Android开发笔记之:在ImageView上绘制圆环的实现方法

<SPAN xmlns="http://www.w3.org/1999/xhtml">package yan.guoqi.rectphoto;
import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.Paint.Style;
import android.graphics.RectF;
import android.util.AttributeSet;
import android.widget.ImageView;
public class DrawImageView extends ImageView {
 private final Paint paint;
 private final Context context;&nbsp;
 public DrawImageView(Context context, AttributeSet attrs) {
  super(context, attrs);
  // TODO Auto-generated constructor stub
  this.context = context;
  this.paint = new Paint();
  this.paint.setAntiAlias(true); //消除锯齿
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; this.paint.setStyle(Style.STROKE);  //绘制空心圆或 空心矩形
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; }
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; @Override
 protected void onDraw(Canvas canvas) {
  // TODO Auto-generated method stub
  int center = getWidth()/2;
  int innerCircle = dip2px(context, 83); //内圆半径
  int ringWidth = dip2px(context, 10);   //圆环宽度

  // 第一种方法绘制圆环
  //绘制内圆
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; this.paint.setARGB(255, 138, 43, 226);
  this.paint.setStrokeWidth(2);
  canvas.drawCircle(center, center, innerCircle, this.paint);&nbsp;  

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; //绘制圆环
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; this.paint.setARGB(255, 138, 43, 226);
  this.paint.setStrokeWidth(ringWidth);
  canvas.drawCircle(center, center, innerCircle + 1 +ringWidth/2, this.paint);&nbsp;  

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; //绘制外圆&nbsp;
  this.paint.setARGB(255, 138, 43, 226);
  this.paint.setStrokeWidth(2);
  canvas.drawCircle(center, center, innerCircle + ringWidth, this.paint);&nbsp;&nbsp;  

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; super.onDraw(canvas);

 }
 /* 根据手机的分辨率从 dp 的单位 转成为 px(像素) */ 
 public static int dip2px(Context context, float dpValue) { 
  final float scale = context.getResources().getDisplayMetrics().density; 
  return (int) (dpValue * scale + 0.5f); 
 }&nbsp;
}
</SPAN>