即使添加addToBackStack和executePendingTransactions()，getBackStackEntryCount()始终返回0.

问题描述

我有两个活动A和B.活动A有一个mapFragment，我正在将它添加到Backstack中.当我从B回到Actvity A时，我希望片段以与离开时相同的状态显示.但是getFragmentManager().getBackStackEntryCount()返回我0.这是我的代码:

I have two activities A and B. Activity A has a mapFragment and I am adding it to backstack. When I come back from to Actvity A from B, I want the fragment to show up in same state as I left it. But getFragmentManager().getBackStackEntryCount() is returning me 0. Here is my code:

MapFragment mMapFragment = MapFragment.newInstance();
    FragmentTransaction fragmentTransaction = getFragmentManager().beginTransaction();
    mMapFragment.getMapAsync(this);
    fragmentTransaction.replace(R.id.container, mMapFragment);
    fragmentTransaction.addToBackStack(null);
    fragmentTransaction.commit();
    getFragmentManager().executePendingTransactions();

从活动B回来时，我想知道getBackStackEntryCount()的数量:

When coming back from activity B, I have this to know number of getBackStackEntryCount():

System.out.println("Number of entries in backstack "+ getFragmentManager().getBackStackEntryCount());

显示0.

谢谢.

推荐答案

我遇到了类似的问题，在我的情况下， getFragmentManager().getBackStackEntryCount()始终返回零.

I had a similar problem, in my case getFragmentManager().getBackStackEntryCount() was always returning zero.

我的问题是我正在使用支持片段:

My problem was I've using support fragments:

Fragment fragment = new MyFragment();
// note getSupportFragmentManager() instead getFragmentManager()
FragmentManager fragmentManager = getSupportFragmentManager();
fragmentManager.beginTransaction()
.replace(R.id.frame, fragment)
.addToBackStack(null)
.commit();

fragmentManager.executePendingTransactions();

，并且我正在检查 getFragmentManager() backStackEntryCount ，它始终返回零(它正在使用另一个片段管理器):

and I've checking getFragmentManager() backStackEntryCount, which always returns zero (it's using another fragment manager):

@Override
public void onBackPressed() {
    if (getFragmentManager().getBackStackEntryCount() > 0 ) {
        getFragmentManager().popBackStack();
    }
}

而不是 getSupportFragmentManager ，后者将返回正确的数字:

instead of getSupportFragmentManager, which returns the correct number:

@Override
public void onBackPressed() {
    if (getSupportFragmentManager().getBackStackEntryCount() > 0 ) {
        getSupportFragmentManager().popBackStack();
    }
}

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