Android空心圓及層疊效果實現代碼

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);
//  得到屏幕寬高
  float wi = canvas.getWidth() / 2;
  float he = canvas.getHeight() / 2;
//  創建第一個畫筆
  Paint pa = new Paint();
//  上色
  pa.setColor(Color.GREEN);
//  顯示圓邊
  pa.setAntiAlias(true);
//  設置空心圓環
  pa.setStyle(Paint.Style.STROKE);
//  設置圓環寬度
  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);
//  畫什么圓
  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>