<selector xmlns:android="http://schemas.android.com/apk/res/android" xmlns:app="http://schemas.android.com/apk/res-auto">
<!--折叠状态下的阴影 android:valueTo="5dp"控制阴影大小-->
<item app:state_collapsed="true">
android:propertyName="elevation"
android:valueTo="0dp"
android:valueType="floatType" />
<!--展开状态下的阴影-->
<item app:state_collapsed="false">
android:propertyName="elevation"
android:valueTo="0dp"
android:valueType="floatType" />
</selector>
<com.google.android.material.appbar.AppBarLayout
android:id="@+id/app_bar_layout"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:visibility="visible"
android:stateListAnimator="@drawable/appbar_elevation">
