直接上代码： 看注解

@SuppressLint("AppCompatCustomView")

public class MyTestImageView extends ImageView {

    private float width;

    private float height;

    private float radius;

    private Paint paint;

    private Matrix matrix;

    public MyTestImageView(Context context) {

        this(context, null);

    }

    public MyTestImageView(Context context, @Nullable AttributeSet attrs) {

        super(context, attrs);

        paint = new Paint();

        paint.setAntiAlias(true);

        matrix = new Matrix();

    }

    @Override

    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {

        super.onMeasure(widthMeasureSpec, heightMeasureSpec);

        width = getMeasuredWidth();

        height = getMeasuredHeight();

        radius = DensityUtils.dpForPx(3);

    }

    @SuppressLint("DrawAllocation")

    @Override

    protected void onDraw(Canvas canvas) {

// 第三种就直接用 PorterDuffXfermode 去交集 DST_IN 来得倒 交集的后 gif 图片展示

//加这个是为了隔离图层，避免黑色的底边

       int layerID = canvas.saveLayer(0, 0, width, height, paint, Canvas.ALL_SAVE_FLAG);        @SuppressLint("DrawAllocation") RectF f1 = new RectF(0.0f, 0.0f, width, height);

        @SuppressLint("DrawAllocation") Path ra = new Path();

        ra.addRoundRect(f1, radius, radius, Path.Direction.CCW);

        paint.setColor(ContextCompat.getColor(this.getContext(), R.color.color_fff));

        //        canvas.clipPath(ra);//第一种 直接裁剪画布，根据实践有锯齿

        super.onDraw(canvas);

        paint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.DST_IN));

        canvas.drawPath(ra, paint);

        paint.setXfermode(null);

//回复图层

       canvas.restoreToCount(layerID);

// 第二种 给imageview 加相框 不过得适配画笔颜色和布局背景颜色一样。

//        Drawable drawable = getDrawable();

//        if (null != drawable) {

//            @SuppressLint("DrawAllocation")

//            RectF f = new RectF(0.0f, 0.0f, width, height);

//            @SuppressLint("DrawAllocation") Path now = new Path();

//            @SuppressLint("DrawAllocation") Path bg = new Path();

//            bg.addRect(f, Path.Direction.CCW);

//            now.addRoundRect(f, radius, radius, Path.Direction.CCW);

//            if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.KITKAT)

//                now.op(bg, now, Path.Op.DIFFERENCE);

//            canvas.drawPath(now, paint);

//        }

    }

}