Swift Swizzled

objc中出于安全性和一致性考虑，用+(void)load()来实现

swift中load()方法不起作用了，在swift中写load()方法编译器会提示错误，

可以用initialize() 或者是直接写在application(application: UIApplication, didFinishLaunchingWithOptions launchOptions: [NSObject:AnyObject]?) -> Bool

下面是在initialize() 实现的例子，修改项目中所有UIViewController的背景色

新建一个项目SwiftAlbum，为了代码修改起来方便，新建了一个AppLoad.swift文件

import UIKit

extension UIViewController {
public override class func initialize() {

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

struct DispatchToken {
static var token: dispatch_once_t = 0
}

dispatch_once(&DispatchToken.token) {
let originalSelector = #selector(UIViewController.viewDidLoad)
let swizzledSelector = #selector(self.lw_viewDidLoad)

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

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

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

}
}

func lw_viewDidLoad() {
print("viewDidLoad: \(NSStringFromClass(self.classForCoder))")
let albumClassName = NSStringFromClass(self.classForCoder)
if albumClassName.containsString("SwiftAlbum") {
self.view.backgroundColor = UIColor.init(colorLiteralRed: 244/255, green: 244/255, blue: 244/255, alpha: 1)
}
}
}

class AppLoad: NSObject {

}

通过print(“viewDidLoad:(NSStringFromClass(self.classForCoder))”)打印可以看到，项目中新建的UIViewController，都有一个工程名前缀，比如SwiftAlbum.XXXViewController

参考地址：http://nshipster.com/swift-objc-runtime/