Android自定义View画圆功能

<?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.bwie.test.xuejian1508a20170928.MainActivity"  
 
 <com.bwie.test.xuejian1508a20170928.ViView 
 android:layout_width="match_parent" 
 android:layout_height="match_parent" 
  /  
</RelativeLayout 

public class ViView extends View{ 
 Paint paint; 
 Context context; 
 //构造方法 
 public ViView(Context context) { 
 super(context); 
 } 
 
 public ViView(Context context, AttributeSet attrs) { 
 super(context, attrs); 
 } 
 
 public ViView(Context context, AttributeSet attrs, int defStyleAttr) { 
 super(context, attrs, defStyleAttr); 
 } 
 
 public ViView(Context context, AttributeSet attrs, int defStyleAttr, int defStyleRes) { 
 super(context, attrs, defStyleAttr, defStyleRes); 
 this.context=context; 
 } 
 
 @Override 
 protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) { 
 super.onMeasure(widthMeasureSpec, heightMeasureSpec); 
 } 
 
 @Override 
 protected void onLayout(boolean changed, int left, int top, int right, int bottom) { 
 super.onLayout(changed, left, top, right, bottom); 
 
 } 
 
 /*绘图*/ 
 @Override 
 protected void onDraw(Canvas canvas) { 
 super.onDraw(canvas); 
 //得到屏幕宽高 
 int width = getWidth(); 
 int radius = width - 450/2; 
 int height = getHeight(); 
// 创建画笔 
 Paint paint1 = new Paint(); 
 Paint paint2 = new Paint(); 
 Paint paint3= new Paint(); 
// 消除锯齿 
 paint1.setAntiAlias(true); 
 paint2.setAntiAlias(true); 
 paint3.setAntiAlias(true); 
 //画笔颜色 
 paint1.setColor(Color.RED); 
 paint2.setColor(Color.WHITE); 
 paint3.setColor(Color.BLUE); 
// 画圆。确定位置 
// canvas.drawRect(100,100,width/2,height/2,paint1); 
// canvas.drawCircle(100,100,100,paint1); 
// canvas.drawCircle(250,250,200,paint2); 
// canvas.drawCircle(500,500,300,paint3); 
 //设置圆环形状和大小 
 RectF oval = new RectF(width-radius,width-radius,width+radius,width+radius); 
 paint1.setStrokeWidth(450); 
 canvas.drawArc(oval,-90,90,false,paint1); 
 
 canvas.drawCircle(width/2,height/2,450,paint1); 
 canvas.drawCircle(width/2,height/2,300,paint2); 
 canvas.drawCircle(width/2,height/2,200,paint3); 
 } 
 
 @Override 
 public boolean onTouchEvent(MotionEvent event) { 
 return super.onTouchEvent(event); 
 } 
}