Drawable的使用——LevelListDrawable

LevelListDrawable对应于标签，它同样表示一个Drawable集合，集合中每个Drawable都有一个等级(level)的概念。根据不通的等级，LevelListDrawable会显示对应的Drawable

<level-list xmlns:android="http://schemas.android.com/apk/res/android">
    <item
        android:drawable="@drawable/ic_sunny"
        android:maxLevel="10"
        android:minLevel="0" />
    <item
        android:drawable="@drawable/ic_night"
        android:maxLevel="20"
        android:minLevel="11" />
    <item
        android:drawable="@drawable/ic_cloudy"
        android:maxLevel="30"
        android:minLevel="21" />
level-list>

     var count = 0
        iv_level_list.setOnClickListener {
            count++
            when (count % 3) {
                0 -> iv_level_list.drawable.level = 5
                1 -> iv_level_list.drawable.level = 15
                2 -> iv_level_list.drawable.level = 25
            }
        }

效果如下：