Android toolbar elevation when scrolling

The accepted answer is outdated. Now there is inbuilt functionality to do this. I am pasting the whole layout code so it will help you to understand.

You just need to use CoordinatorLayout with AppBarLayout. This design pattern is called Lift On Scroll and can be implemented by setting app:liftOnScroll="true" on your AppBarLayout.

Note: the liftOnScroll attribute requires that you apply the @string/appbar_scrolling_view_behavior layout_behavior to your scrolling view (e.g., NestedScrollView, RecyclerView, etc.).

<?xml version="1.0" encoding="utf-8"?>
<androidx.coordinatorlayout.widget.CoordinatorLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity"
    android:background="@color/default_background">

    <com.google.android.material.appbar.AppBarLayout
        android:id="@+id/appbar"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        app:liftOnScroll="true">

        <androidx.appcompat.widget.Toolbar
            android:id="@+id/toolbar"
            android:layout_width="match_parent"
            android:layout_height="?attr/actionBarSize"
            android:background="@color/default_background" />

    </com.google.android.material.appbar.AppBarLayout>

    <androidx.recyclerview.widget.RecyclerView
        android:id="@+id/list_recycler_view"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:layout_below="@+id/appbar"
        app:layout_behavior="@string/appbar_scrolling_view_behavior"
        android:orientation="vertical" />

</androidx.coordinatorlayout.widget.CoordinatorLayout>

Refered this documentation https://github.com/material-components/material-components-android/blob/master/docs/components/AppBarLayout.md

This is a good question but none of the existing answers are good enough. Calling getTop() is absolutely not recommended as it's very unreliable. If you look at newer versions of Google apps that follow Material Design Refresh (2018) guidelines, they hide the elevation at the beginning and immediately add it as user scrolls down and hide it again as user scrolls and reaches the top again.

I managed to achieve the same effect using the following:

val toolbar: android.support.v7.widget.Toolbar? = activity?.findViewById(R.id.toolbar);

recyclerView?.addOnScrollListener(object: RecyclerView.OnScrollListener() {
    override fun onScrolled(recyclerView: RecyclerView, dx: Int, dy: Int) {
        super.onScrolled(recyclerView, dx, dy);

        if(toolbar == null) {
            return;
        }

        if(!recyclerView.canScrollVertically(-1)) {
            // we have reached the top of the list
            toolbar.elevation = 0f
        } else {
            // we are not at the top yet
            toolbar.elevation = 50f
        }
    }
});

This works perfectly with vertical recycler views (even with tab view or other recycler views inside them);

A couple of important notes:

• Here I'm doing this inside a fragment hence activity?.findViewById...
• If your Toolbar is nested inside an AppBarLayout, then instead of applying elevation to Toolbar, you should apply it to the AppBarLayout.
• You should add android:elevation="0dp" and app:elevation="0dp" attributes to your Toolbar or AppBarLayout so that the recycler view doesn't have elevation at the beginning.

EDIT As pointed out in the comments, my answer is now outdated, see https://stackoverflow.com/a/58272283/4291272

---

Whether you are using a CoordinatorLayout or not, a RecyclerView.OnScrollListener seems like the right way to go as far as the elevation is concerned. However, from my experience recyclerview.getChild(0).getTop() is not reliable and should not be used for determining the scrolling state. Instead, this is what's working:

private static final int SCROLL_DIRECTION_UP = -1;
// ...
// Put this into your RecyclerView.OnScrollListener > onScrolled() method
if (recyclerview.canScrollVertically(SCROLL_DIRECTION_UP)) {
   // Remove elevation
   toolbar.setElevation(0f);
} else {
   // Show elevation
   toolbar.setElevation(50f);
}

Be sure to assign a LayoutManager to your RecyclerView or the call of canScrollVertically may cause a crash!

I have a RecyclerView in my fragment. I could achieve similar effect using code below:

It is not the Smartest way and you can wait for better answers.

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
        Bundle savedInstanceState) {

    // Initial Elevation
    final Toolbar toolbar = (Toolbar) getActivity().findViewById(R.id.toolbar);
    if(toolbar!= null)
        toolbar.setElevation(0);

    // get initial position
    final int initialTopPosition = mRecyclerView.getTop();

    // Set a listener to scroll view
    mRecyclerView.addOnScrollListener(new RecyclerView.OnScrollListener() {

        @Override
        public void onScrollStateChanged(RecyclerView recyclerView, int newState) {
            super.onScrollStateChanged(recyclerView, newState);
        }

        @Override
        public void onScrolled(RecyclerView recyclerView, int dx, int dy) {
            super.onScrolled(recyclerView, dx, dy);

            if(toolbar!= null && mRecyclerView.getChildAt(0).getTop() < initialTopPosition ) {
                toolbar.setElevation(50);
            } else {
                toolbar.setElevation(0);
            }
        }
    });
}