Return to a previous Fragment from any Fragment

Question

I have a main activity in which are called some Fragments:

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_listas);

    FragmentManager fm = getSupportFragmentManager();
    FragmentTransaction ft = fm.beginTransaction();

    FragmentUm fragment_um = new FragmentUm();
    ft.add(R.id.fragment, fragment_um).commit();
}

When loading fragment_um in this Activity I have a Recyclerview where I click on an item that can direct me to activity_details or call fragment_two:

FragmentManager fm = getFragmentManager();
FragmentTransaction ft = fm.beginTransaction();
FragmentDois fragment_dois = new FragmentDois();

ft.addToBackStack(null);
ft.replace(R.id.fragment, fragment_dois).commit();

By loading fragment_two I have a Recyclerview that by clicking on an item in the list can direct me to fragment_tres or to activity_details. Fragment_tres I have the same situation.

In the manifest the main Activity is configured to show the home button on Toolbar:

android:parentActivityName=".MainActivity"

However, if you have fragment_two clicked on Activity and click the home button, I cannot go back to fragment_one. The same thing happens if you are in fragment_tres and click on the home button, I cannot go back to fragment_dois.

I tried to use getFragmentManager().popBackStack() or getFragmentManager().popBackStackImmediate() within the onOptionsItemSelected(MenuItem item) but it didn’t work out.

My question is, what do I have to do to get back to the previous Fragment from any of them?

I made some changes to the code:

In the main Activity I use the onBackPressed() class for when clicking on the home icon, through onOptionsItemSelected(Menuitem item), to go back to the previous Fragment:

@Override
public void onBackPressed(){
    FragmentManager fm = getSupportFragmentManager();
    if (fm.getBackStackEntryCount() > 0) {
        fm.popBackStack();
    }
}

I have removed from the manifest the configuration I mentioned earlier. In onViewCreated from Fragments I implemented this code to programmatically display the home icon in Actionbar. In Fragment 1 it is false and in the other true:

ActionBar actionbar=((AppCompatActivity)getActivity()).getSupportActionBar();
    actionbar.setDisplayHomeAsUpEnabled(true);

It is working, however it is showing an alert that getSupportActionBar and setDisplayHomeAsUpEnabled can generate a Nullpointerexception. You can fix it?

Answer 1

Apparently you’re right, instead of using getFragmentManager().popBackStack() and getFragmentManager().popBackStackImmediate() within the onOptionsItemSelected(MenuItem item), utilize getActivity().getFragmentManager().popBackStack(), this solution worked in questioning Manage back button between Ragments

But this function is to be used in ActionBar and not on the button Home.

Answer 2

I do not know if it is the most correct way to solve the problem I pointed out, but I solved it in the following way:

In the Factions includes:

@Override
public void onAttach(Context context) {

    super.onAttach(context);

    if (context instanceof Activity){
        mActivity =(Activity) context;
    }
}

public static AppCompatActivity getAppCompActivity(Context context) {
    if (context == null)
        return null;
    if (context instanceof AppCompatActivity) {
        return (AppCompatActivity) context;
    }
    return null;
}

And still in the Events in onViewCreated:

@Override
public void onViewCreated(@NonNull View view, @Nullable Bundle savedInstanceState) {
    super.onViewCreated(view, savedInstanceState);

    ActionBar actionBar = getAppCompActivity(mActivity).getSupportActionBar();
    if (actionBar != null) {
        actionBar.setDisplayHomeAsUpEnabled(true);
    }

}

In Mainactivity

@Override
public boolean onOptionsItemSelected(MenuItem item) {
    int id = item.getItemId();

    if (id == android.R.id.home){
        onBackPressed();
    }
}

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

I can get back between Ragments and no more Nullpointerexception alert. Perhaps still fit improvements, but at the moment met my needs.