Android 5.0 android:elevation Works for View, but not Button?

android, android-5.0-lollipop

Solution

The default Button style under Material has a StateListAnimator that controls the `android:elevation` and `android:translationZ` properties. You can remove the existing animator or set your own using the `android:stateListAnimator` property.

<Button
    ...
    android:stateListAnimator="@null" />

<Button
    ...
    android:stateListAnimator="@anim/my_animator" />

The default animator is defined in button_state_list_anim_material.xml. Here is a sample showing the enabled and pressed states:

<?xml version="1.0" encoding="utf-8"?>
<selector xmlns:android="http://schemas.android.com/apk/res/android">
    <item android:state_pressed="true" android:state_enabled="true">
        <set>
            <objectAnimator android:propertyName="translationZ"
                            android:duration="@integer/button_pressed_animation_duration"
                            android:valueTo="@dimen/button_pressed_z_material"
                            android:valueType="floatType"/>
            <objectAnimator android:propertyName="elevation"
                            android:duration="0"
                            android:valueTo="@dimen/button_elevation_material"
                            android:valueType="floatType"/>
        </set>
    </item>
    <!-- base state -->
    <item android:state_enabled="true">
        <set>
            <objectAnimator android:propertyName="translationZ"
                            android:duration="@integer/button_pressed_animation_duration"
                            android:valueTo="0"
                            android:startDelay="@integer/button_pressed_animation_delay"
                            android:valueType="floatType"/>
            <objectAnimator android:propertyName="elevation"
                            android:duration="0"
                            android:valueTo="@dimen/button_elevation_material"
                            android:valueType="floatType" />
        </set>
    </item>
    ...
</selector>

Problem

In the Android 5.0 samples from the SDK Manager, there is the `ElevationBasic` sample. It shows two `View` objects: a circle and a square. The circle has `android:elevation` set to `30dp`: ``` <?xml version="1.0" encoding="utf-8"?> <!-- Copyright 2014 The Android Open Source Project Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at http://www.apache.org/licenses/LICENSE-2.0 Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License. --> <FrameLayout xmlns:android="http://schemas.android.com/apk/res/android" xmlns:tools="http://schemas.android.com/tools" android:layout_width="match_parent" android:layout_height="match_parent"> <View android:id="@+id/floating_shape" android:layout_width="80dp" android:layout_height="80dp" android:layout_marginRight="40dp" android:background="@drawable/shape" android:elevation="30dp" android:layout_gravity="center"/> <View android:id="@+id/floating_shape_2" android:layout_width="80dp" android:layout_height="80dp" android:layout_marginLeft="25dp" android:background="@drawable/shape2" android:layout_gravity="center"/> </FrameLayout> ``` On a Nexus 9, running the sample as-is, we get a drop shadow on the circle: If we change the widget class to `Button`, leaving all other attributes as-is, we lose the drop shadow on the circle: The questions: Why is the `android:elevation` behavior changing? It cannot be due to the background, because it is the same background in both cases. Which classes support `android:elevation`, and which do not? For example, using `TextView` instead of `View` or `Button` still gives us the drop shadow, so this change in behavior is not introduced at the `TextView` level, but rather at the `Button` level. As seen in this question from yesterday, how do we get `android:elevation` to be honored on a `Button`? Is there some `android:allowElevationToWorkAsDocumented="true"` value that we have to put in a theme or something?

Original source