带有ChildFragmentManager的FragmentStatePagerAdapter - FragmentManagerImpl.getFragment导致NullPointerException

Question

编辑2

我现在设法通过使用https://code.google.com/p/android/issues/detail?id=42601#c10中的技巧摆脱错误,这就是为什么我的上一次编辑被置于顶部的原因我的问题

但这导致了下一个错误:

java.lang.NullPointerException
at android.support.v4.app.FragmentManagerImpl.getFragment(FragmentManager.java:569)
at android.support.v4.app.FragmentStatePagerAdapter.restoreState(FragmentStatePagerAdapter.java:211)
at android.support.v4.view.ViewPager.onRestoreInstanceState(ViewPager.java:1281)
at android.view.View.dispatchRestoreInstanceState(View.java:12043)
at android.view.ViewGroup.dispatchRestoreInstanceState(ViewGroup.java:2688)
at android.view.ViewGroup.dispatchRestoreInstanceState(ViewGroup.java:2694)
at android.view.ViewGroup.dispatchRestoreInstanceState(ViewGroup.java:2694)
at android.view.View.restoreHierarchyState(View.java:12021)
at android.support.v4.app.Fragment.restoreViewState(Fragment.java:425)
at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:949)
at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1104)
at android.support.v4.app.BackStackRecord.run(BackStackRecord.java:682)
at android.support.v4.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1460)
at android.support.v4.app.FragmentManagerImpl$1.run(FragmentManager.java:440)
at android.os.Handler.handleCallback(Handler.java:615)
at android.os.Handler.dispatchMessage(Handler.java:92)
at android.os.Looper.loop(Looper.java:137)
at android.app.ActivityThread.main(ActivityThread.java:4800)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:511)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:798)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:565)
at dalvik.system.NativeStart.main(Native Method)

现在我不知道从哪里继续......

编辑0 - 第一个问题

我得到以下异常:

java.lang.IllegalStateException: No activity
at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1091)
at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1086)
at android.support.v4.app.FragmentManagerImpl.dispatchActivityCreated(FragmentManager.java:1877)
at android.support.v4.app.Fragment.performActivityCreated(Fragment.java:1492)
at android.support.v4.app._HoloFragment.performActivityCreated(_HoloFragment.java:251)
at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:947)
at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1104)
at android.support.v4.app.BackStackRecord.run(BackStackRecord.java:682)
at android.support.v4.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1460)
at android.support.v4.app.FragmentManagerImpl$1.run(FragmentManager.java:440)
at android.os.Handler.handleCallback(Handler.java:615)
at android.os.Handler.dispatchMessage(Handler.java:92)
at android.os.Looper.loop(Looper.java:137)
at android.app.ActivityThread.main(ActivityThread.java:4800)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:511)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:798)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:565)
at dalvik.system.NativeStart.main(Native Method)

我不知道从哪里开始.我正在使用最新的支持库(v4,rev18).

直到我添加了一个一切正常Fragment,其保持ViewPager与组合FragmentStatePagerAdapter.

我到处都在使用支持库,我尝试了https://code.google.com/p/android/issues/detail?id=42601的解决方案......

但还没有任何效果......

我不知道从哪里开始,有人有提示吗？

编辑1:背景和代码

1)在我的MainActivity中,我使用以下内容:

第三页有viewpager ...

public void setPage(int pos, boolean addToBackStack)
 {
    Fragment nextFragment = null;
    FragmentTransaction transaction = null;

    switch (pos)
    {
        case 0:
            if (mFragmentAllRoutines == null)
                mFragmentAllRoutines = new RoutinesListFragment();
            if (!mFragmentAllRoutines.isVisible())
                nextFragment = mFragmentAllRoutines;
            break;
        case 1:
            if (mFragmentRoutine == null)
                mFragmentRoutine = new RoutineFragment();
            if (!mFragmentRoutine.isVisible())
                nextFragment = mFragmentRoutine;
            break;
        case 2:
            if (mFragmentDay == null)
                mFragmentDay = new RoutineDayFragment();
            if (!mFragmentDay.isVisible())
                nextFragment = mFragmentDay;
            break;
        default:
            break;
    }

    if (nextFragment != null)
    {
        // Fragment prevFragment = getSupportFragmentManager().findFragmentById(R.id.fragment);
        transaction = getSupportFragmentManager().beginTransaction();
        // if (prevFragment != null)
        //    transaction.detach(prevFragment);
        transaction.replace(R.id.fragment, nextFragment, nextFragment.getClass().getName());
        // transaction.attach(nextFragment);
        if (addToBackStack)
            transaction.addToBackStack(null);
        transaction.commit();
    }
}

2)第三个片段:

它是一个带有ViewPager和FragmentStatePagerAdapter的简单片段.FragmentStatePagerAdapter获取getChildFragmentManager()为FragmentManager.在某个地方似乎存在问题.

Answer 1

我需要看到更多的代码才能知道在哪里应用这个...但是我遇到了类似的情况......我ChildFragmentManager以同样的方式解决了问题,并且NullPointerException像你一样得到了相同的结果.

我确实设法解决了......我会尝试描述我的解决方案,就像你提供的代码一样,我不确定在哪里应用"修复"...这真的是一个修复...它不是一个优雅的方式解决这个问题!然而它确实对我有所帮助,一旦我离开视图寻呼机,我就不需要恢复状态,因此对我来说没有任何不利因素.

我有多个片段,实现代码的静态位和onDetach(在https://code.google.com/p/android/issues/detail?id=42601#c10上),每个片段都有一个寻呼机和onCreateView我附加了一个扩展FragmentStatePagerAdapter的适配器.

在那些适配器上,我已经覆盖了restoreState方法,什么都不做

    @Override
public void restoreState(Parcelable arg0, ClassLoader arg1) {
    //do nothing here! no call to super.restoreState(arg0, arg1);
}

再次,这不是最好的方式......但它确实解决了我的问题.

祝你好运!

Answer 2

我偶然发现了同样的问题.

java.lang.NullPointerException: Attempt to invoke virtual method 'int java.util.ArrayList.size()' on a null object reference
     at android.support.v4.app.FragmentManagerImpl.getFragment(FragmentManager.java:873)
     at android.support.v4.app.FragmentStatePagerAdapter.restoreState(FragmentStatePagerAdapter.java:215)

Marc的解决方案有效,但就我而言,它会在Fragment with FragmentStatePagerAdapter上造成滞后.所以我覆盖了restoreState,称为super,将它包装在try/catch中,它没有滞后.

@Override
public void restoreState(Parcelable state, ClassLoader loader) {
    try{
        super.restoreState(state, loader);
    }catch (NullPointerException e){
        // null caught
    }
}

更新:

从那时起,我一直在使用这种解决方案.所以使用起来是安全的.