Home / Questions / 31511
Accepted
Mario López Batres
Asked: 2020-11-04 01:51:11 +0800 CST 2020-11-04 01:51:11 +0800 CST

getFragmentManager null the second time

  • 772

Good morning, I've been programming on Android for a few weeks and I'm having certain problems with the use of getFragmentManager.

I have read post about the termination of activities and this is what I have come up with:

Quote Answer Stack Over Flow English 1

Also onDestroy() is not a destructor. It doesn't actually destroy the object, it's just a method that returns a certain state.

in addition to this:

Quote Answer Stack Over Flow English 2

Consider then that your application will be in the background and then die. When you come back Android will remember that you had Fragments, for example A, B and C and the manager will recreate them and then add them.

I call the method 2 times from one of my activities, and the second time (after doing a getActivity.finish(), recreating the activity and returning to the method from the previous fragment), it points to null.

The point of failure is:

        private BroadcastReceiver estadoIAReceiver = new BroadcastReceiver() {
    //Cuando cambia el estado de indoor atlas actualizo la interfaz con sus propiedades
    @Override
    public void onReceive(Context context, Intent intent) {
        Log.i("VFragment", "Cambio estado IA");

        //Ejecutar metodo de un fragment desde una actividad
        infoF = (InformacionFragment) getFragmentManager().findFragmentById(R.id.posicionamiento_layout); // <<--- AQUI!!!
        infoF.actualizaInfoEstadoIA();
        infoF.onResume();
    }
};

and infoFis what it givesnull

infoF = (InformacionFragment) getFragmentManager().findFragmentById(R.id.posicionamiento_layout);

this brings me backnull

I've been debugging the app and re-creating activities and fragmentsit's correct, so it shouldn't point to null.

My question is:

With what I read, I have intuited that it is trying to point to the old fragmentone (1 time executed), since finish() does not really delete 100% Activity(and I assume it fragmentsdoes not either). How could I fix it?

java

2 Answers

  1. Best Answer

    I finally solved my problem. Apparently, when doing a finish() you don't completely destroy the activity, but rather some information is saved in savedInstanceState, and therefore when trying to point to the Fragment, it returns null.

    The solution is the next:

    • Just create a new variable of type Bundle as a global variable:

      SaveData Bundle;

    • To store the savedInstanceState information

      savedData = savedInstanceState;

    • And check that said variable is not null before calling getFragmentManager

      if (DataSaved != null) infoF = (FragmentInformation) getFragmentManager().findFragmentById(R.id.positioning_layout);

    • 1

  2. When calling , the Activity is completely destroyed, but first the onSaveInstanceState()finish() method is called (if it is implemented) , which is where you can save desired values, as an example it saves the user value:

      @Override
    public void onSaveInstanceState(Bundle savedInstanceState) {

        savedInstanceState.putString("username", user);

        super.onSaveInstanceState(savedInstanceState);
    }

    in this case it can also be used to know if an instance previously existed, and also the saved value is obtained through onSaveInstanceState() , example:

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


        if (savedInstanceState == null) {
            //Obtiene valor guardado en onSavedInstanceState, y necesitado en el Fragment
            String user = getIntent().getExtras().getString("username");

            FragmentTransaction transaction = getSupportFragmentManager().beginTransaction();
            transaction.replace(R.id.content, MyFragmento.newInstance(user));
            transaction.commit();
        }
    }
}

    onSaveInstanceState() Called to retrieve the per-instance state of an activity before it is killed so that the state can be restored in either onCreate(Bundle) or onRestoreInstanceState(Bundle) (the Bundle populated by this method will be passed to both).

    • 0