How to Trigger a Scroll Behavior on a Toolbar inside a CoordinatorLayout

Question

I have a [PDFView][1] as the direct child of a CoordinatorLayout as in:

I tried to add app:layout_behavior="@string/appbar_scrolling_view_behavior" to the PDFView but it's not compatible so it isn't triggering any scroll behavior on the Toolbar .

The Toolbar has app:layout_scrollFlags="scroll|enterAlways|snap" and I know it works because I already tested it with a NestedScrollView instead of the PDFView .

So I want to achieve this programatically, but I can't find any documentation on how to let the CoordinatorLayout know there's a scroll going on and it should animate the Toolbar going away.

How can I trigger this behavior programatically? The PDFView has a ScrollListner I just don't know how to connect it to the CoordinatorLayout .

Answer 1

First the PDF view does not implement NestedScrollingChild2 , so you need to implement it. After implementing it , you have to implement five methods. Also create an instance NestedScrollingChildHelper and delegate the implemented methods to this instance.

View subclasses should instantiate a final instance of this class as a field at construction. For each View method that has a matching method signature in this class, delegate the operation to the helper instance in an overridden method implementation. This implements the standard framework policy for nested scrolling.

Let me know if it works.