notification

notification.swift

@IBAction func printHello(_ sender: Any) {
    // 消息绑定
    if shouldWaitSwitch.isOn {
        if let _ = shouldWaitSwitch.actions(forTarget: self, forControlEvent: .valueChanged) { // already set
            return
        }
        
        shouldWaitSwitch.addTarget(self, action: #selector(printHello(_:)), for: .valueChanged)
    }
    else {
        print("你好！")
    
        if let _ = shouldWaitSwitch.actions(forTarget: self, forControlEvent: .valueChanged) { // if set
            shouldWaitSwitch.removeTarget(self, action: #selector(printHello(_:)), for: .valueChanged)
        }
    }
}

@IBOutlet weak var shouldWaitSwitch: UISwitch!