Android 自定义Button按钮显示样式（正常、按下、获取焦点）
现在的用户对APP的外观看得很重要，如果APP内所有元件都用Android默认样式写，估计下面评论里就有一堆在骂UI丑的。今天学习自定义Button按钮样式。Button样式修改的是Button的背景(Background)属性。首先写一个定义Button样式的XML文件：
新建Android XML文件，类型选Drawable,根结点选selector,文件名就buton_style吧。
程序自动给我们刚刚建的文件里加了selector结点，我们只需要在selector结点里写上三种状态时显示的背景图片（按下、获取焦点，正常）。
代码如下：
<span style="border:0px; font-family:inherit; font-style:inherit; margin:0px; outline:0px; padding:0px; vertical-align:baseline; color:rgb(0,153,0)"><span style="border:0px; font-family:inherit; font-style:inherit; margin:0px; outline:0px; padding:0px; vertical-align:baseline; color:rgb(0,0,0)"><strong><?xml</strong></span> <span style="border:0px; font-family:inherit; font-style:inherit; margin:0px; outline:0px; padding:0px; vertical-align:baseline; color:rgb(0,0,102)">version</span>=<span style="border:0px; font-family:inherit; font-style:inherit; margin:0px; outline:0px; padding:0px; vertical-align:baseline; color:rgb(255,0,0)">"1.0"</span> <span style="border:0px; font-family:inherit; font-style:inherit; margin:0px; outline:0px; padding:0px; vertical-align:baseline; color:rgb(0,0,102)">encoding</span>=<span style="border:0px; font-family:inherit; font-style:inherit; margin:0px; outline:0px; padding:0px; vertical-align:baseline; color:rgb(255,0,0)">"utf-8"</span><span style="border:0px; font-family:inherit; font-style:inherit; margin:0px; outline:0px; padding:0px; vertical-align:baseline; color:rgb(0,0,0)"><strong>?></strong></span></span>
<span style="border:0px; font-family:inherit; font-style:inherit; margin:0px; outline:0px; padding:0px; vertical-align:baseline; color:rgb(0,153,0)"><span style="border:0px; font-family:inherit; font-style:inherit; margin:0px; outline:0px; padding:0px; vertical-align:baseline; color:rgb(0,0,0)"><strong><selector</strong></span> <span style="border:0px; font-family:inherit; font-style:inherit; margin:0px; outline:0px; padding:0px; vertical-align:baseline; color:rgb(0,0,102)">xmlns:android</span>=<span style="border:0px; font-family:inherit; font-style:inherit; margin:0px; outline:0px; padding:0px; vertical-align:baseline; color:rgb(255,0,0)">"http://schemas.android.com/apk/res/android"</span><span style="border:0px; font-family:inherit; font-style:inherit; margin:0px; outline:0px; padding:0px; vertical-align:baseline; color:rgb(0,0,0)"><strong>></strong></span></span>
<span style="border:0px; font-family:inherit; font-style:inherit; margin:0px; outline:0px; padding:0px; vertical-align:baseline; color:rgb(0,153,0)"><span style="border:0px; font-family:inherit; font-style:inherit; margin:0px; outline:0px; padding:0px; vertical-align:baseline; color:rgb(0,0,0)"><strong><item</strong></span> <span style="border:0px; font-family:inherit; font-style:inherit; margin:0px; outline:0px; padding:0px; vertical-align:baseline; color:rgb(0,0,102)">android:state_pressed</span>=<span style="border:0px; font-family:inherit; font-style:inherit; margin:0px; outline:0px; padding:0px; vertical-align:baseline; color:rgb(255,0,0)">"true"</span> <span style="border:0px; font-family:inherit; font-style:inherit; margin:0px; outline:0px; padding:0px; vertical-align:baseline; color:rgb(0,0,102)">android:drawable</span>=<span style="border:0px; font-family:inherit; font-style:inherit; margin:0px; outline:0px; padding:0px; vertical-align:baseline; color:rgb(255,0,0)">"@drawable/play_press"</span> <span style="border:0px; font-family:inherit; font-style:inherit; margin:0px; outline:0px; padding:0px; vertical-align:baseline; color:rgb(0,0,0)"><strong>/></strong></span></span>
<span style="border:0px; font-family:inherit; font-style:inherit; margin:0px; outline:0px; padding:0px; vertical-align:baseline; color:rgb(0,153,0)"><span style="border:0px; font-family:inherit; font-style:inherit; margin:0px; outline:0px; padding:0px; vertical-align:baseline; color:rgb(0,0,0)"><strong><item</strong></span> <span style="border:0px; font-family:inherit; font-style:inherit; margin:0px; outline:0px; padding:0px; vertical-align:baseline; color:rgb(0,0,102)">android:state_focused</span>=<span style="border:0px; font-family:inherit; font-style:inherit; margin:0px; outline:0px; padding:0px; vertical-align:baseline; color:rgb(255,0,0)">"true"</span> <span style="border:0px; font-family:inherit; font-style:inherit; margin:0px; outline:0px; padding:0px; vertical-align:baseline; color:rgb(0,0,102)">android:drawable</span>=<span style="border:0px; font-family:inherit; font-style:inherit; margin:0px; outline:0px; padding:0px; vertical-align:baseline; color:rgb(255,0,0)">"@drawable/play_press"</span> <span style="border:0px; font-family:inherit; font-style:inherit; margin:0px; outline:0px; padding:0px; vertical-align:baseline; color:rgb(0,0,0)"><strong>/></strong></span></span>
<span style="border:0px; font-family:inherit; font-style:inherit; margin:0px; outline:0px; padding:0px; vertical-align:baseline; color:rgb(0,153,0)"><span style="border:0px; font-family:inherit; font-style:inherit; margin:0px; outline:0px; padding:0px; vertical-align:baseline; color:rgb(0,0,0)"><strong><item</strong></span> <span style="border:0px; font-family:inherit; font-style:inherit; margin:0px; outline:0px; padding:0px; vertical-align:baseline; color:rgb(0,0,102)">android:drawable</span>=<span style="border:0px; font-family:inherit; font-style:inherit; margin:0px; outline:0px; padding:0px; vertical-align:baseline; color:rgb(255,0,0)">"@drawable/play"</span> <span style="border:0px; font-family:inherit; font-style:inherit; margin:0px; outline:0px; padding:0px; vertical-align:baseline; color:rgb(0,0,0)"><strong>/></strong></span></span>
<span style="border:0px; font-family:inherit; font-style:inherit; margin:0px; outline:0px; padding:0px; vertical-align:baseline; color:rgb(0,153,0)"><span style="border:0px; font-family:inherit; font-style:inherit; margin:0px; outline:0px; padding:0px; vertical-align:baseline; color:rgb(0,0,0)"><strong></selector<span style="border:0px; font-family:inherit; font-style:inherit; margin:0px; outline:0px; padding:0px; vertical-align:baseline">></span></strong></span></span>
我这里获取焦点跟点击时显示的是同一张图片，必须严格照上面的顺序写，不可倒。
接下来只要在布局时写Button控件时应用到Button的Background属性即可。
<span style="border:0px; font-family:inherit; font-style:inherit; margin:0px; outline:0px; padding:0px; vertical-align:baseline; color:rgb(0,153,0)"><span style="border:0px; font-family:inherit; font-style:inherit; margin:0px; outline:0px; padding:0px; vertical-align:baseline; color:rgb(0,0,0)"><strong><Button</strong></span> <span style="border补充：移动开发 , Android ,
