方案一：继承自ImageView

package com.chy.widget;
import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.PaintFlagsDrawFilter;
import android.graphics.Path;
import android.graphics.Region;
import android.util.AttributeSet;
import android.widget.ImageView;
//有一个问题,当我把它放在列表项中, 然后列表上面有一个edittext用来filter, 结果发现该自定义imageview本该被edittext挡住, 结果却绘制在edittext之上
//初步判断是由canvas.clipPath(path, Region.Op.REPLACE);引起的,它把第一次不存在的部分也画了
//解决方案: REPLACE(覆盖) 改为 INTERSECT(交集)
public class CircleImageView extends ImageView { 
    private Paint paint = null;
    // 设置画布抗锯齿(毛边过滤)
    private PaintFlagsDrawFilter pfdf = null;
    private Path path = null;
    public CircleImageView(Context context) {
        super(context);
        init(context, null);
    }
    public CircleImageView(Context context, AttributeSet attrs) {
        super(context, attrs);
        init(context, attrs);
    }
    public CircleImageView(Context context, AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
        init(context, attrs);
    }
    // public CircleImageView(Context context, AttributeSet attrs, int
    // defStyleAttr, int defStyleRes) { 
    // super(context, attrs, defStyleAttr, defStyleRes);
    // init(context, attrs);
    // }
    private void init(Context context, AttributeSet attrs) {
        paint = new Paint();
        // 透明度: 00%=FF（不透明） 100%=00（透明）
        paint.setColor(Color.WHITE);
        // paint.setColor(Color.parseColor("ffffffff"));
        paint.setStyle(Paint.Style.STROKE);
        // 解决图片拉伸后出现锯齿的两种办法: 1.画笔上设置抗锯齿 2.画布上设置抗锯齿
        // http://labs.easymobi.cn/?p=3819
        paint.setFlags(Paint.ANTI_ALIAS_FLAG);
        paint.setAntiAlias(true);
        int clearBits = 0;
        int setBits = Paint.ANTI_ALIAS_FLAG | Paint.FILTER_BITMAP_FLAG;
        pfdf = new PaintFlagsDrawFilter(clearBits, setBits);
        //由于imageview有默认底色,如黑色,设置背景为透明是为了第一次setImageBitmap时不显示圆以外方型的默认背景色
        //但是这样在中兴nubia手机上还会首先显示正方形黑色背景,然后才变圆(解决办法,先裁成圆再setImageBitmap)
        setBackgroundColor(context.getResources().getColor(android.R.color.transparent));
    }
    @Override
    protected void onDraw(Canvas canvas) {
        int width = getWidth();
        int height = getHeight();
        // CCW: CounterClockwise(逆时针)
        // CW: Clockwise(顺时针)
        if (path == null) {
            path = new Path();
            path.addCircle(width / 2f, height / 2f, Math.min(width / 2f, height / 2f), Path.Direction.CCW);
            path.close();
        }
// canvas.drawCircle(width / 2f, height / 2f, Math.min(width / 2f, height / 2f), paint);
        // super.onDraw里面也可能有多个canvas.save
        int saveCount = canvas.save();
        canvas.setDrawFilter(pfdf);
        // Region.Op.REPLACE 是显示第二次的
// canvas.clipPath(path, Region.Op.REPLACE);
        canvas.clipPath(path, Region.Op.INTERSECT);
        super.onDraw(canvas);
        canvas.restoreToCount(saveCount);
    }
}

方案二：继承自View

package com.chy.widget;
import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Matrix;
import android.graphics.Paint;
import android.graphics.PaintFlagsDrawFilter;
import android.graphics.PorterDuff;
import android.graphics.PorterDuffXfermode;
import android.graphics.RectF;
import android.util.AttributeSet;
import android.view.View;
import android.widget.ImageView.ScaleType;
public class CircleView extends View { 
    private Paint paint = null;
    private PaintFlagsDrawFilter pfdf = null;
    // 在已有的图像上绘图将会在其上面添加一层新的形状, 设置这两个形状的显示方式
    private PorterDuffXfermode xfermode = null;
    private RectF rectf = null;
    private Bitmap bitmap = null;
    private Bitmap destBmp = null;
    private Matrix matrix = null;
    private ScaleType scaleType = ScaleType.CENTER_CROP;
    public CircleView(Context context) {
        super(context);
        init(context, null);
    }
    public CircleView(Context context, AttributeSet attrs) {
        super(context, attrs);
        init(context, attrs);
    }
    public CircleView(Context context, AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
        init(context, attrs);
    }
    // public CircleView(Context context, AttributeSet attrs, int defStyleAttr,
    // int defStyleRes) { 
    // super(context, attrs, defStyleAttr, defStyleRes);
    // init(context, attrs);
    // }
    private void init(Context context, AttributeSet attrs) {
        try {
            if (android.os.Build.VERSION.SDK_INT >= 11) {
                setLayerType(LAYER_TYPE_SOFTWARE, null);
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
        paint = new Paint();
        paint.setStyle(Paint.Style.FILL);
        paint.setColor(Color.WHITE);
        // 透明度: 00%=FF（不透明） 100%=00（透明）
        // paint.setColor(Color.parseColor("#ffffffff"));
        // 解决图片拉伸后出现锯齿的两种办法: 1.画笔上设置抗锯齿 2.画布上设置抗锯齿
        paint.setFlags(Paint.ANTI_ALIAS_FLAG);
        paint.setAntiAlias(true);
        int clearBits = 0;
        int setBits = Paint.ANTI_ALIAS_FLAG | Paint.FILTER_BITMAP_FLAG;
        pfdf = new PaintFlagsDrawFilter(clearBits, setBits);
        // PorterDuff.Mode.MULTIPLY只显示重叠部分
        xfermode = new PorterDuffXfermode(PorterDuff.Mode.MULTIPLY);
        matrix = new Matrix();
    }
    public void setImageResource(int resId) {
        Bitmap bmp = BitmapFactory.decodeResource(getResources(), resId);
        setBitmap(bmp);
    }
    public void setBitmap(Bitmap bmp) {
        this.bitmap = bmp;
    }
    public void setScaleType(ScaleType scaleType) {
        this.scaleType = scaleType;
    }
    private void makeDestBmp(int width, int height) {
        destBmp = Bitmap.createBitmap(width, height, Bitmap.Config.ARGB_8888);
        rectf = new RectF(0, 0, width, height);
        Canvas canvas = new Canvas(destBmp);
        canvas.drawOval(rectf, paint);
    }
    @Override
    protected void onDraw(Canvas canvas) {
        if (bitmap == null) {
            return;
        }
        int width = getWidth();
        int height = getHeight();
        int bmpWidth = bitmap.getWidth();
        int bmpHeight = bitmap.getHeight();
        if (destBmp == null) {
            makeDestBmp(width, height);
        }
        // canvas.save();
        // 设置画布抗锯齿
        canvas.setDrawFilter(pfdf);
        canvas.drawBitmap(destBmp, 0, 0, paint);
        paint.setXfermode(xfermode);
        switch(scaleType) {
        case FIT_XY:
             canvas.drawBitmap(bitmap, null, rectf, paint);
            break;
        case CENTER_CROP:
        default:
            matrix.reset();
            float scale = Math.max((float) width / (float) bmpWidth, (float) height / (float) bmpHeight);
            // 默认绕原点进行缩放 matrix.postScale(scale, scale, 0, 0);
            matrix.postScale(scale, scale, 0, 0);
            matrix.postTranslate((width - bmpWidth * scale) / 2f, (height - bmpHeight * scale) / 2f);
            canvas.drawBitmap(bitmap, matrix, paint);
            break;
        }
        paint.setXfermode(null);
        // canvas.restore();
    }
}