在XML中显示圆

<!-- res/drawable/circle.xml -->
<shape xmlns:android="http://schemas.android.com/apk/res/android"
    android:shape="oval">
    <solid android:color="#FF0000"/> <!-- 圆的颜色 -->
    <size
        android:width="100dp"
        android:height="100dp"/> <!-- 圆的直径 -->
</shape>

<!-- res/layout/activity_main.xml -->
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <View
        android:id="@+id/circleView"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:background="@drawable/circle"/>
</RelativeLayout>