Android5.0Android：高程适用于视图，但不适用按钮？

Question

在SDK管理器的Android 5.0示例中，有ElevationBasic示例。它显示了两个view对象：一个圆和一个正方形。圆圈的android:elevation设置为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>

在Nexus9上，按原样运行示例，我们在圆圈上得到一个阴影：

如果我们将widget类更改为button，保留所有其他属性不变，则会丢失圆圈上的阴影：

从昨天的问题中可以看出，我们如何让android:levation在按钮上获得荣誉？是否有一些android:AllowElevationToWorkasDocumented=“true”值需要放入主题或其他内容中？

Answer 1

Material下的默认按钮样式有一个StateListAnimator，它控制android:elevation和android:translationz属性。您可以删除现有的动画器，也可以使用android:statelistanimator属性设置自己的动画器。

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

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

默认动画器在button_state_list_anim_material.xml中定义。以下示例显示了启用和按下状态：

<?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>