Question

I have a layout with two Fragments in it. Second one loads dynamically.

Fragment fg = EmptyRightFrag.newInstance();
        getFragmentManager().beginTransaction().add(R.id.right_frag, fg)
            .commit();

Then this second frame replaces with another ‘Fragment’.

    Fragment fg = MyClass.newInstance();
    getFragmentManager().beginTransaction().replace(R.id.right_frag, fg)
                .commit();

Finally I need to initialize the second Fragment by calling:

MyClass field = ((MyClass)getFragmentManager().findFragmentById(R.id.right_frag));

But here I do get java.lang.ClassCastException stating EmptyRightFrag cannot be casted to MyClass.

Answer 1

Where are you calling findFragmentById()? Directly after you added it?

The docs for commit() says this:

Schedules a commit of this transaction. The commit does not happen
immediately; it will be scheduled as work on the main thread to be
done the next time that thread is ready.

This means that the Fragment will not be added for a while (at least not before your method has returned). Anyways you should probably not handle initialization this way, it’s better to let the Fragment take care of that in onCreate() or something.