onBackPressed and call refresh function android

Lester :

I want to refresh just one fragment that in an tab bar activity when I press the back button. How can i achieve that? What I tried

java.lang.NullPointerException: Attempt to invoke virtual method 'android.support.v4.app.FragmentTransaction android.support.v4.app.FragmentManager.beginTransaction()' on a null object reference

Fragment Profile

public void refreshFragment(){
    FragmentTransaction ft = getFragmentManager().beginTransaction();
    ft.detach(this).attach(this).commit();
}

Edit profile activity

@Override
public void onBackPressed() {
    super.onBackPressed();
    FragmentProfile fragment = new FragmentProfile();
    fragment.refreshFragment();
}

Wan :

You can use SharedPreferences to do this.

Step 1: create a constants class.

public class Constants {
    public static final String REFRESH = "refresh_content";
}

Step 2: put boolean to the constants.REFRESH on Edit Profile Activity,

private SharedPreferences pref;

@Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
    pref = PreferenceManager.getDefaultSharedPreferences(getContext());

    return inflater.inflate(R.layout.fragment_rostering, container, false);
}

public void onBackPressed() {
    SharedPreferences.Editor editor = pref.edit();
    editor.putBoolean(Constants.REFRESH, true);
    editor.commit();
    super.onBackPressed();
}

Step 3: Call refresh function on the onResume on Fragment Profile

private SharedPreferences pref;

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState) {

    pref = PreferenceManager.getDefaultSharedPreferences(getContext());

    return inflater.inflate(R.layout.fragment_profile, container, false);
}

@Override
public void onResume() {
    super.onResume();
    if(pref.getBoolean(Constants.REFRESH, false)){
        SharedPreferences.Editor editor = pref.edit();
        editor.putBoolean(Constants.REFRESH, false);
        editor.commit();
        refreshFragment();
    }
}