RecyclerView (horizontal) nested in BottomSheet preventing vertical scrolling

Question

I have a RecyclerView using a LinearLayoutManager with HORIZONTAL orientation, nested inside a FrameLayout using the BottomSheet Behavior.

When attempting to drag vertically across the RecyclerView, the BottomSheet doesn't respond to the drag event. Presumably this is because vertical scrolling is disabled for a LayoutManager with horizontal orientation.

I've tried overriding LinearLayoutManager.canScrollVertically() and returning true. This sort of works.. If you drag vertically in a very careful manner, the BottomSheet will respond. As soon as any horizontal movement is involved however, the BottomSheet stops responding to vertical drag events.

I'm not sure if overriding canScrollVertically() is the right approach here - it certainly doesn't feel right from a UX point of view.

I've also noticed that if I use a ViewPager rather than a RecyclerView with a horizontally oriented LayoutManager, the BottomSheet responds to vertical swipe events as desired.

Is there some other method of LayoutManager, RecyclerView, BottomSheet Behavior, or something else altogether that can help propagate the vertical scroll events on to the BottomSheet Behavior?

There's an example of the problem here:

https://github.com/timusus/bottomsheet-test (Problem can be reproduced with commit #f59a7031)

Just expand the first bottom sheet.

Answer 1

Where does the problem lies? In FrameLayout. BottomSheet works perfectly when put inside CoordinatorLayout. Then BottomSheet can pass it's scrolling state through CoordinatorLayout to other views put as direct children of CoordinatorLayout.

Why RecyclerView was not able to pass scroll state to BottomSheet? It is not a direct child of CoordinatorLayout. But there exists a way to pass them: RecyclerView must be in put in view that implements NestedScrollingParent and NestedScrollingChild. The answer to that is: NestedScrollView

So your fragment_sheetX.xml layouts should look like:

<?xml version="1.0" encoding="utf-8"?>
<android.support.v4.widget.NestedScrollView
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="#fff"
    android:orientation="vertical"
    android:fillViewport="true">

    <android.support.v7.widget.RecyclerView
        android:id="@+id/recyclerView"
        android:layout_width="match_parent"
        android:layout_height="match_parent"/>

</android.support.v4.widget.NestedScrollView>

Notice also android:fillViewport="true" as otherwise, your RecyclerView will not take whole height.

However it still will not work. Why? RecyclerView must be told to pass vertical scrolling to parent. How? The answer is recyclerView.setNestedScrollingEnabled(false);, but that is better described here.

Btw: MultiSheetView is a great feature and a very interesting approach to mobile UX design.