Android fragment replace(...) on thread

Question

Can someone explain me why replacing fragment on thread causes sometimes blank space instead of showing the fragment on screen?

public void swapFragment(final CustomFragment fragment) {

    new Thread(new Runnable() {
        @Override
        public void run() {
            FragmentTransaction ft = activity.getFragmentManager().beginTransaction();
            ft.replace(R.id.fragment_container, fragment, fragment.getName());
            ft.addToBackStack(fragment.getName());

            ft.commit();
        }
    }).start();

}

Let me explain what is happening:

1) I have no fragment added inside my container.

2) I'm adding fragment A using this method - its working

3) Then I'm using this method to swap actual fragment A with my fragment B - its working

4) But when I'm trying to swap it with new instance (!!!) of fragment A it leaves blank space

I know that i can do it on main thread, but this is just an example. I'm dealing with different issue, but my issue is more complex to explain.

EDIT :

at point 4) I placed wrong fragment - it was ment to be "fragment A"

score 2 · Answer 1 · edited May 23 '17 at 12:07

You are swapping same Fragment B with its new instance.

Swapping operation will work only when source and destination fragments are of different classes.

I can defer this from answers this and question this

So, workaround would be :

Check if same fragment class is already added (isAdded()) or not, if not then swap() else use remove() and add() operation

public void swapFragment(final CustomFragment fragment) {

new Thread(new Runnable() {
    @Override
    public void run() {
        FragmentTransaction ft = activity.getFragmentManager().beginTransaction();
        if(!fragment.isAdded()) {
            ft.replace(R.id.fragment_container, fragment, fragment.getName());
            ft.addToBackStack(fragment.getName());

            ft.commitAllowingStateLoss();

        } else {
            ft.remove(R.id.fragment_container, fragment);
            ft.add(fragment);
            ft.addToBackStack(fragment.getName());

            ft.commitAllowingStateLoss();

    }
}).start();

}

Check if same fragment class is already added (isAdded()) then update its UI content, else swap()

public void swapFragment(final CustomFragment fragment) {

new Thread(new Runnable() {
    @Override
    public void run() {
         FragmentTransaction ft = activity.getFragmentManager().beginTransaction();
        if(!fragment.isAdded()) {
            ft.replace(R.id.fragment_container, fragment, fragment.getName());
            ft.addToBackStack(fragment.getName());

            ft.commitAllowingStateLoss();
        } else {
            // logic to update UI of same instance
        }
    }
}).start();

}

Still, exact solution is awaited for this question :)

Hope this will help you

Android fragment replace(...) on thread

EDIT :

1 Answers1