设置background属性使用selector的时候内置?attr报错的解决方案

Posted 2020-08-19 dongweiq

当我们设置background属性的时候可以设置background="@color/black"

也可以设置 background="@drawable/selector"

然后selector我们可以这样设置

<?xml version="1.0" encoding="utf-8"?>
<selector xmlns:android="http://schemas.android.com/apk/res/android">
    <!-- 没有焦点时的背景图片 -->
    <item android:drawable="@color/colorPressed" android:state_pressed="true"/>
    <item android:drawable="@color/colorPressed" android:state_focused="true"/>
    <item android:drawable="@color/colorPressed" android:state_selected="true"/>
    <item android:drawable="@color/black" android:state_focused="false" android:state_pressed="false" android:state_selected="false"/>
</selector>

但是当我们设置了属性来设置这个颜色的时候就会遇到崩溃
比如我们这样

<?xml version="1.0" encoding="utf-8"?>
<selector xmlns:android="http://schemas.android.com/apk/res/android">
    <!-- 没有焦点时的背景图片 -->
    <item android:drawable="@color/colorPressed" android:state_pressed="true"/>
    <item android:drawable="@color/colorPressed" android:state_focused="true"/>
    <item android:drawable="@color/colorPressed" android:state_selected="true"/>
    <item android:drawable="?attr/backgroundColorValue" android:state_focused="false" android:state_pressed="false" android:state_selected="false"/>
</selector>

运行的话会直接崩溃，报错的原因是无法获取到对应的drawable对象，至于为什么无法将颜色转换成对应的drawable我也不清楚，既然不能转换那我们可以手动转换
解决方案：
手动创建一个shape.xml，如下：

<?xml version="1.0" encoding="utf-8"?>
<shape xmlns:android="http://schemas.android.com/apk/res/android"
       android:shape="rectangle">
    <solid android:color="?attr/backgroundColorValue" />
</shape>

然后我们再到selector中引用这个drawable就可以了

<?xml version="1.0" encoding="utf-8"?>
<selector xmlns:android="http://schemas.android.com/apk/res/android">
    <!-- 没有焦点时的背景图片 -->
    <item android:drawable="@color/colorPressed" android:state_pressed="true"/>
    <item android:drawable="@color/colorPressed" android:state_focused="true"/>
    <item android:drawable="@color/colorPressed" android:state_selected="true"/>
    <item android:drawable="@drawable/shape" android:state_focused="false" android:state_pressed="false" android:state_selected="false"/>
</selector>