swift中没有dispatch_once。代替使用static let， 是线程安全性质的，
swift中想要某个代码只执行一次
private static let takeOnce: Void = {
//代码块。。。。
}()
swift中想要再load 和initialize 阶段搞事情。改怎么办？？>
思路： UIApplication有一个next属性。它会在applicationDidFinishLanching之前被调用,通过runtime获取到所有类的列表，然后向所有遵循SelfAware协议的类发送消息
extension UIApplication {
private static let runOnce: Void = {
SwizzlingTool.searchAndExecuteAwake()
}()
override open var next: UIResponder? {
UIApplication.runOnce
return super.next
}
protocol SelfAware: AnyObject {
static func awake()
static func swizzlingForClass(_ forClass: AnyClass, originalSelector: Selector, swizzledSelector: Selector)
}
extension SelfAware {
static func swizzlingForClass(_ forClass: AnyClass, originalSelector: Selector, swizzledSelector: Selector) {
let originalMethod = class_getInstanceMethod(forClass, originalSelector)
let swizzledMethod = class_getInstanceMethod(forClass, swizzledSelector)
guard originalMethod != nil && swizzledMethod != nil else {return}
if class_addMethod(forClass, originalSelector, method_getImplementation(swizzledMethod!), method_getTypeEncoding(swizzledMethod!)) {
class_replaceMethod(forClass, swizzledSelector, method_getImplementation(originalMethod!), method_getTypeEncoding(originalMethod!))
} else {
method_exchangeImplementations(originalMethod!, swizzledMethod!)
}
}
}
参考文章：https://www.codercto.com/a/39074.html
