ios - 如何在此定界图层中添加边框？

我有一张图片，上面使用图层和遮罩定界了透明矩形。
我希望此透明矩形为红色边框。但是我可以找到一种方法来实现这一目标：

这是我所做的：



我的ViewController具有darkenedView属性。

- (void)loadView {
    UIView *const rootView = [[UIView alloc] initWithFrame:CGRectMake(0, 0, 50, 50)];
    rootView.backgroundColor = [UIColor whiteColor];
    self.view = rootView;
    [self addContentSubviews];
}

- (void)addContentSubviews {
    UIImageView *const imageView = [[UIImageView alloc] initWithImage:[UIImage imageNamed:@"DSC_0823.jpg"]];
    imageView.contentMode = UIViewContentModeScaleAspectFill;
    imageView.frame = self.view.bounds;
    imageView.autoresizingMask = UIViewAutoresizingFlexibleHeight | UIViewAutoresizingFlexibleWidth;
    [self.view addSubview:imageView];
}

- (void)viewDidLoad {
    [super viewDidLoad];
    [self addDarkenedSubview];
}

- (void)viewDidLayoutSubviews {
    CGRect const bounds = self.view.bounds;
    darkenedView.center = CGPointMake(CGRectGetMidX(bounds), 0);
}

- (void)addDarkenedSubview {
    darkenedView = [[UIView alloc] initWithFrame:CGRectMake(10, 30, 400, 1200)];
    darkenedView.backgroundColor = [UIColor colorWithWhite:0.0 alpha:0.6];
    darkenedView.autoresizingMask = 0;
    [self.view addSubview:darkenedView];
    [self addMaskToDarkenedView];
}

- (void)addMaskToDarkenedView {
    CGRect bounds = darkenedView.bounds;
    CAShapeLayer *maskLayer = [CAShapeLayer layer];
    maskLayer.frame = bounds;

    CGRect const myRect = CGRectMake(CGRectGetMidX(bounds) - 100,
        CGRectGetMidY(bounds) + 100,
        200, 200);
    UIBezierPath *path = [UIBezierPath bezierPathWithRect:myRect];
    [path appendPath:[UIBezierPath bezierPathWithRect:bounds]];
    maskLayer.path = path.CGPath;
    maskLayer.fillRule = kCAFillRuleEvenOdd;
    darkenedView.layer.mask = maskLayer;

}

我尝试过没有成功：

maskLayer.strokeColor = [UIColor redColor].CGColor;
maskLayer.lineWidth = 3.0f;

最佳答案

下面是示例代码，而不是给maskLayer对象添加笔触，而是创建CAShapeLayer和addSublayer到darkenedView视图。

CAShapeLayer *shape = [CAShapeLayer layer];
shape.frame = darkenedView.bounds;
shape.path = path.CGPath;
shape.lineWidth = 3.0f;
shape.strokeColor = [UIColor redColor].CGColor;
shape.fillColor = [UIColor clearColor].CGColor;
[darkenedView.layer addSublayer:shape];