本文实例讲述了Android编程之selector下设置背景属性值的方法。，具体如下：
在res/drawable文件夹新增一个文件，此文件设置了图片的触发状态，你可以设置 state_pressed，state_checked，state_pressed，state_selected，state_focused，state_enabled 等几个状态：
android:state_pressed
Boolean. "true" if this item should be used when the object is pressed (such as when a button is touched/clicked); "false" if this item should be used in the default, non-pressed state.
如果是true，当被点击时显示该图片，如果是false没被按下时显示默认。
android:state_focused
Boolean. "true" if this item should be used when the object is focused (such as when a button is highlighted using the trackball/d-pad); "false" if this item should be used in the default, non-focused state.
true，获得焦点时显示；false，没获得焦点显示默认。
android:state_selected
Boolean. "true" if this item should be used when the object is selected (such as when a tab is opened); "false" if this item should be used when the object is not selected.
true，当被选择时显示该图片；false，当未被选择时显示该图片。
android:state_checkable
Boolean. "true" if this item should be used when the object is checkable; "false" if this item should be used when the object is not checkable. (Only useful if the object can transition between a checkable and non-checkable widget.)
true，当CheckBox能使用时显示该图片；false，当CheckBox不能使用时显示该图片。
android:state_checked
Boolean. "true" if this item should be used when the object is checked; "false" if it should be used when the object is un-checked.
true，当CheckBox选中时显示该图片；false，当CheckBox为选中时显示该图片。
android:state_enabled
Boolean. "true" if this item should be used when the object is enabled (capable of receiving touch/click events); "false" if it should be used when the object is disabled.
