Android-修改后的目标片段在对话框片段中的更改

Question

我有一个片段，它添加了一个选项到选项菜单。当单击此选项时，将打开一个对话框片段。对话框将原始片段设置为其目标片段。如果在对话片段打开时没有发生方向变化，则目标片段与预期的一样，但是在方向变化之后，目标片段被设置为对话片段本身，而不是先前设置的片段。结果，当试图将目标片段强制转换为被设置为目标片段的片段时，我得到了一个classCastException。我需要在对话框中获取目标片段，因为它实现了一个回调（OnStartOrRestartLoader）。我已经试图解决这个问题一个多星期了，如果有人能给我指明正确的方向，我将非常感谢。因为这是我在这里的第一个问题，如果我排除了一些必要的信息，或者如果这不是一个合适的问题，我道歉。

FragmentManager fm = getChildFragmentManager();
SearchDialogFragment dialog = new SearchDialogFragment();
dialog.show(fm, "searchDialog");
dialog.setTargetFragment(this, DIALOGFRAGMENT);

OnStartOrRestartLoader callback = (OnStartOrRestartLoader) getTargetFragment();

08-25 12:15:55.087: E/AndroidRuntime(10057): FATAL EXCEPTION: main
08-25 12:15:55.087: E/AndroidRuntime(10057): Process: com.example, PID: 10057
08-25 12:15:55.087: E/AndroidRuntime(10057): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example/com.example.MainActivity}: java.lang.ClassCastException: com.example.SearchDialogFragment cannot be cast to com.example.OnStartOrRestartLoader
08-25 12:15:55.087: E/AndroidRuntime(10057):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2224)
08-25 12:15:55.087: E/AndroidRuntime(10057):    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2273)
08-25 12:15:55.087: E/AndroidRuntime(10057):    at android.app.ActivityThread.handleRelaunchActivity(ActivityThread.java:3759)
08-25 12:15:55.087: E/AndroidRuntime(10057):    at android.app.ActivityThread.access$900(ActivityThread.java:141)
08-25 12:15:55.087: E/AndroidRuntime(10057):    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1208)
08-25 12:15:55.087: E/AndroidRuntime(10057):    at android.os.Handler.dispatchMessage(Handler.java:102)
08-25 12:15:55.087: E/AndroidRuntime(10057):    at android.os.Looper.loop(Looper.java:136)
08-25 12:15:55.087: E/AndroidRuntime(10057):    at android.app.ActivityThread.main(ActivityThread.java:5052)
08-25 12:15:55.087: E/AndroidRuntime(10057):    at java.lang.reflect.Method.invokeNative(Native Method)
08-25 12:15:55.087: E/AndroidRuntime(10057):    at java.lang.reflect.Method.invoke(Method.java:515)
08-25 12:15:55.087: E/AndroidRuntime(10057):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:785)
08-25 12:15:55.087: E/AndroidRuntime(10057):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:601)
08-25 12:15:55.087: E/AndroidRuntime(10057):    at de.robv.android.xposed.XposedBridge.main(XposedBridge.java:132)
08-25 12:15:55.087: E/AndroidRuntime(10057):    at dalvik.system.NativeStart.main(Native Method)
08-25 12:15:55.087: E/AndroidRuntime(10057): Caused by: java.lang.ClassCastException: com.example.SearchDialogFragment cannot be cast to com.example.OnStartOrRestartLoader
08-25 12:15:55.087: E/AndroidRuntime(10057):    at com.example.SearchDialogFragment.onCreateDialog(SearchDialogFragment.java:59)
08-25 12:15:55.087: E/AndroidRuntime(10057):    at android.support.v4.app.DialogFragment.getLayoutInflater(DialogFragment.java:307)
08-25 12:15:55.087: E/AndroidRuntime(10057):    at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:942)
08-25 12:15:55.087: E/AndroidRuntime(10057):    at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1121)
08-25 12:15:55.087: E/AndroidRuntime(10057):    at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1103)
08-25 12:15:55.087: E/AndroidRuntime(10057):    at android.support.v4.app.FragmentManagerImpl.dispatchActivityCreated(FragmentManager.java:1901)
08-25 12:15:55.087: E/AndroidRuntime(10057):    at android.support.v4.app.Fragment.performActivityCreated(Fragment.java:1518)
08-25 12:15:55.087: E/AndroidRuntime(10057):    at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:962)
08-25 12:15:55.087: E/AndroidRuntime(10057):    at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1121)
08-25 12:15:55.087: E/AndroidRuntime(10057):    at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1103)
08-25 12:15:55.087: E/AndroidRuntime(10057):    at android.support.v4.app.FragmentManagerImpl.dispatchActivityCreated(FragmentManager.java:1901)
08-25 12:15:55.087: E/AndroidRuntime(10057):    at android.support.v4.app.FragmentActivity.onStart(FragmentActivity.java:567)
08-25 12:15:55.087: E/AndroidRuntime(10057):    at android.app.Instrumentation.callActivityOnStart(Instrumentation.java:1171)
08-25 12:15:55.087: E/AndroidRuntime(10057):    at android.app.Activity.performStart(Activity.java:5322)
08-25 12:15:55.087: E/AndroidRuntime(10057):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2187)
08-25 12:15:55.087: E/AndroidRuntime(10057):    ... 13 more

Answer 1

SetTargetFragment不应用于在父/子片段之间建立关系。它只应用于链接兄弟片段（即存在于同一fragmentManager中的片段）。

它不能在父/子片段之间工作的原因是片段的目标被保存并还原为它自己的fragmentManager中的索引。因此，在框架恢复一个活动之前，一切都将是健康的，例如，方向变化。此时，fragmentManager将在其内部查找目标片段，而不是父级fragmentManager。