我在我的代码中遇到了一些好奇的东西,并且想知道这个行为是否有直接的解释.鉴于以下声明：
if let tabBarController = topViewController as? UITabBarController {
for subcontroller in tabBarController.viewControllers! {
println(subcontroller.view)
if let subcontrollerView = subcontroller.view {
println(subcontrollerView)
println(subcontrollerView!)
if subcontrollerView!.window != nil && subcontroller.isViewLoaded() {
topViewController = subcontroller as? UIViewController
break;
}
}
}
}
据我所知,if-let语句应该为我解开条件 – 但这不是这里展示的行为.除非我再次打开可选项,否则我无法访问subcontrollerView的window属性. x-code控制台返回以下内容：
Optional(<UILayoutContainerView: 0x7fbccd44e7f0; frame = (0 0; 320 568); autoresize = W+H; gestureRecognizers = <NSArray: 0x7fbccacdde90>; layer = <CALayer: 0x7fbccd440e30>>) Optional(<UILayoutContainerView: 0x7fbccd44e7f0; frame = (0 0; 320 568); autoresize = W+H; gestureRecognizers = <NSArray: 0x7fbccacdde90>; layer = <CALayer: 0x7fbccd440e30>>) <UILayoutContainerView: 0x7fbccd44e7f0; frame = (0 0; 320 568); autoresize = W+H; gestureRecognizers = <NSArray: 0x7fbccacdde90>; layer = <CALayer: 0x7fbccd440e30>>
展开的可选和if-let常量是相同的.为什么？
解决方法
你的问题是AnyObject. (如果有疑问,你的问题总是AnyObject;它是一种应该尽可能避免的邪恶类型.唯一更糟的是AnyObject？)
问题是tabBarController.viewControllers返回[AnyObject] ?,可选的促销可能会导致事情横向发展.它可能会推广AnyObject？一个AnyObject ??然后变得困惑.这有点像编译器错误,但也只是AnyObject带来的疯狂.所以答案就是尽可能快地摆脱它.
而不是这个：
for subcontroller in tabBarController.viewControllers! {
你要这个：
if let viewControllers = tabBarController.viewControllers as? [UIViewController] {
for subcontroller in viewControllers {
所以完整的代码是这样的：
if let tabBarController = topViewController as? UITabBarController {
if let viewControllers = tabBarController.viewControllers as? [UIViewController] {
for subcontroller in viewControllers {
if let subcontrollerView = subcontroller.view {
if subcontrollerView.window != nil && subcontroller.isViewLoaded() {
topViewController = subcontroller
break;
} } } } }
但我们可以做得更好.首先,可选链接通常是管理多个if-lets的更好方法,当它不能正常工作时,我们可以使用Swift 1.2的新的multi-if-let语法来实现：
if let tabBarController = topViewController as? UITabBarController,viewControllers = tabBarController.viewControllers as? [UIViewController] {
for subcontroller in viewControllers {
if subcontroller.view?.window != nil && subcontroller.isViewLoaded() {
topViewController = subcontroller
break;
} } }
