iOS开发小结 - UINavigationBar设置shadowImage

我们先设置一下shadowImage为蓝色的图片，下面是代码：

let size = self.navigationController!.navigationBar.frame.size
UIGraphicsBeginImageContextWithOptions(size, false, UIScreen.mainScreen().scale)
var context = UIGraphicsGetCurrentContext()
UIColor.blueColor().setFill()
CGContextAddRect(UIGraphicsGetCurrentContext(), CGRectMake(0, 0, size.width, 2))
CGContextDrawPath(context, .Fill)
var image = UIGraphicsGetImageFromCurrentImageContext()
UIGraphicsEndImageContext()

self.navigationController?.navigationBar.shadowImage = image

设置完成后发现并没有效果，那是因为我们没有设置backgroundImage，我们先看一下apple官方对于这个属性的解释：

/* Default is nil. When non-nil, a custom shadow image to show instead of the default shadow image. For a custom shadow to be shown, a custom background image must also be set with -setBackgroundImage:forBarMetrics: (if the default background image is used, the default shadow image will be used).

大概意思就是像让shadowImage有作用，必须先设置backgroundImage，下面我们再实现一下一下代码，先设置backgroundImage为红色，然后再设置shadowImage：

let size = self.navigationController!.navigationBar.frame.size
UIGraphicsBeginImageContextWithOptions(size, false, UIScreen.mainScreen().scale)
var context = UIGraphicsGetCurrentContext()
UIColor.blueColor().setFill()
CGContextAddRect(UIGraphicsGetCurrentContext(), CGRectMake(0, 0, size.width, 2))
CGContextDrawPath(context, .Fill)
var image = UIGraphicsGetImageFromCurrentImageContext()
UIGraphicsEndImageContext()

self.navigationController?.navigationBar.shadowImage = image

UIGraphicsBeginImageContextWithOptions(CGSizeMake(size.width, size.width+20), false, UIScreen.mainScreen().scale)
context = UIGraphicsGetCurrentContext()
UIColor.redColor().setFill()
CGContextAddRect(UIGraphicsGetCurrentContext(), CGRectMake(0, 0, size.width, size.height+20))
CGContextDrawPath(context, .Fill)
image = UIGraphicsGetImageFromCurrentImageContext()
UIGraphicsEndImageContext()

self.navigationController?.navigationBar.setBackgroundImage(image, forBarMetrics: .Default)

这下发现起作用了，同样的想要影藏navBar下面的小黑线，只需要将设置shadowImage成一个空的UIImage就行了：

self.navigationController?.navigationBar.shadowImage = UIImage()
UIGraphicsBeginImageContextWithOptions(CGSizeMake(size.width, size.width+20), false, UIScreen.mainScreen().scale)
var context = UIGraphicsGetCurrentContext()
UIColor.whiteColor().setFill()
CGContextAddRect(UIGraphicsGetCurrentContext(), CGRectMake(0, 0, size.width, size.height+20))
CGContextDrawPath(context, .Fill)
var image = UIGraphicsGetImageFromCurrentImageContext()
UIGraphicsEndImageContext()

self.navigationController?.navigationBar.setBackgroundImage(image, forBarMetrics: .Default)