iOS/Swift: how to detect touch action on a UITextField

It seems “Touch Up Inside” is not enabled for UITextField, but “Touch Down” works.

So the solution is as follows:

Swift 4.x

myTextField.addTarget(self, action: #selector(myTargetFunction), for: .touchDown)
@objc func myTargetFunction(textField: UITextField) {
    print("myTargetFunction")
}

Swift 3.x

myTextField.addTarget(self, action: #selector(myTargetFunction), for: UIControlEvents.touchDown)

@objc func myTargetFunction(textField: UITextField) {
    print("myTargetFunction")
}