android - 为什么后台堆栈中的零 fragment

Question

我的简单布局只有一个 fragment 占位符:

<FrameLayout
   android:id="@+id/fragment_placeholder"
   android:layout_width="fill_parent"
   android:layout_height="fill_parent"
  />

我首先向这个占位符添加一个第一个 fragment :

fragmentTransaction.add(R.id.fragment_placeholder, firstFragment, "first"); //I did not put to backstack

我有一个第二个 fragment ，它替换了上面的 fragment 并将它放到后台堆栈:

FragmentManager fragMgr = getSupportFragmentManager();
FragmentTransaction fragTrans = fragMgr.beginTransaction();

//initialize an fragment instance
Fragment secondFragment = initSecondFragment(); 

//replace with the fragment 
fragTrans.replace(R.id.fragment_placeholder, secondFragment, "second");

//Add transaction to back stack
fragTrans.addToBackStack(null);

//commit the transaction
fragTrans.setTransition(FragmentTransaction.TRANSIT_FRAGMENT_FADE);
fragTrans.commit();  

//The following log returns me 0 when counting the number of fragments in back stack, why?  
Log.v("nr of fragment in back stack", fragMgr.getBackStackEntryCount()+"");

但我最终在返回堆栈中得到了 0 fragment ，为什么？？？

Answer 1

在 Log 之前尝试执行 executePendingTransactions() 以确保提交发生。 像这样:

fragMgr.executePendingTransactions();
Log.v("nr of fragment in back stack", fragMgr.getBackStackEntryCount()+"");

希望对你有帮助