.support.v4.app.Fragment.performCreateView(Fragment.java:1460)
    at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:911)
    at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1088)
    at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1070)
    at android.support.v4.app.FragmentManagerImpl.dispatchReallyStop(FragmentManager.java:1888)
    at android.support.v4.app.FragmentActivity.onReallyStop(FragmentActivity.java:787)
    at android.support.v4.app.FragmentActivity.doReallyStop(FragmentActivity.java:764)
    at android.support.v4.app.FragmentActivity.onDestroy(FragmentActivity.java:322)
    at android.app.ActivityThread.performDestroyActivity(ActivityThread.java:3642)
    at android.app.ActivityThread.handleDestroyActivity(ActivityThread.java:3673)
    at android.app.ActivityThread.access$2900(ActivityThread.java:125)
    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2066)
    at android.os.Handler.dispatchMessage(Handler.java:99)
    at android.os.Looper.loop(Looper.java:123)
    at android.app.ActivityThread.main(ActivityThread.java:4627)
    at java.lang.reflect.Method.invokeNative(Native Method)
    at java.lang.reflect.Method.invoke(Method.java:521)
    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:858)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
    at dalvik.system.NativeStart.main(Native Method)

崩溃后，从 back-stack 恢复 Activity ，我确实检查模型在 onResume()、onStart() 和 Activity 中是否有效onCreate(Bundle savedInstanceState)。如果模型无效，我将使用 FLAG_ACTIVITY_NO_HISTORY 开始另一个 Activity ，调用 finish() 并 return; 例如

@Override
public void onResume() {        
    Model cm = Application.getModel();
    final boolean isModelAvailable = cm != null;
    if (!isModelAvailable) {
        Intent restartIntent = IntentUtil.intentForAction(Constants.INTENT_RESTART);
        restartIntent.setFlags(Intent.FLAG_ACTIVITY_NO_HISTORY);
        startActivity(restartIntent);
        finish();
        super.onResume();
        return;
    } else {

    }

INTENT_RESTART Activity 完成模型的重新初始化后，它会使用标志 FLAG_ACTIVITY_CLEAR_TOP 启动 Activity ，此 Activity 将事务提交到 fragment FirstFragment

使用 FragmentManager.enableDebugLogging(true); 查看日志。

05-13 13:24:53.051: V/FragmentManager(7468): Commit: BackStackEntry{40710fa0}
05-13 13:24:53.111: V/FragmentManager(7468): Commit: BackStackEntry{40771e78}
05-13 13:24:53.151: V/FragmentManager(7468): Run: BackStackEntry{40710fa0}
05-13 13:24:53.151: V/FragmentManager(7468): add: RetainFragment{4077d048 app_ImageCache}
05-13 13:24:53.151: V/FragmentManager(7468): Allocated fragment index RetainFragment{4077d048 #0 app_ImageCache}
05-13 13:24:53.151: V/FragmentManager(7468): moveto CREATED: RetainFragment{4077d048 #0 app_ImageCache}
05-13 13:24:53.151: V/FragmentManager(7468): moveto ACTIVITY_CREATED: RetainFragment{4077d048 #0 app_ImageCache}
05-13 13:24:53.151: V/FragmentManager(7468): Run: BackStackEntry{40771e78}
05-13 13:24:53.151: V/FragmentManager(7468): add: FirstFragment{4077dfa8 id=0x7f04000d}
05-13 13:24:53.151: V/FragmentManager(7468): Allocated fragment index FirstFragment{4077dfa8 #1 id=0x7f04000d}
05-13 13:24:53.151: V/FragmentManager(7468): moveto CREATED: FirstFragment{4077dfa8 #1 id=0x7f04000d}
05-13 13:24:53.151: V/FragmentManager(7468): moveto ACTIVITY_CREATED: FirstFragment{4077dfa8 #1 id=0x7f04000d}
05-13 13:24:53.791: V/FragmentManager(7468): moveto STARTED: RetainFragment{4077d048 #0 app_ImageCache}
05-13 13:24:53.791: V/FragmentManager(7468): moveto STARTED: FirstFragment{4077dfa8 #1 id=0x7f04000d}
05-13 13:24:53.811: V/FragmentManager(7468): moveto RESUMED: RetainFragment{4077d048 #0 app_ImageCache}
05-13 13:24:53.811: V/FragmentManager(7468): moveto RESUMED: FirstFragment{4077dfa8 #1 id=0x7f04000d}

05-13 13:25:58.414: V/FragmentManager(7468): Commit: BackStackEntry{40727530}
05-13 13:25:58.434: V/FragmentManager(7468): Run: BackStackEntry{4078fe00}
05-13 13:25:58.434: V/FragmentManager(7468): add: RetainFragment{4076f1b0 app_ImageCache}
05-13 13:25:58.434: V/FragmentManager(7468): Allocated fragment index RetainFragment{4076f1b0 #0 app_ImageCache}
05-13 13:25:58.434: V/FragmentManager(7468): moveto CREATED: RetainFragment{4076f1b0 #0 app_ImageCache}
05-13 13:25:58.434: V/FragmentManager(7468): moveto ACTIVITY_CREATED: RetainFragment{4076f1b0 #0 app_ImageCache}
05-13 13:25:58.434: V/FragmentManager(7468): Run: BackStackEntry{40727530}
05-13 13:25:58.434: V/FragmentManager(7468): add: SecondFragment{40713c28 id=0x7f04000d}
05-13 13:25:58.434: V/FragmentManager(7468): Allocated fragment index SecondFragment{40713c28 #1 id=0x7f04000d}
05-13 13:25:58.434: V/FragmentManager(7468): moveto CREATED: SecondFragment{40713c28 #1 id=0x7f04000d}
05-13 13:25:58.434: V/FragmentManager(7468): moveto ACTIVITY_CREATED: SecondFragment{40713c28 #1 id=0x7f04000d}
05-13 13:25:58.545: V/FragmentManager(7468): moveto STARTED: RetainFragment{4076f1b0 #0 app_ImageCache}
05-13 13:25:58.545: V/FragmentManager(7468): moveto STARTED: SecondFragment{40713c28 #1 id=0x7f04000d}
05-13 13:25:58.565: V/FragmentManager(7468): moveto RESUMED: RetainFragment{4076f1b0 #0 app_ImageCache}
05-13 13:25:58.565: V/FragmentManager(7468): moveto RESUMED: SecondFragment{40713c28 #1 id=0x7f04000d}

05-13 13:26:02.338: V/FragmentManager(7468): Saved state of RetainFragment{4077d048 #0 app_ImageCache}: null
05-13 13:26:02.338: V/FragmentManager(7468): Saved state of FirstFragment{4077dfa8 #1 id=0x7f04000d}: Bundle[{android:view_state=android.util.SparseArray@40b15b60}]
05-13 13:26:02.338: V/FragmentManager(7468): saveAllState: adding fragment #0: RetainFragment{4077d048 #0 app_ImageCache}
05-13 13:26:02.338: V/FragmentManager(7468): saveAllState: adding fragment #1: FirstFragment{4077dfa8 #1 id=0x7f04000d}
05-13 13:26:02.348: V/FragmentManager(7468): movefrom STARTED: RetainFragment{4077d048 #0 app_ImageCache}
05-13 13:26:02.348: V/FragmentManager(7468): movefrom STARTED: FirstFragment{4077dfa8 #1 id=0x7f04000d}
05-13 13:26:02.358: V/FragmentManager(7468): movefrom STOPPED: RetainFragment{4077d048 #0 app_ImageCache}
05-13 13:26:02.358: V/FragmentManager(7468): movefrom STOPPED: FirstFragment{4077dfa8 #1 id=0x7f04000d}
05-13 13:27:15.219: V/FragmentManager(7468): movefrom RESUMED: RetainFragment{4076f1b0 #0 app_ImageCache}
05-13 13:27:15.219: V/FragmentManager(7468): movefrom RESUMED: SecondFragment{40713c28 #1 id=0x7f04000d}

05-13 13:27:15.239: V/FragmentManager(7468): Commit: BackStackEntry{40a8a6d0}
05-13 13:27:15.259: V/FragmentManager(7468): Commit: BackStackEntry{40a90190}

05-13 13:27:15.279: V/FragmentManager(7468): Run: BackStackEntry{40a8a6d0}
05-13 13:27:15.279: V/FragmentManager(7468): add: RetainFragment{40a7fdf0 app_ImageCache}
05-13 13:27:15.279: V/FragmentManager(7468): Allocated fragment index RetainFragment{40a7fdf0 #0 app_ImageCache}
05-13 13:27:15.279: V/FragmentManager(7468): moveto CREATED: RetainFragment{40a7fdf0 #0 app_ImageCache}
05-13 13:27:15.279: V/FragmentManager(7468): moveto ACTIVITY_CREATED: RetainFragment{40a7fdf0 #0 app_ImageCache}
05-13 13:27:15.279: V/FragmentManager(7468): Run: BackStackEntry{40a90190}
05-13 13:27:15.279: V/FragmentManager(7468): add: ThirdFragment{406c2308 id=0x7f04000d}
05-13 13:27:15.279: V/FragmentManager(7468): Allocated fragment index ThirdFragment{406c2308 #1 id=0x7f04000d}
05-13 13:27:15.289: V/FragmentManager(7468): moveto CREATED: ThirdFragment{406c2308 #1 id=0x7f04000d}
05-13 13:27:15.289: V/FragmentManager(7468): moveto ACTIVITY_CREATED: ThirdFragment{406c2308 #1 id=0x7f04000d}
05-13 13:27:15.410: V/FragmentManager(7468): moveto STARTED: RetainFragment{40a7fdf0 #0 app_ImageCache}
05-13 13:27:15.410: V/FragmentManager(7468): moveto STARTED: ThirdFragment{406c2308 #1 id=0x7f04000d}
05-13 13:27:15.430: V/FragmentManager(7468): moveto RESUMED: RetainFragment{40a7fdf0 #0 app_ImageCache}
05-13 13:27:15.430: V/FragmentManager(7468): moveto RESUMED: ThirdFragment{406c2308 #1 id=0x7f04000d}
05-13 13:27:15.810: V/FragmentManager(7468): Saved state of RetainFragment{4076f1b0 #0 app_ImageCache}: null
05-13 13:27:15.810: V/FragmentManager(7468): Saved state of SecondFragment{40713c28 #1 id=0x7f04000d}: Bundle[{android:view_state=android.util.SparseArray@40aa62c0}]
05-13 13:27:15.810: V/FragmentManager(7468): saveAllState: adding fragment #0: RetainFragment{4076f1b0 #0 app_ImageCache}
05-13 13:27:15.810: V/FragmentManager(7468): saveAllState: adding fragment #1: SecondFragment{40713c28 #1 id=0x7f04000d}
05-13 13:27:15.810: V/FragmentManager(7468): movefrom STARTED: RetainFragment{4076f1b0 #0 app_ImageCache}
05-13 13:27:15.810: V/FragmentManager(7468): movefrom STARTED: SecondFragment{40713c28 #1 id=0x7f04000d}
05-13 13:27:15.820: V/FragmentManager(7468): movefrom STOPPED: RetainFragment{4076f1b0 #0 app_ImageCache}
05-13 13:27:15.820: V/FragmentManager(7468): movefrom STOPPED: SecondFragment{40713c28 #1 id=0x7f04000d}


// Here I'm waiting for a while to make sure Android has enough time to do anything it wants, then I press a button gorse-closing the app  
05-13 13:27:59.783: D/AndroidRuntime(7468): Shutting down VM


05-13 13:28:14.928: V/FragmentManager(7523): Instantiated fragment RetainFragment{406cde80 #0 app_ImageCache}
05-13 13:28:14.938: V/FragmentManager(7523): restoreAllState: active #0: RetainFragment{406cde80 #0 app_ImageCache}
05-13 13:28:14.938: V/FragmentManager(7523): Instantiated fragment FirstFragment{406d8410 #1 id=0x7f04000d}
05-13 13:28:14.938: V/FragmentManager(7523): restoreAllState: active #1: FirstFragment{406d8410 #1 id=0x7f04000d}
05-13 13:28:14.938: V/FragmentManager(7523): restoreAllState: added #0: RetainFragment{406cde80 #0 app_ImageCache}
05-13 13:28:14.938: V/FragmentManager(7523): restoreAllState: added #1: FirstFragment{406d8410 #1 id=0x7f04000d}
05-13 13:28:14.938: V/FragmentManager(7523): moveto CREATED: RetainFragment{406cde80 #0 app_ImageCache}
05-13 13:28:14.938: V/FragmentManager(7523): moveto CREATED: FirstFragment{406d8410 #1 id=0x7f04000d}

05-13 13:28:15.128: V/msm8660.gralloc(7523): PmemUserspaceAllocator::PmemUserspaceAllocator(PmemUserspaceAllocator::Deps&, PmemUserspaceAllocator::Deps::Allocator&, const char*) begin
05-13 13:28:15.138: V/msm8660.gralloc(7523): PmemUserspaceAllocator::PmemUserspaceAllocator(PmemUserspaceAllocator::Deps&, PmemUserspaceAllocator::Deps::Allocator&, const char*) end
05-13 13:28:15.138: V/msm8660.gralloc(7523): PmemKernelAllocator::PmemKernelAllocator(PmemKernelAllocator::Deps&) begin
05-13 13:28:15.138: V/msm8660.gralloc(7523): PmemKernelAllocator::PmemKernelAllocator(PmemKernelAllocator::Deps&) end

05-13 13:28:15.408: V/FragmentManager(7523): moveto ACTIVITY_CREATED: RetainFragment{406cde80 #0 app_ImageCache}
05-13 13:28:15.408: V/FragmentManager(7523): moveto ACTIVITY_CREATED: FirstFragment{406d8410 #1 id=0x7f04000d}

java.lang.RuntimeException: Unable to destroy activity {com.myapp/com.myapp.activity.FirstFragment}: java.lang.NullPointerException

05-13 13:35:41.824: E/AndroidRuntime(7691):     at android.app.ActivityThread.performDestroyActivity(ActivityThread.java:3272)
05-13 13:35:41.824: E/AndroidRuntime(7691):     at android.app.ActivityThread.handleDestroyActivity(ActivityThread.java:3299)
05-13 13:35:41.824: E/AndroidRuntime(7691):     at android.app.ActivityThread.access$2100(ActivityThread.java:134)
05-13 13:35:41.824: E/AndroidRuntime(7691):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1143)
05-13 13:35:41.824: E/AndroidRuntime(7691):     at android.os.Handler.dispatchMessage(Handler.java:99)
05-13 13:35:41.824: E/AndroidRuntime(7691):     at android.os.Looper.loop(Looper.java:152)
05-13 13:35:41.824: E/AndroidRuntime(7691):     at android.app.ActivityThread.main(ActivityThread.java:4606)
05-13 13:35:41.824: E/AndroidRuntime(7691):     at java.lang.reflect.Method.invokeNative(Native Method)
05-13 13:35:41.824: E/AndroidRuntime(7691):     at java.lang.reflect.Method.invoke(Method.java:491)
05-13 13:35:41.824: E/AndroidRuntime(7691):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:841)
05-13 13:35:41.824: E/AndroidRuntime(7691):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:599)
05-13 13:35:41.824: E/AndroidRuntime(7691):     at dalvik.system.NativeStart.main(Native Method)

// see the original question log, it is quite the same
05-13 13:35:41.824: E/AndroidRuntime(7691): Caused by: java.lang.NullPointerException
05-13 13:35:41.824: E/AndroidRuntime(7691):     at com.myapp/com.myapp.activity.FirstFragment.onCreateView(FirstFragment.java:41)
05-13 13:35:41.824: E/AndroidRuntime(7691):     at android.support.v4.app.Fragment.performCreateView(Fragment.java:1460)
05-13 13:35:41.824: E/AndroidRuntime(7691):     at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:911)
05-13 13:35:41.824: E/AndroidRuntime(7691):     at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1088)
05-13 13:35:41.824: E/AndroidRuntime(7691):     at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1070)
05-13 13:35:41.824: E/AndroidRuntime(7691):     at android.support.v4.app.FragmentManagerImpl.dispatchReallyStop(FragmentManager.java:1888)
05-13 13:35:41.824: E/AndroidRuntime(7691):     at android.support.v4.app.FragmentActivity.onReallyStop(FragmentActivity.java:787)
05-13 13:35:41.824: E/AndroidRuntime(7691):     at android.support.v4.app.FragmentActivity.doReallyStop(FragmentActivity.java:764)
05-13 13:35:41.824: E/AndroidRuntime(7691):     at android.support.v4.app.FragmentActivity.onDestroy(FragmentActivity.java:322)
05-13 13:35:41.824: E/AndroidRuntime(7691):     at com.myapp.activity.FragmentsContainerActivity.onDestroy(FragmentsContainerActivity.java:806)
05-13 13:35:41.824: E/AndroidRuntime(7691):     at android.app.Activity.performDestroy(Activity.java:4662)
05-13 13:35:41.824: E/AndroidRuntime(7691):     at android.app.Instrumentation.callActivityOnDestroy(Instrumentation.java:1113)
05-13 13:35:41.824: E/AndroidRuntime(7691):     at android.app.ActivityThread.performDestroyActivity(ActivityThread.java:3255)
05-13 13:35:41.824: E/AndroidRuntime(7691):     ... 11 more

FragmentsContainerActivity 的第 806 行是 super.onDestroy();:

@Override
public void onDestroy() {
    try {
        unregister(receiver);
    } catch (Exception e) {
    }
    super.onDestroy();

最佳答案

按照 code sample here 中的指导引用 onResume 方法您应该:

Always call the superclass method first

意思是你应该把你的 super.onResume(); 放在开头。 这一定是问题所在。

在您当前运行的代码中，您混淆了被告知停止(即 finish)然后被告知 resume 的 FragmentActivity。 Activity 生命周期中不“合法”的生命周期。 fragment 直接受此影响，因为它们的生命周期是从 Activity 生命周期调用的，如果 Activity 从 finishing -> resume 进行，则肯定意味着 fragment 从 finishing/销毁 -> 恢复(通过 onCreateView)。

关于android - 为什么在 Activity 被销毁时调用 DialogFragment.onCreateView？，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/14866854/

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