How can I add a shadow to bottom sheet view?

Question

As of now, with the official bottom sheet component from the Android design library implemented the top edge doesn't show a shadow. But for what I've seen in various mockups and in the Material Design specs, the bottom sheet include a discrete shadow of some sort.

I think the shadow would help distant the bottom sheet from the main layout, especially if there's a peek value set and/or the bottom sheet is always visible. Otherwise it just will blend together with the main layout and its items.

I've tried both ViewCompat.setElevation(bottomSheet, 5); and setting android:elevation="5dp" to the view in the XML, without success.

Answer 1

I know that a shadow shape doesn't have the same appearance as an elevation - but at least give it a try. The trick is to use app:layout_anchor to clip the shadow to the bottom sheet.

activity_main.xml

<android.support.design.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">

<MapView
    android:id="@+id/map"
    android:layout_width="match_parent"
    android:layout_height="match_parent" />

<View
    android:id="@+id/shadow"
    android:layout_width="match_parent"
    android:layout_height="16dp"
    android:background="@drawable/shape_gradient_top_shadow"
    app:layout_anchor="@id/bottom_sheet" />

<FrameLayout
    android:id="@+id/bottom_sheet"
    android:layout_width="match_parent"
    android:layout_height="200dp"
    android:clipToPadding="false"
    app:layout_behavior="android.support.design.widget.BottomSheetBehavior" />

</android.support.design.widget.CoordinatorLayout>

shape_gradient_top_shadow.xml

<shape xmlns:android="http://schemas.android.com/apk/res/android">
<gradient
    android:angle="90"
    android:endColor="@android:color/transparent"
    android:startColor="#64000000"/>
</shape>

Looks like this:

EDIT

Get an even better result with a custom ShadowView:

• Post from Roman Nurik on this topic: https://plus.google.com/+RomanNurik/posts/2QvHVFWrHZf
• Gist of the ShadowView based on Roman Nurik's solution: https://gist.github.com/MariusBoepple/bf869e02541cd4750550e88fa07b5ddd

Then you can do the following:

<ShadowView
    android:id="@+id/shadow"
    android:layout_width="match_parent"
    android:layout_height="16dp"
    android:gravity="bottom"
    app:layout_anchor="@id/bottom_sheet" />

Answer 2

For API Level 21 and higher, set the following in the parent view. You can also try in the rootview of the bottomsheet (I have not tried it in the root view)

android:background="@android:color/white"
android:elevation="16dp"

If no background then can use

android:outlineProvider="bounds"

For example, I have my sheet inside a nested scroll view

<android.support.v4.widget.NestedScrollView
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:clipToPadding="false"
  app:layout_behavior="android.support.design.widget.BottomSheetBehavior"
        android:elevation="16dp"
        android:outlineProvider="bounds"
        >

    <include layout="@layout/bottomsheet_1" />

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