swift - 我可以在 UIViewController 中扩展 viewWillAppear 吗？

Question

我正在寻找一种方法来扩展 UIViewController 类的函数 viewWillAppear 的实现，以使其在每次调用此函数时打印所调用 View 的类名。

我知道不可能覆盖扩展中的函数，所以我想知道是否有任何方法可以做这样的事情。

Answer 1

好的，找到这个之后http://nshipster.com/swift-objc-runtime/我尝试了类似的东西并且可以达到预期的结果。

代码如下:

extension UIViewController {
public override class func initialize() {
    struct Static {
        static var token: dispatch_once_t = 0
    }

    // make sure this isn't a subclass
    if self !== UIViewController.self {
        return
    }

    dispatch_once(&Static.token) {
        let originalSelector = #selector(UIViewController.viewWillAppear(_:))
        let swizzledSelector = #selector(UIViewController.nsh_viewWillAppear(_:))

        let originalMethod = class_getInstanceMethod(self, originalSelector)
        let swizzledMethod = class_getInstanceMethod(self, swizzledSelector)

        let didAddMethod = class_addMethod(self, originalSelector, method_getImplementation(swizzledMethod), method_getTypeEncoding(swizzledMethod))

        if didAddMethod {
            class_replaceMethod(self, swizzledSelector, method_getImplementation(originalMethod), method_getTypeEncoding(originalMethod))
        } else {
            method_exchangeImplementations(originalMethod, swizzledMethod)
        }
    }
}

// MARK: - Method Swizzling

func nsh_viewWillAppear(animated: Bool) {
    self.nsh_viewWillAppear(animated)
    NSLog("viewWillAppear: \(self)")
}
}