Handling ActionBar title with the fragment back stack?

Question

I have an Activity where I load in a ListFragment and, upon clicking, it drills down a level and a new type of ListFragment is shown,

Answer 1

Warpzit is right. This also solves title problem when orientation of device is changed. Also if you use support v7 for action bar, you can get action bar from fragment like this :

@Override
public void onResume() {
    super.onResume();
    ((ActionBarActivity)getActivity()).getSupportActionBar().setTitle("Home");
}

Answer 2

As described here my solution is adding this code to MainActivity onCreate method(): and changing actionbar title

FragmentManager fragmentManager=getSupportFragmentManager();
fragmentManager.addOnBackStackChangedListener(new FragmentManager.OnBackStackChangedListener() {
    @Override
    public void onBackStackChanged() {
        Fragment currentFragment = fragmentManager.findFragmentById(R.id.My_Container_1_ID);
        currentFragment.onResume();
    }
});

and changing actionbar title in fragment's onResume() method

@Override
public void onResume() {
    super.onResume();
    AppCompatActivity activity = (AppCompatActivity) getActivity();
    ActionBar actionBar = activity.getSupportActionBar();
    if(actionBar!=null) {
        actionBar.setTitle("Fragment Title");
        actionBar.setSubtitle("Subtitle");
    }

}

Answer 3

It is best to let the OS do as much of the work as possible. Assuming each fragment is properly named using .addToBackStack("title") then you can override onBackPressed something like this to achieve desired behavior:

// this example uses the AppCompat support library
// and works for dynamic fragment titles
@Override
public void onBackPressed() {
    FragmentManager fragmentManager = getSupportFragmentManager();
    int count = fragmentManager.getBackStackEntryCount();
    if (count <= 1) {
        finish();
    }
    else {
        String title = fragmentManager.getBackStackEntryAt(count-2).getName();
        if (count == 2) {
            // here I am using a NavigationDrawer and open it when transitioning to the initial fragment
            // a second back-press will result in finish() being called above.
            mDrawerLayout.openDrawer(mNavigationDrawerFragment.getView());
        }
        super.onBackPressed();
        Log.v(TAG, "onBackPressed - title="+title);
        getSupportActionBar().setTitle(title);
    }
}

Answer 4

Use Fragments method:

@Override
public void onCreateOptionsMenu(Menu menu, MenuInflater inflater)

It is called on every Fragment appearance, but onResume is not.

Answer 5

In every fragment and every activity I change the title like this. This way the active title will always be correct:

@Override
public void onResume() {
    super.onResume();
    // Set title
    getActivity().getActionBar()
        .setTitle(R.string.thetitle);
}

There is some cases where onResume isn't called inside fragments. In some of these cases we can use:

public void setUserVisibleHint(boolean isVisibleToUser) {
    super.setUserVisibleHint(isVisibleToUser);
    if(isVisibleToUser) {
        // Set title
        getActivity().getActionBar()
            .setTitle(R.string.thetitle);
    }
}

Answer 6

The best approach is to make use of the android provided Interface OnBackStackChangedListener method onBackStackChanged().

Lets say we have a navigation drawer with 4 options to which the user can navigate to. In that case we will have 4 fragments. Lets see the code first and then I will explain the working.

    private int mPreviousBackStackCount = 0;
    private String[] title_name = {"Frag1","Frag2","Frag3","Frag4"};
    Stack<String> mFragPositionTitleDisplayed;

    public class MainActivity extends ActionBarActivity implements FragmentManager.OnBackStackChangedListener
    @Override
    protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    ....
    ....
    ....
    getSupportFragmentManager().addOnBackStackChangedListener(this);
    mFragPositionTitleDisplayed = new Stack<>();
}

public void displayFragment() {
    Fragment fragment = null;
    String title = getResources().getString(R.string.app_name);
    switch (position) {
        case 0:
            fragment = new Fragment1();
            title = title_name[position];
            break;
        case 1:
            fragment = new Fragment2();
            title = title_name[position];
            break;
        case 2:
            fragment = new Fragment3();
            title = title_name[position];
            break;
        case 3:
            fragment = new Fragment4();
            title = title_name[position];
            break;
        default:
            break;
    }
    if (fragment != null) {
        FragmentManager fragmentManager = getSupportFragmentManager();
        fragmentManager.beginTransaction()
                .replace(R.id.container_body, fragment)
                .addToBackStack(null)
                .commit();
        getSupportActionBar().setTitle(title);
    }
}

@Override
public void onBackStackChanged() {
    int backStackEntryCount = getSupportFragmentManager().getBackStackEntryCount();
    if(mPreviousBackStackCount >= backStackEntryCount) {
        mFragPositionTitleDisplayed.pop();
        if (backStackEntryCount == 0)
            getSupportActionBar().setTitle(R.string.app_name);
        else if (backStackEntryCount > 0) {
            getSupportActionBar().setTitle(mFragPositionTitleDisplayed.peek());
        }
        mPreviousBackStackCount--;
    }
    else{
        mFragPositionTitleDisplayed.push(title_name[position]);
        mPreviousBackStackCount++;
    }

}   

In the code shown we have the displayFragment() method. Here I display the fragment on the basis of option chosen from the navigation drawer.The variable position corresponds to the position of the item clicked from the ListView or RecyclerView in the navigation drawer. I set the actionbar title accordingly with getSupportActionBar.setTitle(title), where the title stores the appropriate title name.

Whenever we click the item from nav drawer a fragment is displayed depending on the item clicked to the user. But on the back end side this fragment is added to the backstack and the method onBackStachChanged(), gets hit. What I have done is that I have created a variable mPreviousBackStackCount and initialized it to 0. I have also created an additional stack which will store the action bar title names. Whenever I add a new fragment to the backstack, I add the corresponding title name to my created stack. On the opposite side whenever I press the back button onBackStackChanged() is called and I pop the last title name from my stack and set the title to the name derived by the peek() method of the stack.

Example:

Lets say our android backstack is empty:

Press Choice 1 from nav drawer: onBackStachChanged() is called and the Fragment 1 is added to android backstack, backStackEntryCount is set to 1 and Frag1 is pushed to my stack and size of mFragPositionTitleDisplayed becomes 1.

Press Choice 2 from nav drawer: onBackStachChanged() is called and the Fragment 2 is added to android backstack, backStackEntryCount is set to 2 and Frag2 is pushed to my stack and size of mFragPositionTitleDisplayed becomes 2.

Now we have 2 elements both in the android stack and my stack. When you press back button onBackStackChanged() is called and the value of backStackEntryCount is 1. The code enters the if part and pops out the last entry from my stack. So, the android backstack has only 1 fragment - "Fragment 1" and my stack has only 1 title - "Frag1". Now I just peek() the title from my stack and set the action bar to that title.

Remember: To set the action bat title use peek() and not pop() else your application will crash when you open more than 2 fragments and try to go back by pressing back button.