适配器backward.xml
<?xml version="1.0" encoding="utf-8"?>
<selector xmlns:android="http://schemas.android.com/apk/res/android" >
<item
android:state_pressed="true"
android:drawable="@drawable/bottom_bar_icon_backward_un"
></item>
<item
android:drawable="@drawable/bottom_bar_icon_backward_focus"
></item>
</selector>
main.xml布局文件
<ImageView
android:id="@+id/backward"
android:layout_width="wrap_content"
android:layout_height="40dp"
android:src="@drawable/backward"
android:paddingTop="8dp"
android:paddingBottom="8dp"
android:layout_weight="0.25"
android:clickable="true" //必须设置，才会有点击的效果
/>