CODEWITHSUNDEEP
androidsavefragmentinstancestate
Francesco Rizzi
Francesco Rizzi

Reputation: 631

Android Fragments - Should we really save state?

I have implemented a simple activity with this code:

public class MainActivity extends AppCompatActivity implements Fragment_1.Operations{

Fragment_1 fragment_1;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

    setContentView(R.layout.fragmentactivity);
    fragment_1=(Fragment_1)getSupportFragmentManager().findFragmentByTag("fragment_1");
}
//called on buttonclick, fired from a button existing in R.layout.fragmentactivity
public void createFragment(View view){

    if (getSupportFragmentManager().findFragmentByTag("fragment_1")==null){

        fragment_1=new Fragment_1();

        FragmentTransaction transaction=getSupportFragmentManager().beginTransaction();

        transaction.add(R.id.fragmentactt,fragment_1,"fragment_1");
        transaction.commit();
        getSupportFragmentManager().executePendingTransactions();
    }
    else{

        fragment_1=(Fragment_1)getSupportFragmentManager().findFragmentByTag("fragment_1");
    }

    //Simply adding item to the listview contained in fragment_1.
    fragment_1.add("Project #1");
    fragment_1.add("Project #2");
    fragment_1.add("Project #3");
}

    //callback of interface "Operations"
    @Override
    public void buttonClicked() {

        FragmentTransaction transaction=getSupportFragmentManager().beginTransaction();

        if (fragment_1.isAdded()){

            transaction.remove(fragment_1);
            //transaction.addToBackStack(null);
            transaction.commit();
            getSupportFragmentManager().executePendingTransactions();
        }
    }
}

Well, the doubt came from the fact that no "onSaveInstanceState" needed to be implemented, everything got "saved" without any problems.

So, why should i use putfragment and getFragment? Do these methods need to be called in order to avoid that, when OS kills app process, they would be lost? This is the only reason i can imagine to force onSaveInstanceState and onRestoreInstanceState methods.

Any help is appreciated.

Upvotes: 0

Views: 201

Answers (1)

Alexandre Martin
Alexandre Martin

Reputation: 1502

Activity and fragment lifecycles are linked so when any callback method such as onResume is called for the activity, it is called for the fragment too.

putFragment and getFragment help the activity to manage its fragment child's lifecycle. The activity also has to save instance state.

In order to be activity independant, a fragment can manage his own instance state.

Upvotes: 2

Related Questions