Detecting when AppBarLayout/CollapsingToolbarLayout is completely expanded

Question

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 1

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);     }   } 

Answer 2

My solution is based on creating a custom view. First create a class extending the native AppBarLayout:

public class CustomAppBar extends AppBarLayout { ....

Then inside the class set an addOnOffsetChangedListener like this:

this.addOnOffsetChangedListener...

You can do the above by setting in the constructor or maybe by calling a method inside the constructor. So you need the constructor, remember to use the constructor with 2 params to be able to added to the xml:

public CustomAppBar(Context context, AttributeSet attrs) {
        super(context, attrs);
//You can set the listener here or maybe call the method that set the listener
}

Then we have to get access to the state of the view, so create a private boolean inside your custom view class, and set it to true or false if your view start expanded or collapsed, in this case my view is by default expanded:

private boolean isExpanded = true;

Now you have to update the state of that boolean:

this.addOnOffsetChangedListener(new AppBarLayout.OnOffsetChangedListener() {
            @Override
            public void onOffsetChanged(AppBarLayout appBarLayout, int verticalOffset) {
                if (verticalOffset == 0) {
                    isExpanded = true;
                } else {
                    isExpanded = false;
                }
            }
        });

Next step is to get the state of the boolean by using a getter inside the CustomAppBar class

public boolean isExpanded() {
        return isExpanded;
    }

The next is go to your xml, use your custom view there, then in the Acivity or Fragment get the view and use the method to know the AppBar status