android.support.v4.app.getFragmentManager() returns null?

Question

This is my Stacktrace:

FATAL EXCEPTION: main
java.lang.NullPointerException
at com.example.test.fragments.LoadingFragment$1.run(LoadingFragment.java:66)
at a         


        

Answer 1

Replace this getFragmentManager() with this getSupportFragmentManager() and also make sure that your activity extends FragmentActivity

Answer 2

From android.support.v4.app.Fragment source:

// The fragment manager we are associated with.  Set as soon as the
// fragment is used in a transaction; cleared after it has been removed
// from all transactions.
FragmentManagerImpl mFragmentManager;

Apparently getFragmentManager() returns support version of fragment manager but only during a transaction (or parent fragment's child fragment manager).

I'm going to use this:

public FragmentManager getHostFragmentManager() {
    FragmentManager fm = getFragmentManager();
    if (fm == null && isAdded()) {
        fm = ((AppCompatActivity)getActivity()).getSupportFragmentManager();
    }
    return fm;
}

Answer 3

CASE: When you need to call Fragment(Child fragment) from another Fragment(Parent Fragment)

always use getChildFragmentManager() instead of getFragmentManager() inside your Parent Fragment.

Answer 4

After cleaning and rebuilding my project aswell as restarting my testing device, this worked again somehow.