android 背景设置报错 tag requires a 'drawable' attribute or child tag defining a drawable

今天本来只是想实现一个简单的按下 ImageButton 背景变颜色的功能，结果碰到 tag requires a 'drawable' attribute or child tag defining a drawable 的错误。这句话的意思很简单，就是说 item 标签下需要 drawable 属性。在逛了无数国内论坛无果后，我尝试进了一个英文网站，结果如醍醐灌顶，深深的感觉到国内和国外的差距。

The problem here is that you cannot define the background color using a color selector, you need a drawable selector. So, the necessary changes would look like this:

你不能将颜色选择器用在 background 上，应该使用 drawable selector，所以你应该这样修改(假设文件名为 selector.xml)：

<xml version="1.0" encoding="utf-8"?>
    <xmlns:android="http://schemas.android.com/apk/res/android">
  
  android:state_pressed="true"
  android:drawable="@drawable/selected_state"  />
  awable/selected_state"/>

**You would also need to move that resource to the drawable directory where it would make more sense since it's not a color selector per se.

Then you would have to create the res/drawable/selected_state.xml file like this:**

  <xml version="1.0" encoding="UTF-8"?>
    xmlns:android="http://schemas.android.com/apk/res/android"
  android:shape="rectangle">
    android:color="@color/semitransparent_white"  />

其实这种方法将 selector 和颜色的定义分开了 我们可以将 selector 和 shape 的定义放在一起：

<xml version="1.0" encoding="UTF-8"?>
   <xmlns:android="http://schemas.android.com/apk/res/android">
    android:state_pressed="true">
  
    android:color="#F1F1F1"/>
  
  
    android:state_selected="true">
  
    android:color="#F1F1F1"/>