How to open the keyboard automatically on UITextField?

Swift 3 & 4:

override func viewDidAppear(_ animated: Bool) {
    super.viewDidAppear(animated)
    textField.becomeFirstResponder()
}

To cause the keyboard to show up immediately you'll need to set the text field as the first responder using the following line:

[textField becomeFirstResponder];

You may want to place this in the viewDidAppear: method.