Iphone 将阴影添加到CAShapeLayer，以便内部保持透明

我想给路径添加一个光晕效果，比如有焦点的（OSX）界面元素周围的蓝色光晕

我使用了一个带有（矩形）路径的CAShapeLayer：

最后，这给了我一个透明的UIView，周围有一个边框。（在我的具体案例中，它是一条带有附加动画的虚线，但这对于这个特定问题并不重要）

我使用了CALayer的阴影属性，但它们将始终填充整个层

self.borderLayer.shadowPath = self.borderLayer.path;
self.borderLayer.shouldRasterize = YES;

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我想要的是，只有UIView周围的线条会投射阴影，这样UIView的内部仍然是透明的。

我在看到我想要的阴影而不是辉光的内部时遇到了类似的问题。我用两个Calayer解决了这个问题。一个，在代码中，“_bg”作为背景（在我的例子中是黑色，不透明度为0.55）和白色边框。代码“_shadow”中的另一层具有清晰的背景并添加了辉光效果_bg是阴影层的子视图。以下是相关代码：

_bg = [CALayer layer];
_shadow = [CALayer layer];

[self.layer insertSublayer:_shadow atIndex:0];
[_shadow addSublayer:_bg];

_bg.frame = self.bounds;
_bg.backgroundColor = [UIColor colorWithRed:0.0 green:0.0 blue:0.0 alpha:.55].CGColor;
_bg.cornerRadius=20.0;
_bg.borderColor=[UIColor whiteColor].CGColor;
_bg.borderWidth=2.0;

_shadow.frame=self.bounds;
_shadow.masksToBounds=NO;
_shadow.backgroundColor = [UIColor clearColor].CGColor;
_shadow.cornerRadius=3.0;
_shadow.shadowRadius=3.0;
_shadow.shadowColor=[UIColor whiteColor].CGColor;
_shadow.shadowOpacity=0.6;
_shadow.shadowOffset=CGSizeMake(0.0, 0.0);

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您可以尝试以下方法：

    //background layer of the shadow layer
    contentViewBackgroundLayer = [CALayer layer];
    contentViewBackgroundLayer.frame = contentView.bounds;
    contentViewBackgroundLayer.backgroundColor = someColor.CGColor;
    //shadow layer
    contentViewShadowLayer = [CALayer layer];
    [contentViewShadowLayer addSublayer:contentViewBackgroundLayer];
    contentViewShadowLayer.backgroundColor = [UIColor clearColor].CGColor;
    //shadowRadius
    contentViewShadowLayer.shadowRadius = 10.0;
    contentViewShadowLayer.shadowColor = [UIColor blackColor].CGColor;
    contentViewShadowLayer.shadowOpacity = 0.5;
    contentViewShadowLayer.shadowOffset = CGSizeMake(0.0, 0.0);
    //Important!!!!  add mask to shadowLayer
    contentViewBackgroundLayer.frame = contentView.bounds;
    contentViewShadowLayer.frame = contentView.bounds;
    CGRect rect = CGRectMake(contentViewShadowLayer.bounds.origin.x - 20, contentViewShadowLayer.bounds.origin.y - 20, contentViewShadowLayer.bounds.size.width + 40, contentViewShadowLayer.bounds.size.height + 40);
    UIBezierPath *path = [UIBezierPath bezierPathWithRect:rect];
    [path appendPath:[UIBezierPath bezierPathWithRect:CGRectMake(0, 0, contentView.bounds.size.width, contentView.bounds.size.height)]];
    //a rectangle which is transparent surrounded by a bigger rectangle
    CAShapeLayer *shapeLayer = [CAShapeLayer layer];
    shapeLayer.fillRule = kCAFillRuleEvenOdd;
    shapeLayer.path = [path CGPath];
    contentViewShadowLayer.mask = shapeLayer;
    [contentView.layer insertSublayer:contentViewShadowLayer atIndex:0];

    //background layer of the shadow layer
    contentViewBackgroundLayer = [CALayer layer];
    contentViewBackgroundLayer.frame = contentView.bounds;
    contentViewBackgroundLayer.backgroundColor = someColor.CGColor;
    //shadow layer
    contentViewShadowLayer = [CALayer layer];
    [contentViewShadowLayer addSublayer:contentViewBackgroundLayer];
    contentViewShadowLayer.backgroundColor = [UIColor clearColor].CGColor;
    //shadowRadius
    contentViewShadowLayer.shadowRadius = 10.0;
    contentViewShadowLayer.shadowColor = [UIColor blackColor].CGColor;
    contentViewShadowLayer.shadowOpacity = 0.5;
    contentViewShadowLayer.shadowOffset = CGSizeMake(0.0, 0.0);
    //Important!!!!  add mask to shadowLayer
    contentViewBackgroundLayer.frame = contentView.bounds;
    contentViewShadowLayer.frame = contentView.bounds;
    CGRect rect = CGRectMake(contentViewShadowLayer.bounds.origin.x - 20, contentViewShadowLayer.bounds.origin.y - 20, contentViewShadowLayer.bounds.size.width + 40, contentViewShadowLayer.bounds.size.height + 40);
    UIBezierPath *path = [UIBezierPath bezierPathWithRect:rect];
    [path appendPath:[UIBezierPath bezierPathWithRect:CGRectMake(0, 0, contentView.bounds.size.width, contentView.bounds.size.height)]];
    //a rectangle which is transparent surrounded by a bigger rectangle
    CAShapeLayer *shapeLayer = [CAShapeLayer layer];
    shapeLayer.fillRule = kCAFillRuleEvenOdd;
    shapeLayer.path = [path CGPath];
    contentViewShadowLayer.mask = shapeLayer;
    [contentView.layer insertSublayer:contentViewShadowLayer atIndex:0];