我们经常看到一些app中可以显示圆角图片，比如qq的联系人图标等等，实现圆角图片一种办法是直接使用圆角图片资源，当然如果没有圆角图片资源，我们也可以自己通过程序实现的，下面介绍一个自定义圆角ImageView的方法：

import android.content.Context;  
import android.content.res.TypedArray;  
import android.graphics.Bitmap;  
import android.graphics.Bitmap.Config;  
import android.graphics.Canvas;  
import android.graphics.Color;  
import android.graphics.Paint;  
import android.graphics.Path;  
import android.graphics.PorterDuff;  
import android.graphics.PorterDuffXfermode;  
import android.graphics.RectF;  
import android.util.AttributeSet;  
import android.widget.ImageView;  
  
public class RoundAngleImageView extends ImageView {  
    private int roundWidth = 13;  
    private int roundHeight = 13;  
  
    public RoundAngleImageView(Context context) {  
        super(context);  
        init(context, null);  
    }  
  
    public RoundAngleImageView(Context context, AttributeSet attrs, int defStyle) {  
        super(context, attrs, defStyle);  
        init(context, attrs);  
    }  
  
    public RoundAngleImageView(Context context, AttributeSet attrs) {  
        super(context, attrs);  
        init(context, attrs);  
    }  
  
    private void init(Context context, AttributeSet attrs) {  
        if (attrs != null) {  
            TypedArray a = context.obtainStyledAttributes(attrs,  
                    R.styleable.RoundAngleImageView);  
            roundWidth = a.getDimensionPixelSize(  
                    R.styleable.RoundAngleImageView_roundWidth, roundWidth);  
            roundHeight = a.getDimensionPixelSize(  
                    R.styleable.RoundAngleImageView_roundHeight, roundHeight);  
            a.recycle();  
        } else {  
            float density = context.getResources().getDisplayMetrics().density;  
            roundWidth = (int)(roundWidth * density);  
            roundHeight = (int)(roundHeight * density);  
        }  
    }  
  
    /** 重写draw() */  
    @Override  
    public void draw(Canvas canvas) {  
          
        //实例化一个和ImageView一样大小的bitmap  
        Bitmap bitmap = Bitmap.createBitmap(getWidth(), getHeight(),  
                Config.ARGB_8888);  
          
        //实例化一个canvas，这个canvas对应的内存为上面的bitmap  
        Canvas canvas2 = new Canvas(bitmap);  
        if (bitmap.isRecycled()) {  
            bitmap = Bitmap.createBitmap(getWidth(), getHeight(),  
                    Config.ARGB_8888);  
            canvas2 = new Canvas(bitmap);  
        }  
          
        //将imageView自己绘制到canvas2上，这个导致bitmap里面存放了imageView  
        super.draw(canvas2);  
          
        //利用canvas画一个圆角矩形，这个会修改bitmap的数据  
        drawRoundAngle(canvas2);  
          
        //将裁剪好的bitmap绘制到系统当前canvas上，这样裁剪好的imageview就能显示到屏幕上  
        Paint paint = new Paint();  
        paint.setXfermode(null);  
        canvas.drawBitmap(bitmap, 0, 0, paint);  
        bitmap.recycle();  
    }  
  
    public void setRoundWidth(int roundWidth, int roundHeight) {  
        this.roundWidth = roundWidth;  
        this.roundHeight = roundHeight;  
    }  
  
    private void drawRoundAngle(Canvas canvas)  
    {  
        Paint maskPaint = new Paint();  
        maskPaint.setAntiAlias(true);  
        maskPaint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.CLEAR));  
        Path maskPath = new Path();    
        maskPath.addRoundRect(new RectF(0.0F, 0.0F, getWidth(), getHeight()), roundWidth, roundHeight, Path.Direction.CW);  
          
        //这是设置了填充模式，非常关键  
        maskPath.setFillType(Path.FillType.INVERSE_WINDING);  
        canvas.drawPath(maskPath, maskPaint);  
    }  
}