当UITextField满或为空时显示警报

这是一个很好的例子

guard

@IBAction func LoginBtn(sender: AnyObject) {   guard let userName = userNameTF.text where !userName.isEmpty else {        displayMyalertMessage ("Forget to fill your user name")        return   }   guard let password = passwordTF.text where !password.isEmpty else {        displayMyalertMessage ("Forget to fill your password")        return   }    // do something with userName and password}