1 shape

<?xml version="1.0" encoding="utf-8"?>
<shape android:shape="rectangle|oval|line|ring"
    xmlns:android="http://schemas.android.com/apk/res/android">
 <corners
     android:radius=""
     android:topLeftRadius=""
     android:topRightRadius=""
     android:bottomLeftRadius=""
     android:bottomRightRadius=""
     />
    <gradient
        android:angle=""
        android:centerX=""
        android:centerY=""
        android:startColor=""
        android:centerColor=""
        android:endColor=""
        android:gradientRadius=""
        android:type="linear|radial|sweep"
        android:useLevel="true|false"
        />
    <padding
        android:top=""
        android:left=""
        android:right=""
        android:bottom=""
       />
    <size
        android:width=""
        android:height=""
        />
    <solid
        android:color=""
        />
    <stroke
        android:width=""
        android:color=""
        android:dashWith=""
        android:dashCap=""
        />
</shape>

2 LayerDrawable用于progressDrawable

progress——drawable
<?xml version="1.0" encoding="utf-8"?>
<layer-list xmlns:android="http://schemas.android.com/apk/res/android">
    <item android:id="@android:id/background">
        <shape>
            <corners android:radius="90dp" />
            <solid android:color="#ffffff"/>
        </shape>
    </item>
    <item android:id="@android:id/secondaryProgress">
        <clip>
            <shape>
                <corners android:radius="90dip" />
                <gradient
                    android:angle="270"
                    android:centerColor="#C6B7FF"
                    android:centerY="0.75"
                    android:endColor="#C3B2FF"
                    android:startColor="#B9A4FF" />
            </shape>
        </clip>
    </item>
    <item android:id="@android:id/progress">
        <clip>
        <shape>
            <corners android:radius="90dp" />
            <gradient
                android:angle="0"
                android:endColor="#df0024"
                android:startColor="#de4e2c" />
        </shape>
        </clip>
    </item>
</layer-list>
progressbar的背景，padding=2dp之内填充progressdrawable，外面形成2dp的的边框
<?xml version="1.0" encoding="utf-8"?>
<shape xmlns:android="http://schemas.android.com/apk/res/android" android:shape="rectangle">
  <solid android:color="@color/colorPrimaryDark"/>
    <corners android:radius="90dp"/>
    <solid android:color="#cecece"/>
    <padding
        android:bottom="2dp"
        android:top="2dp"
        android:left="2dp"
        android:right="2dp"
        />
</shape>

3 stateList也就是selector

4LevelListDrawable

<?xml version="1.0" encoding="utf-8"?>
<level-list xmlns:android="http://schemas.android.com/apk/res/android">
    <item android:drawable="@drawable/shape_gray" android:maxLevel="0" />
    <item android:drawable="@drawable/shape_login" android:maxLevel="1"/>
</level-list>
<?xml version="1.0" encoding="utf-8"?>
<level-list xmlns:android="http://schemas.android.com/apk/res/android">
    <item android:drawable="@drawable/collapse" android:maxLevel="0" />
    <item android:drawable="@drawable/expanded" android:maxLevel="1"/>
</level-list>

    <ImageView
        android:id="@+id/iv"
        android:layout_width="100dp"
        android:layout_height="100dp"
        android:layout_marginTop="100dp"
        android:background="@drawable/level_drawable_bg"
        android:src="@drawable/level_drawable"
        app:layout_constraintTop_toTopOf="parent" />


            iv.setImageLevel(level);//切换前景图
            LevelListDrawable levelListDrawable= (LevelListDrawable) iv.getBackground();
            levelListDrawable.setLevel(level);//切换背景图

4TransitionDrawable

<?xml version="1.0" encoding="utf-8"?>
<transition xmlns:android="http://schemas.android.com/apk/res/android">
    <item android:drawable="@drawable/shape_gray" />
    <item android:drawable="@drawable/shape_login" />
</transition>

 TransitionDrawable transitionDrawable = (TransitionDrawable) tv.getBackground();
            transitionDrawable.startTransition(1000);