如何把图片UIImageView某个区域变成透明

UIImageView *imageView = [[UIImageView alloc] initWithFrame:CGRectMake(0, 64, SIZE.width, SIZE.height)];

// imageView.alpha = 0.8;

[imageView setBackgroundColor:[UIColor grayColor]];

UIBezierPath *maskPath = [UIBezierPath bezierPathWithRect:imageView.bounds];

UIBezierPath *holePath = [UIBezierPath bezierPathWithRect:CGRectInset(CGRectMake(50, 100, SIZE.width-100, SIZE.width-100), 0, 0)];//
[maskPath appendPath:holePath];

CAShapeLayer *mask = [CAShapeLayer layer];
[mask setFillRule:kCAFillRuleEvenOdd];
mask.path = maskPath.CGPath;

[imageView.layer setMask:mask];

[self.view addSubview:imageView];