Пример в Swift от Xcode 7.2.1 и OS X 10.11:
let a = NSAlert()
a.messageText = "Please enter a value"
a.addButtonWithTitle("Save")
a.addButtonWithTitle("Cancel")
let inputTextField = NSTextField(frame: NSRect(x: 0, y: 0, width: 300, height: 24))
inputTextField.placeholderString = "Enter string"
a.accessoryView = inputTextField
a.beginSheetModalForWindow(self.window!, completionHandler: { (modalResponse) -> Void in
if modalResponse == NSAlertFirstButtonReturn {
let enteredString = inputTextField.stringValue
print("Entered string = \"\(enteredString)\"")
}
})