居中:
android:layout_gravity="center_horizontal" 相对于父窗体居中
android:gravity="center_horizontal" 相对于控件居中
底部栏切换变颜色
<?xml version="1.0" encoding="utf-8"?>
<selector xmlns:android="http://schemas.android.com/apk/res/android">
//选中
<item android:state_checked="true"
android:state_enabled="true"
android:drawable="@mipmap/collide_select"></item>
//普通
<item android:drawable="@mipmap/collide_unselect"></item>
</selector>
May everyone be happy every day and everything go well!