Android编程绘制圆形图片的方法

package com.rong.activity;
import com.rong.test.R;
import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.Bitmap.Config;
import android.graphics.BitmapFactory;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.PorterDuff;
import android.graphics.PorterDuffXfermode;
import android.util.AttributeSet;
import android.widget.ImageView;
/**
 * 利用Xfermode制作一个圆形图片
 * 
 * @author 徐荣
 *
 */
public class RoundView extends ImageView {
  /**
   * 画笔
   */
  private Paint mPaint;
  /**
   * 原型图
   */
  private Bitmap src;
  /**
   * 遮罩层
   */
  private Bitmap mask;
  public RoundView(Context context, AttributeSet attrs) {
    super(context, attrs);
    // 初始化画笔
    mPaint = new Paint();
    mPaint.setAntiAlias(true);
    // 拿到原型图
    src = BitmapFactory.decodeResource(getResources(), R.drawable.ml);
  }
  @Override
  protected void onSizeChanged(int w, int h, int oldw, int oldh) {
    super.onSizeChanged(w, h, oldw, oldh);
    // 图片的遮罩，为什么要在这里面初始化遮罩层呢？因为在这个方法里Width()和Height()才被初始化了
    mask = Bitmap.createBitmap(getMeasuredWidth(), getMeasuredHeight(), Config.ARGB_4444);
  }
  @Override
  protected void onDraw(Canvas canvas) {
    super.onDraw(canvas);
    // 设置画布的颜色为透明
    canvas.drawColor(Color.TRANSPARENT);
    // 划出你要显示的圆
    Canvas cc = new Canvas(mask);
    cc.drawCircle(getMeasuredWidth() / 2, getMeasuredHeight() / 2, getMeasuredHeight() / 2, mPaint);
    // 这个方法相当于PS新建图层，下面你要做的事就在这个图层上操作
    canvas.saveLayer(0, 0, getMeasuredWidth(), getMeasuredHeight(), null, Canvas.ALL_SAVE_FLAG);
    // 先绘制遮罩层
    canvas.drawBitmap(mask, 0, 0, mPaint);
    // 设置混合模式
    mPaint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.SRC_IN));
    // 再绘制src源图
    canvas.drawBitmap(src, 0, 0, mPaint);
    // 还原混合模式
    mPaint.setXfermode(null);
    // 还原画布，相当于Ps的合并图层
    canvas.restore();
  }
}

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
  android:layout_width="match_parent"
  android:layout_height="match_parent"
  android:background="#ffffff"
  android:orientation="vertical" >
  <com.rong.activity.RoundView
    android:layout_width="160dp"
    android:layout_height="160dp"
    android:layout_centerInParent="true" />
</RelativeLayout>