Using ActionBar Up Navigation in master/detail fragments

Question

I have an app with master/detail layout (1 activity, 1 ListView fragment and 1 detail fragment). When the user clicks an item in the ListView, a fragment transaction instantiates a detail fragment on the right-pane that includes the information corresponding to that item. When the detail fragment is shown I hide the initial action bar buttons/items and show 3 new AB items (done/delete/cancel). The user can clean the right-pane and return to the initial UI state by either pressing the back button or by pressing one of the 3 AB items.

The issue I'm experiencing is that when the user selects the app's home icon (i.e. "up navigation") the activity gets re-loaded (i.e. the animation that indicates that the activity is starting can be seen as both the action bar and the UI is been redrawn). The issue only happens when the app home icon is pressed. If the user presses the back button or a cancel/done/delete action bar button, the fragment is simply remove from the right-pane and the UI returns to initial state without any "re-loading".

The XML layout for the activity is the following (inside LinearLayout; prettify is hiding that line):

<fragment class="*.*.*.ListFragment"
        android:id="@+id/titles" android:layout_weight="1"
        android:layout_width="0px"
        android:layout_height="match_parent" />

<FrameLayout android:id="@+id/details" android:layout_weight="2"
        android:layout_width="0px"
        android:layout_height="match_parent" />

The DetailsFragement has the actionBar.setDisplayHomeAsUpEnabled statement in its onCreate method:

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setHasOptionsMenu(true);


    ActionBar actionBar = getSherlockActivity().getSupportActionBar();
    actionBar.setDisplayHomeAsUpEnabled(true);

}

For both the ListView fragment and the Detail fragments the onCreateOptionsMenu() and onOptionsItemSelected() method are implemented within the fragments. Below the code for the Details fragment:

@Override
public void onCreateOptionsMenu(Menu menu, MenuInflater inflater) {
    inflater.inflate(R.menu.edit_menu, menu);
}

@Override
public boolean onOptionsItemSelected(MenuItem item) {

    // some variable statements...

    switch (item.getItemId()) {
        case android.R.id.home:
            //Toast.makeText(getSherlockActivity(), "Tapped home", Toast.LENGTH_SHORT).show();
            onHomeSelectedListener.onHomeSelected();
            return true;

        case R.id.menu_edit_item_done:
            editedTask.setTitle(editedTaskTitle);
            onTaskEditedListener.onTaskEdited(editedTask, UPDATE_TASK, true);
            return true;

        default:
            return super.onOptionsItemSelected(item);

    }
}

In the host activity I implement the onHomeSelectedListner to handle the app home icon press (i.e. "up navigation":

public void onHomeSelected(){

    FragmentManager manager = getSupportFragmentManager();
    FragmentTransaction ft = manager.beginTransaction();
    TaskFragment taskFragment = (TaskFragment)getSupportFragmentManager().findFragmentById(R.id.details);
    ft.remove(taskFragment);
    ft.commit();
    manager.popBackStack();

}

The activity's listener in charged of handling all other action bar buttons (i.e. done/delete/cancel) is onTaskEditedListener and, aside of other code that processes some data, it has the same fragment transactions shown above.

Update(1/24) Based on tyczj and straya feedback I placed log statements inside onCreate(), onResume(), onPause() of the activity to determine the differences between onHomeSelected and onTaskEdited listeners. I'm able to confirm that during the "up navigation" event (i.e. onHomeSelected) onPause(), onCreate() and onResume() are called. Whereas during the onTaskEdited call (i.e. back button or done/delete/cancel press) none of those events are called.

Update (1/25) Based on a suggestion by Mark Murphy, I commented out the onHomeSelected method call in the "case android.R.id.home" statement just to see what would the Activity do. The thinking was that the app would do nothing since the are no statements. Turns out that is not the case. Even without a call to the listener method (i.e. that removes the fragment), the activity is restarted and the detail fragment is removed from the fragment container.

Update (2/28) I temporarily workaround the fact that my main activity was getting restarted by disabling the window animations (as highlighted in my own answer). However, through further testing I uncovered a bug. Thanks to Wolfram Rittmeyer's sample code I was able to figure out the real reason(s) why my activity was restarting (in master/detail single layout) during up navigation: 1) Although I was using this "onHomeSelectedListener" to properly remove the fragment from the backstack, I still had some remnant code in the ListView fragment's onOptionsItemSelected that was creating a new intent to start the hosting activity. That's why pressing the app's home icon was re-starting the activity. 2) In my final implementation (shown in my own answer), I got rid of the onHomeSelectedListener in the activity and replace the startActivity intent (i.e. offending code) inside the ListView's onOptionsItemSelected to use the fragment removal + popBackStack code originally in the onHomeSelectedListener.

Answer 1

After much research and poking around, turns out that only reason why my activity was restarting during "up navigation" for master/detail configuration was because I left some code in the ListView Fragment's onOptionsItemSelected that was creating an intent to start the main activity in addition to my full fragment transaction code elsewhere. Below is the final implementation with which I got "up navigation" to work properly on both phone (multiple activities) and tablet (single activity/multi-pane) configurations. Thanks to Wolfram Rittmeyer for a couple of hints in his code (link in the comment section) that help me pinpoint my problem!

Main Activity: Hosts the fragments and performs some other app-specific operations

ListView Fragment: Handles "up navigation in table configuration

@Override
public boolean onOptionsItemSelected(MenuItem item) {
    switch (item.getItemId()) {
        case android.R.id.home:
            if(mDualPane){
                FragmentManager manager = getSherlockActivity().getSupportFragmentManager();
                FragmentTransaction ft = manager.beginTransaction();
                DetailFragment detailFragment = (DetailFragment)manager.findFragmentById(R.id.details);
                ft.remove(detailFragment);
                ft.commit();
                manager.popBackStack();
                getSherlockActivity().getSupportActionBar().setDisplayHomeAsUpEnabled(false);
                getSherlockActivity().getSupportActionBar().setHomeButtonEnabled(false);
            }
            return true;

        // Other case statements...

        default:
            return super.onOptionsItemSelected(item);
    }
}

Details Fragment: Handles up navigation in phone configuration

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setHasOptionsMenu(true);

    // Sets "up navigation" for both phone/tablet configurations
    ActionBar actionBar = getSherlockActivity().getSupportActionBar();
    actionBar.setDisplayHomeAsUpEnabled(true);
}

@Override
public boolean onOptionsItemSelected(MenuItem item) {

    switch (item.getItemId()) {
        case android.R.id.home:
            if(!mDualPane){
                Intent parentActivityIntent = new Intent(getSherlockActivity(), MainActivity.class);
                parentActivityIntent.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP | Intent.FLAG_ACTIVITY_NEW_TASK);
                startActivity(parentActivityIntent);
                getSherlockActivity().finish();
            }
            return true;

        // Other case statements...

        default:
            return super.onOptionsItemSelected(item);
    }

}

Answer 2

If you look at the Navigation Design Pattern you will see that you want to return to the starting activity when the home button is hit.

So say you have 2 Activities call them A1 and A2. Clicking on something in A1 takes you to A2. If the user hits the home button you should return them to A1 clearing the stack of everything up until that activity like this

Intent intent = new Intent(this, A1.class);  
intent.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
startActivity(intent);

this is what the flag Intent.FLAG_ACTIVITY_CLEAR_TOP does

If set, and the activity being launched is already running in the current task, then instead of launching a new instance of that activity, all of the other activities on top of it will be closed and this Intent will be delivered to the (now on top) old activity as a new Intent.

For example, consider a task consisting of the activities: A, B, C, D. If D calls startActivity() with an Intent that resolves to the component of activity B, then C and D will be finished and B receive the given Intent, resulting in the stack now being: A, B.`

The currently running instance of activity B in the above example will either receive the new intent you are starting here in its onNewIntent() method, or be itself finished and restarted with the new intent. If it has declared its launch mode to be "multiple" (the default) and you have not set FLAG_ACTIVITY_SINGLE_TOP in the same intent, then it will be finished and re-created; for all other launch modes or if FLAG_ACTIVITY_SINGLE_TOP is set then this Intent will be delivered to the current instance's onNewIntent().

This launch mode can also be used to good effect in conjunction with FLAG_ACTIVITY_NEW_TASK: if used to start the root activity of a task, it will bring any currently running instance of that task to the foreground, and then clear it to its root state. This is especially useful, for example, when launching an activity from the notification manager.