只需使用

ShapeDrawable circle = new ShapeDrawable( new  OvalShape() );

您可以按如下方式使用VectorDrawable：

<?xml version="1.0" encoding="utf-8"?>
<vector xmlns:android="http://schemas.android.com/apk/res/android"
    android:width="200dp"
    android:height="200dp"
    android:viewportHeight="64"
    android:viewportWidth="64">

    <path
        android:fillColor="#ff00ff"
        android:pathData="M22,32
        A10,10 0 1,1 42,32
        A10,10 0 1,1 22,32 Z" />
</vector>

上述xml呈现为：

您可以创建自定义绘图来动态更改圆的颜色和半径

import android.graphics.Canvas;
import android.graphics.ColorFilter;
import android.graphics.Paint;
import android.graphics.PixelFormat;
import android.graphics.drawable.Drawable;

import androidx.annotation.NonNull;
import androidx.annotation.Nullable;

public class CircleDrawable extends Drawable {

    private Paint circlePaint;
    private int fillColor;
    private int strokeColor;
    private float radius;

    public CircleDrawable(int fillColor, int strokeColor, float radius) {
        this.fillColor = fillColor;
        this.strokeColor = strokeColor;
        this.radius = radius;
        circlePaint=new Paint(Paint.ANTI_ALIAS_FLAG);
    }

    @Override
    public void draw(@NonNull Canvas canvas) {
        int x=getBounds().centerX();
        int y=getBounds().centerY();
        //draw fill color circle
        circlePaint.setStyle(Paint.Style.FILL);
        circlePaint.setColor(fillColor);
        canvas.drawCircle(x,y,radius,circlePaint);
        // draw stroke circle
        circlePaint.setStyle(Paint.Style.STROKE);
        circlePaint.setColor(strokeColor);
        circlePaint.setStrokeWidth(5);
        canvas.drawCircle(x,y,radius,circlePaint);
    }

    @Override
    public void setAlpha(int alpha) {
        circlePaint.setAlpha(alpha);
    }

    @Override
    public void setColorFilter(@Nullable ColorFilter colorFilter) {
         circlePaint.setColorFilter(colorFilter);
    }

    @Override
    public int getOpacity() {
        return PixelFormat.TRANSLUCENT;
    }
}

从UI设置此项以获得圆形

imageView.setImageDrawable(new CircleDrawable(Color.RED,Color.YELLOW,100));

输出将是这样的

由于某种原因，我无法在ConstraintLayout中画一个圆圈，我只是无法使用上面的任何答案。

当你按下“Alt+7”时，一个简单的文本视图显示了文本，效果很好：

 <TextView
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:textColor="#0075bc"
            android:textSize="40dp"
            android:text="•"></TextView>

res/drawable/circle_shape.xml

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

        <shape android:shape="oval">
            <solid android:color="#e42828"/>
            <stroke android:color="#3b91d7" android:width="5dp"/>
            <!-- Set the same value for both width and height to get a circular shape -->
            <size android:width="250dp" android:height="250dp"/>
        </shape>
    </item>
</selector>

你可以尝试使用这个

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

<item>
    <shape
        android:innerRadius="0dp"
        android:shape="ring"
        android:thicknessRatio="2"
        android:useLevel="false" >
        <solid android:color="@color/button_blue_two" />
    </shape>
</item>

如果您将其用于文本视图，则不必担心宽度和高度纵横比