Obtenga el valor de entrada de TextField en la alerta de iOS en Swift

Estoy tratando de crear un mensaje de alerta con entrada y luego obtener el valor de la entrada. Encontré muchos buenos tutoriales sobre cómo hacer el campo de entrada de texto. pero no puedo obtener el valor de la alerta.

Actualizado para Swift 3 y superior:

//1. Create the alert controller.
let alert = UIAlertController(title: "Some Title", message: "Enter a text", preferredStyle: .alert)

//2. Add the text field. You can configure it however you need.
alert.addTextField { (textField) in
    textField.text = "Some default text"
}

// 3. Grab the value from the text field, and print it when the user clicks OK.
alert.addAction(UIAlertAction(title: "OK", style: .default, handler: { [weak alert] (_) in
    let textField = alert.textFields![0] // Force unwrapping because we know it exists.
    print("Text field: \(textField.text)")
}))

// 4. Present the alert.
self.present(alert, animated: true, completion: nil)

Swift 2.x

Suponiendo que desea una alerta de acción en iOS:

//1. Create the alert controller.            
var alert = UIAlertController(title: "Some Title", message: "Enter a text", preferredStyle: .Alert)

//2. Add the text field. You can configure it however you need.
alert.addTextFieldWithConfigurationHandler({ (textField) -> Void in
    textField.text = "Some default text."
})

//3. Grab the value from the text field, and print it when the user clicks OK. 
alert.addAction(UIAlertAction(title: "OK", style: .Default, handler: { [weak alert] (action) -> Void in
    let textField = alert.textFields![0] as UITextField
    println("Text field: \(textField.text)")
}))

// 4. Present the alert.
self.presentViewController(alert, animated: true, completion: nil)

Rápido 3/4

Puede usar la siguiente extensión para su conveniencia.

Uso dentro de un ViewController:

showInputDialog(title: "Add number",
                subtitle: "Please enter the new number below.",
                actionTitle: "Add",
                cancelTitle: "Cancel",
                inputPlaceholder: "New number",
                inputKeyboardType: .numberPad)
{ (input:String?) in
    print("The new number is \(input ?? "")")
}

El código de extensión:

extension UIViewController {
    func showInputDialog(title:String? = nil,
                         subtitle:String? = nil,
                         actionTitle:String? = "Add",
                         cancelTitle:String? = "Cancel",
                         inputPlaceholder:String? = nil,
                         inputKeyboardType:UIKeyboardType = UIKeyboardType.default,
                         cancelHandler: ((UIAlertAction) -> Swift.Void)? = nil,
                         actionHandler: ((_ text: String?) -> Void)? = nil) {

        let alert = UIAlertController(title: title, message: subtitle, preferredStyle: .alert)
        alert.addTextField { (textField:UITextField) in
            textField.placeholder = inputPlaceholder
            textField.keyboardType = inputKeyboardType
        }
        alert.addAction(UIAlertAction(title: actionTitle, style: .default, handler: { (action:UIAlertAction) in
            guard let textField =  alert.textFields?.first else {
                actionHandler?(nil)
                return
            }
            actionHandler?(textField.text)
        }))
        alert.addAction(UIAlertAction(title: cancelTitle, style: .cancel, handler: cancelHandler))

        self.present(alert, animated: true, completion: nil)
    }
}

En Swift5 y Xcode 10

Agregue dos campos de texto con las acciones Guardar y Cancelar y lea datos de texto de TextFields

func alertWithTF() {
    //Step : 1
    let alert = UIAlertController(title: "Great Title", message: "Please input something", preferredStyle: UIAlertController.Style.alert )
    //Step : 2
    let save = UIAlertAction(title: "Save", style: .default) { (alertAction) in
        let textField = alert.textFields![0] as UITextField
        let textField2 = alert.textFields![1] as UITextField
        if textField.text != "" {
            //Read TextFields text data
            print(textField.text!)
            print("TF 1 : \(textField.text!)")
        } else {
            print("TF 1 is Empty...")
        }

        if textField2.text != "" {
            print(textField2.text!)
            print("TF 2 : \(textField2.text!)")
        } else {
            print("TF 2 is Empty...")
        }
    }

    //Step : 3
    //For first TF
    alert.addTextField { (textField) in
        textField.placeholder = "Enter your first name"
        textField.textColor = .red
    }
    //For second TF
    alert.addTextField { (textField) in
        textField.placeholder = "Enter your last name"
        textField.textColor = .blue
    }

    //Step : 4
    alert.addAction(save)
    //Cancel action
    let cancel = UIAlertAction(title: "Cancel", style: .default) { (alertAction) in }
    alert.addAction(cancel)
    //OR single line action
    //alert.addAction(UIAlertAction(title: "Cancel", style: .default) { (alertAction) in })

    self.present(alert, animated:true, completion: nil)

}

Para obtener más explicación https://medium.com/@chan.henryk/alert-controller-with-text-field-in-swift-3-bda7ac06026c