CoordinatorLayout and AppBarLayout elevation

This is actually an implementation detail of CollapsingToolbarLayout, as seen in the source code:

if (Math.abs(verticalOffset) == scrollRange) {  // If we have some pinned children, and we're offset to only show those views,  // we want to be elevate  ViewCompat.setElevation(layout, layout.getTargetElevation());} else {  // Otherwise, we're inline with the content  ViewCompat.setElevation(layout, 0f);}

Which removes the elevation when the CollapsingToolbarLayout is showing non-pinned elements - by default, it'll only have elevation when only pinned children are visible.

the reason is above,try this to solve:

appBarLayout.addOnOffsetChangedListener(new AppBarLayout.OnOffsetChangedListener() {        @Override        public void onOffsetChanged(AppBarLayout appBarLayout, int verticalOffset) {            //some other code here            ViewCompat.setElevation(appBarLayout, The Elevation In Px);        }    });

The solution is to use app:elevation=0dp to remove the default elevation and set android:translationZ to the elevation you want.

Note : The code below uses the latest AndroidX / Material libraries and might not work if you're using the old support library

<com.google.android.material.appbar.AppBarLayout    android:layout_height="wrap_content"    android:layout_width="match_parent"    android:translationZ="8dp"    app:elevation="0dp">    <!--      * `app:elevation=0dp` disables the default shadow that is automatically added on      scroll ; other values e.g. `6dp` are ignored despite what the official doc says      (see below)      * so instead we're using `android:translationZ` to add a shadow with a custom      elevation    -->

The documentation for AppBarLayout # setTargetElevation() states that you can set a custom elevation value using the app:elevation attribute, but it didn't work for me for values greater than 0dp, so I'm using translationZ as a workaround.