为什么FragmentManager的BackStackEntry是0，即使我执行addToBackStack(null)

Question

private BaseFragment fragment;
private FragmentManager fragmentManager;
private FragmentManager fragmentManager1;
private FragmentTransaction aFragmentTransaction;

这是我的OnCreate((方法中的代码：

fragmentManager = getSupportFragmentManager();
fragmentManager.beginTransaction().replace(R.id.frame_container, 
fragment).commit();
fragmentTitle = getResources().getString(fragment.getFragmentTitle());
setTitle(fragmentTitle);

....更多代码...

aFragmentTransaction = fragmentManager.beginTransaction();
aFragmentTransaction.replace(R.id.frame_container, fragment);
aFragmentTransaction.addToBackStack(null);
aFragmentTransaction.commit();
setTitle(getResources().getString(fragment.getFragmentTitle()));

这是方法OnBackPressed((中同一活动中的代码：

@Override
public void onBackPressed(){
fragmentManager1 = getSupportFragmentManager();
if (fragmentManager1.getBackStackEntryCount() > 0) {
fragmentManager1.popBackStack();
} else {
super.onBackPressed();
}

两者位于同一活动中。 当我调试时，BackStack 有 0 个元素。

编辑：执行aFragmentTransaction.addToBackStack(null(后，BackStack仍然保持null

Answer 1

因为你替换了它而不是添加它。 像这样做：

aFragmentTransaction.add(R.id.frame_container, fragment);