findFragmentByTag() returns null after perform a FragmentTransaction using replace() method

Question

My Android app consists three fragments: A, B and C. They\'re loaded in the two containers defined in the MainActivity layout.

When th

Answer 1

Be sure you are adding or replacing the fragment in the proper way

Next statement will add the fragment but it will return null when using getFragmentManager().findFragmentByTag(tag):

transaction.add(R.id.mainContent, fragment);


This way it will work;

transaction.add(R.id.mainContent, fragment, tag);

Answer 2

I'll start by apologising since I'm still very new myself...

I think the problem may be in the declaration of the fragmentTag static String not properly getting access from the class's instances, just change that line to:

private final static String FRAGMENT_TAG = "FRAGMENTB_TAG"; // using uppercase since it's a constant

Also, I would be more explicit when declaring instances, for example:

public void buttonListener(View v){

    FragmentTransaction ft = getFragmentManager().beginTransaction();
    ft.replace(R.id.right_container, new FragmentB(), FRAGMENT_TAG);
    ft.commit();

    FragmentB fragB = (FragmentB) getFragmentManager().findFragmentByTag(FRAGMENT_TAG);
    fragB.testView();
}

I hope you get this sorted, as I seen this question posted earlier and was surprised that it hadn't got any activity yet.

Also, here are a couple of links to the android documentation on replace:

Android Training - Replace

Android Reference - Replace