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?
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>