如何使用活动显示的片段转到上一个活动

Question

I have two activities, Activity A and Activity B. Now Activity A has 3 Fragments one of which launches activity B. When I press the action bar button it returns to activity A but shows the default Fragment . Am using navUtils.navigateupFromSameTask to go back to previous Activity .

How can I have the latest Fragment the user used show instead of the default one that shows up when user launches app the first time? For example when app launches it shows Fragment one. when user goes to Fragment 2 and launches activity B from it I want to go back to the previous activity showing fragment 2

@Override
public boolean onOptionsItemSelected(MenuItem item){
    switch(item.getItemId()){
    case android.R.id.home:
        NavUtils.navigateUpFromSameTask(this);
        return true;
    }
    return super.onOptionsItemSelected(item);
}

in the onCreate method I have

if (savedInstanceState == null) {
    fragmentManager = getFragmentManager();
    fragment = new RadioSound();
    selectItem(0);
}

then selectItem :

 private void selectItem(int position) {

    // update the main content by replacing fragments
 activeFrag = position;
 if(position == 0){
    fragmentManager.beginTransaction().replace(R.id.content_frame, fragment).commit();
 }
 else if(position == 1){
     if(conv == null)
     conv = new Conversations();
     fragmentManager.beginTransaction().replace(R.id.content_frame, conv).commit();
 } else{
     fragmentManager.beginTransaction().replace(R.id.content_frame, (new Preferences())).commit();
 }
    // update selected item and title, then close the drawer
    mDrawerList.setItemChecked(position, true);
    setTitle(fragments[position]);
    mDrawerLayout.closeDrawer(mDrawerList);
}

Answer 1

When you return from activity B to activity A you recreate your fragments, so it will always show your fragment1 instead of your desired fragment2.

Your problem is, that you trust on savedInstanceState to decide if your fragments should be recreated or not. However, onSaveInstanceState() is only called, when the activity gets destroyed, which will not instantly happen when you navigate to the next activity.

You should query the FragmentManager in your onCreate() method of activity A, if fragments are already added, otherwise you do your initial fragment creation. In order to do so, I would add an TAG to better find your fragments.

private static final String FRAGMENT_TAG_CONVERSATION = "frag_conv";
...
fragmentManager.beginTransaction().replace(R.id.content_frame, conv, FRAGMENT_TAG_CONVERSATION).commit();

You can then check, if you already added the fragment:

 if(fragmentManager.findFragmentByTag(FRAGMENT_TAG_CONVERSATION) == null))
     // only add it here