警告：Expression of type ‘UIViewController?’ is unused

// 赋值给_，否则会报Expression of type 'UIViewController?' is unused
_ = self.navigationController?.popViewController(animated: true)

isKindOfClass没有了

// 2.3
viewController.isKindOfClass(PhoneRegViewController)
// 3.0
viewController.isKind(of: PhoneRegViewController.self)

通知也变了

// 2.3
NSNotificationCenter.defaultCenter().postNotificationName("userinfoChanged",object: notification)
// 3.0
NotificationCenter.default.post(name: NSNotification.Name(rawValue: "userinfoChanged"),object: notification)

// 2.3
NSNotificationCenter.defaultCenter().addobserver(self,selector: #selector(currentPageChanged(_:)),name: "loginPageChanged",object: nil)
// 3.0
NotificationCenter.default.addobserver(self,selector: #selector(currentPageChanged),name: NSNotification.Name(rawValue: "loginPageChanged"),object: nil)

zhege

// 2.3
override func touchesEnded(touches: Set<UITouch>,withEvent event: UIEvent?) { txtReply.resignFirstResponder() }
// 3.0
override func touchesEnded(_ touches: Set<UITouch>,with event: UIEvent?) { txtReply.resignFirstResponder() }

// 2.3
btnOk.addTarget(self,action: #selector(okClick(_:)),forControlEvents: .TouchUpInside)
// 3.0
btnOk.addTarget(self,action: #selector(okClick),for: .touchUpInside)

// 2.3
var time = dispatch_time(disPATCH_TIME_Now,Int64(duration * Double(NSEC_PER_SEC)))
    dispatch_after(time,dispatch_get_main_queue()) {
        self.stopAnimating()
}
// 3.0
dispatchQueue.main.asyncAfter(deadline: .Now() +duration) {
    self.stopAnimating()
}

// 2.3
self.arrow.frame = CGRectOffset(arrow.frame,0,0)
// 3.0
self.arrow.frame = arrow.frame.offsetBy(dx: 0,dy: 0)

解决方法