update TextView in fragment A when clicking button in fragment B

Question

I have two fragments sitting side by side in the same activity. When I touch a button in the right fragment (fragment B), I need a TextView in the left fragment to update (f

Answer 1

You can define an interface in Fragment B and implement it on the MainActivity. Then on the callback method (onClickOnB in this case) set the text on the TextView. You should obtain a reference of the TextView in the Activity's onCreate() after setContentView(). This works because Fragment A is static. Otherwise, you can create a public method inside Fragment A so you can set the text from inside the callback by getting a reference of Fragment A and calling such method.

Fragment B

public class FragmentB extends Fragment implements onClickListener{
ClickOnB listener;
public void setOnFragmentBClickListener(ClickOnB listener){
this.listener = listener;

}

@Override

public void onClick(View v){
//stringMessage is a `String` you will pass to `Fragment` A to update its `TextView`
listener.onClickOnB(stringMessage);
}

interface ClickOnB{
public void onClickOnB(String message);
}

}

MainActivity

public class MainActivity extends Activity implements ClickOnB{
@Override   
protected onCreate(Bundle savedInstanceState){

//Get a reference of `Fragment` B somewhere in your code after you added it dynamically and set the listener.
((FragmentB)getFragmentManager().findFragmentByTag("FragmentB")).setOnFragmentBClickListener(this);

}

@Override
public void onClickOnB(String message){

//Set the text to the `TextView` here (I am assuming you get a reference of the `TextView` in onCreate() after inflating your layout.

mTextView.setText(message);

}
}