空心圆及层叠效果

package com.bwei.test.zidingyiview2;

import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.util.AttributeSet;
import android.view.View;


public class MyView extends View {
    private Context mcontext;
    private Paint mpaint;

    public MyView(Context context) {
        super(context);
    }

    public MyView(Context context, AttributeSet attrs) {
        super(context, attrs);
    }

    public MyView(Context context, AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
        this.mcontext = context;
    }

    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
//        得到屏幕宽高
        float wi = canvas.getWidth() / 2;
        float he = canvas.getHeight() / 2;
//        创建第一个画笔
        Paint pa = new Paint();
//        上色
        pa.setColor(Color.GREEN);
//        显示圆边
        pa.setAntiAlias(true);
//        设置空心圆环
        pa.setStyle(Paint.Style.STROKE);
//        设置圆环宽度
        pa.setStrokeWidth(6);
        Paint pa2 = new Paint();
        pa2.setColor(Color.BLUE);
        pa2.setAntiAlias(true);
        Paint pa3 = new Paint();
        pa3.setColor(Color.BLACK);
        pa3.setAntiAlias(true);
//        画什么圆
        canvas.drawCircle(wi-85, he-85, 80, pa2);
        canvas.drawCircle(wi, he, 100, pa);
        canvas.drawCircle(wi+110, he+110, 120, pa3);
    }
}

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/activity_main"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context="com.bwei.test.zidingyiview2.MainActivity">

   <com.bwei.test.zidingyiview2.MyView
       android:layout_width="wrap_content"
       android:layout_height="wrap_content"/>
</RelativeLayout>