Get the current first responder without using a private API

Question

I submitted my app a little over a week ago and got the dreaded rejection email today. It tells me that my app cannot be accepted because I\'m using a non-public API; specif

Answer 1

I have a slightly different approach than most. Rather than iterate through the collection of views looking for the one that has isFirstResponder set, I too send a message to nil, but I store the receiver of the message so I can return it and do whatever I wish with it.

import UIKit

private var _foundFirstResponder: UIResponder? = nil

extension UIResponder {

    static var first:UIResponder? {

        // Sending an action to 'nil' implicitly sends it to the first responder
        // where we simply capture it and place it in the _foundFirstResponder variable.
        // As such, the variable will contain the current first responder (if any) immediately after this line executes
        UIApplication.shared.sendAction(#selector(UIResponder.storeFirstResponder(_:)), to: nil, from: nil, for: nil)

        // The following 'defer' statement runs *after* this getter returns,
        // thus releasing any strong reference held by the variable immediately thereafter
        defer {
            _foundFirstResponder = nil
        }

        // Return the found first-responder (if any) back to the caller
        return _foundFirstResponder
    }

    @objc func storeFirstResponder(_ sender: AnyObject) {

        // Capture the recipient of this message (self), which is the first responder
        _foundFirstResponder = self
    }
}

With the above, I can resign the first responder by simply doing this...

UIResponder.first?.resignFirstResponder()

But since my API actually hands back whatever the first responder is, I can do whatever I want with it.

Here's an example that checks if the current first responder is a UITextField with a helpMessage property set, and if so, shows it in a help bubble right next to the control. We call this from a 'Quick Help' button on our screen.

func showQuickHelp(){

    if let textField   = UIResponder?.first as? UITextField,
       let helpMessage = textField.helpMessage {
    
        textField.showHelpBubble(with:helpMessage)
    }
}

The support for the above is defined in an extension on UITextField like so...

extension UITextField {
    var helpMessage:String? { ... }
    func showHelpBubble(with message:String) { ... }
}

Now to support this feature, all we have to do is decide which text fields have help messages and the UI takes care of the rest for us.