绘制圆

在drawable绘制shape

<?xml version="1.0" encoding="utf-8"?>
<shape xmlns:android="http://schemas.android.com/apk/res/android">

    <stroke
        android:width="1dp"
        android:color="#f00ff0"     />
        <corners
            android:radius="15dp"
            />
<solid
    android:color="@color/colorAccent"
    />
</shape>

绘制圆

<?xml version="1.0" encoding="utf-8"?>
<shape
    android:shape="oval"
    xmlns:android="http://schemas.android.com/apk/res/android">
<stroke
    android:width="1dp"
    android:color="#f00ff0"

    />
    <size
        android:width="20dp"
        android:height="20dp"
        />
    <gradient
        android:startColor="#00f"
        android:centerColor="#f0f"
        android:endColor="#0ff"
        />
</shape>