为什么popbackstack调用片段的onCreateView? [英] Why does popbackstack call onCreateView of the fragment?

问题描述

试图弄清楚为什么我在弹出片段时会调用onCreateView.

使用以下代码:

fragmentManager.popBackStack("tag1", 1); 
ft = fragmentManager.beginTransaction(); 
ft.remove(fragmentManager.findFragmentByTag("tag1")); 
ft.commit();

Logcat:

FATAL EXCEPTION: main
java.lang.IndexOutOfBoundsException: Invalid index 79, size is 79
        at java.util.ArrayList.throwIndexOutOfBoundsException(ArrayList.java:255)
        at java.util.ArrayList.get(ArrayList.java:308)
        at edu.pacific.pocketrx.FlashCardFrag.onCreateView(FlashCardFrag.java:72)
        at android.support.v4.app.Fragment.performCreateView(Fragment.java:1500)
        at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:927)
        at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1104)
        at android.support.v4.app.BackStackRecord.popFromBackStack(BackStackRecord.java:764)
        at android.support.v4.app.FragmentManagerImpl.popBackStackState(FragmentManager.java:1562)
        at android.support.v4.app.FragmentManagerImpl$3.run(FragmentManager.java:495)
        at android.support.v4.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1467)
        at android.support.v4.app.FragmentManagerImpl$1.run(FragmentManager.java:440)
        at android.os.Handler.handleCallback(Handler.java:730)
        at android.os.Handler.dispatchMessage(Handler.java:92)
        at android.os.Looper.loop(Looper.java:137)
        at android.app.ActivityThread.main(ActivityThread.java:5103)
        at java.lang.reflect.Method.invokeNative(Native Method)
        at java.lang.reflect.Method.invoke(Method.java:525)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:737)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
        at dalvik.system.NativeStart.main(Native Method)

删除片段的代码:

fragmentManager.popBackStack("tag1", 1);
ft = fragmentManager.beginTransaction();
ft.remove(fragmentManager.findFragmentByTag("tag1"));
ft.commit();

解决方案

实际上，片段管理器不存储您的隐藏片段，它仅存储状态

BackStackState类实现了Parcelable

请参见

Logcat:

FATAL EXCEPTION: main
java.lang.IndexOutOfBoundsException: Invalid index 79, size is 79
        at java.util.ArrayList.throwIndexOutOfBoundsException(ArrayList.java:255)
        at java.util.ArrayList.get(ArrayList.java:308)
        at edu.pacific.pocketrx.FlashCardFrag.onCreateView(FlashCardFrag.java:72)
        at android.support.v4.app.Fragment.performCreateView(Fragment.java:1500)
        at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:927)
        at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1104)
        at android.support.v4.app.BackStackRecord.popFromBackStack(BackStackRecord.java:764)
        at android.support.v4.app.FragmentManagerImpl.popBackStackState(FragmentManager.java:1562)
        at android.support.v4.app.FragmentManagerImpl$3.run(FragmentManager.java:495)
        at android.support.v4.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1467)
        at android.support.v4.app.FragmentManagerImpl$1.run(FragmentManager.java:440)
        at android.os.Handler.handleCallback(Handler.java:730)
        at android.os.Handler.dispatchMessage(Handler.java:92)
        at android.os.Looper.loop(Looper.java:137)
        at android.app.ActivityThread.main(ActivityThread.java:5103)
        at java.lang.reflect.Method.invokeNative(Native Method)
        at java.lang.reflect.Method.invoke(Method.java:525)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:737)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
        at dalvik.system.NativeStart.main(Native Method)

Code to remove fragment:

fragmentManager.popBackStack("tag1", 1);
ft = fragmentManager.beginTransaction();
ft.remove(fragmentManager.findFragmentByTag("tag1"));
ft.commit();

解决方案

in fact fragment manager doesn't store your hidden fragment it stores only a state

class BackStackState implements Parcelable

see http://grepcode.com/file/repository.grepcode.com/java/ext/com.google.android/android/4.4_r1/android/support/v4/app/FragmentManager.java#FragmentManagerImpl.popBackStackState%28android.os.Handler%2Cjava.lang.String%2Cint%2Cint%29

and when you pop a fragment, fragment manager tries to recreate a previous view to display it.

see moveToState method

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