所以，这就是我所做的.我创建了一个名为 BlackoutView 的自定义 UIView 子类，如下所示:

So, here’s what I did. I created a custom UIView subclass called BlackoutView, like so:

BlackoutView.h

#import <UIKit/UIKit.h>

@interface BlackoutView : UIView

@property (nonatomic, retain) UIColor *fillColor;
@property (nonatomic, retain) NSArray *framesToCutOut;

@end

BlackoutView.m

#import "BlackoutView.h"

@implementation BlackoutView

- (void)drawRect:(CGRect)rect
{
    [self.fillColor setFill];
    UIRectFill(rect);

    CGContextRef context = UIGraphicsGetCurrentContext();
    CGContextSetBlendMode(context, kCGBlendModeDestinationOut);

    for (NSValue *value in self.framesToCutOut) {
        CGRect pathRect = [value CGRectValue];
        UIBezierPath *path = [UIBezierPath bezierPathWithOvalInRect:pathRect];
        [path fill];
    }

    CGContextSetBlendMode(context, kCGBlendModeNormal);
}

@end

然后我像往常一样实例化它，并将属性设置为我想要使用的蒙版的颜色，以及要从蒙版中切出的帧:

I then instantiate it as normal, and set the properties to the colour of the mask I want to use, and the frames to be cut out of the mask:

[blackMask setFillColor:[UIColor colorWithWhite:0.0f alpha:0.8f]];
[blackMask setFramesToCutOut:@[[NSValue valueWithCGRect:buttonCircleA.frame],
                               [NSValue valueWithCGRect:buttonCircleB.frame]]];

这可以通过允许我切出除椭圆之外的其他形状来改进，但这对我的目的来说很好，以后很容易适应这样做.希望这对其他人有帮助！

This could be improved by allowing me to cut out other shapes besides ovals, but it’s fine for my purposes here and would be easily adapted to do so later. Hopefully this helps others!