Android imageview显示圆形图片

public static Bitmap toRoundCorner(Bitmap bitmap, float ratio) {
        System.out.println("图片是否变成圆形模式了+++++++++++++");
        Bitmap output = Bitmap.createBitmap(bitmap.getWidth(),
                bitmap.getHeight(), Bitmap.Config.ARGB_8888);
        Canvas canvas = new Canvas(output);

        final Paint paint = new Paint();
        final Rect rect = new Rect(0, 0, bitmap.getWidth(), bitmap.getHeight());
        final RectF rectF = new RectF(rect);

        paint.setAntiAlias(true);
        canvas.drawARGB(0, 0, 0, 0);
        canvas.drawRoundRect(rectF, bitmap.getWidth() / ratio,
                bitmap.getHeight() / ratio, paint);

        paint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.SRC_IN));
        canvas.drawBitmap(bitmap, rect, rect, paint);
        System.out.println("pixels+++++++" + String.valueOf(ratio));

        return output;

    }