James Pizzurro James Pizzurro - 5 months ago 91
Android Question

Detecting when AppBarLayout/CollapsingToolbarLayout is completely expanded

I have a fragment that uses the new CoordinatorLayout/AppBarLayout/CollapsingToolbarLayout paradigm, and I'd like to be able to detect when the collapsing toolbar is fully expanded so that I can perform an operation on the entire fragment it's in, e.g. popping the fragment off the stack and going to a new one, dismissing the fragment. I have the dismissing code working, I just need to know when and when not to use it.

I've experimented a bit with AppBarLayout.OnOffsetChangedListener, but didn't have much luck. Is there a way to use it to determine when things are completely expanded, or is there a more preferred method someone knows about?

Thanks in advance!

EDIT:
I also see there are a couple implementations for AppBarLayout.setExpanded(...), however not AppBarLayout.getExpanded() or something similar, so I'm stumped there too.

Answer

It doesn't look like there's anything in the APIs, but the following seems to be working for me. It might need testing.

boolean fullyExpanded =
    (appBarLayout.getHeight() - appBarLayout.getBottom()) == 0;

Edit: The above solution does seem to work, but since I wanted to test this condition when the appbar was scrolled, I ended up using the following solution with OnOffsetChangedListener.

class Frag extends Fragment implements AppBarLayout.OnOffsetChangedListener {

    private boolean appBarIsExpanded = true;
    private AppBarLayout appBarLayout;

    @Override 
    public void onActivityCreated(Bundle state) {
        super.onActivityCreated(state);
        appBarLayout = (AppBarLayout) getActivity().findViewById(R.id.app_bar);
    }

    @Override
    public void onResume() {
        super.onResume();
        appBarLayout.addOnOffsetChangedListener(this);
    }

    @Override
    public void onStop() {
        super.onStop();
        appBarLayout.removeOnOffsetChangedListener(this);
    }

    @Override
    public void onOffsetChanged(AppBarLayout appBarLayout, int verticalOffset) {
        appBarIsExpanded = (verticalOffset == 0);
    } 

}
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