android 写 selector.xml 时的注意事项

原文链接：http://developer.android.com/guide/topics/ui/controls/button.html

<?xml version="1.0" encoding="utf-8"?><selector xmlns:android="http://schemas.android.com/apk/res/android">    <item android:drawable="@drawable/button_pressed"          android:state_pressed="true" />    <item android:drawable="@drawable/button_focused"          android:state_focused="true" />    <item android:drawable="@drawable/button_default" /></selector>

Note: The order of the <item> elements is important. When this drawable is referenced, the <item>elements are traversed in-order to determine which one is appropriate for the current button state. Because the default bitmap is last, it is only applied when the conditions android:state_pressed andandroid:state_focused have both evaluated as false.

注意： <item> 元素的顺序非常重要。当这个 drawable 被引用时，<item> 元素会以中序(in-order)的方式被遍历，以确定哪个比较恰当地对应当前的 button 状态。由于 默认bitmap 是最后面的，只有当条件 android:state_pressed 和 android:state_focused 同时为 false 时，才会使用到它