How do I detect a “command + backspace” from an external keyboard in a UITextField

Question

I am using the good old add a zero length character solution to detect backspaces in an empty text field ( Detect backspace Event in UITextField ).

Unfortunately on an iPad if you connect an external keyboard and hit "cmd+backspace" it does not trigger the shouldChangeCharactersInRange method.

I looked around the documentation and the decompiled headers and I don't seem to be able to find a way to prevent that.

So, how do I detect a "command + backspace event"?

Answer 1

You can use a UIKeyCommand . I tested on my 10.5" iPad Pro running iOS 12.1.1, using a Bluetooth keyboard and the Swift Playgrounds app version 2.2.

Here's the playground code:

import UIKit
import PlaygroundSupport

class ViewController: UIViewController {
    override func loadView() {
        let command = UIKeyCommand(input: "\u{8}", modifierFlags: .command, action: #selector(ViewController.handleKeyCommand), discoverabilityTitle: "Hello")
        addKeyCommand(command)

        let view = UIView(frame: CGRect(x: 0, y: 0, width: 300, height: 300))
        view.contentMode = .topLeft
        view.backgroundColor = .white

        let stack = UIStackView()
        stack.axis = .vertical
        stack.spacing = 8
        stack.alignment = .fill
        stack.translatesAutoresizingMaskIntoConstraints = false
        view.addSubview(stack)
        NSLayoutConstraint.activate([
            view.leadingAnchor.constraint(equalTo: stack.leadingAnchor),
            view.trailingAnchor.constraint(equalTo: stack.trailingAnchor),
            view.topAnchor.constraint(equalTo: stack.topAnchor)])

        let textField = UITextField(frame: CGRect(x: 20, y: 20, width: 260, height: 30))
        textField.borderStyle = .roundedRect
        textField.translatesAutoresizingMaskIntoConstraints = false
        stack.addArrangedSubview(textField)

        label.translatesAutoresizingMaskIntoConstraints = false
        stack.addArrangedSubview(label)

        self.view = view
    }

    @objc func handleKeyCommand(_ sender: UIKeyCommand) {
        commandCount += 1
        label.text = "\(commandCount)"
    }

    private var commandCount = 0
    private let label = UILabel()
}

let vc = ViewController()
PlaygroundPage.current.liveView = vc

Tap in the text field, then press ⌘⌫ . Each time you press it, the count in the label increases by 1.