How to measure touch pressure (keystroke) on iOS system keyboard?

Question

Probably there is no way to measure touch pressure using a custom UIGestureRecognizer, since we cannot directly access the system keyboard's view [1]. It can be achieved if a custom inputViewController is used but it's not an option for me. I want to store key hold time and key press pressure for each key. Do you know a way to do this?

Edit: [1] I said "We cannot directly access the system keyboard's view." but actually we can: UIRemoteKeyboardWindow > InputSetContainerView > InputSetHostView.

I think that an improvement to Nirav Bhatt's answer may solve this issue but it disables the functionality of touches on the keyboard view. When I touch on a key, it outputs force of touch but the corresponding letter isn't typed to text field.

Answer 1

The solution is easier than I think. For iOS 9+ systems, we can follow these steps to access system keyboard and listen keystroke...

At first, create a custom UIGestureRecognizer to listen keystroke. The implementation of this step is skipped, since it's trivial (just override touchesBegan, touchesMoved, touchesEnded).

Add KeyboardManager to access keyboard view:

final class KeyboardManager {

    static let shared = KeyboardManager()

    private init() { }

    /// Returns keyboard view on application window
    ///
    /// - Returns: Keyboard view
    func keyboardView() -> UIView? {
        for window in UIApplication.shared.windows {
            if let keyboardView = keyboardViewFromWindow(window) {
                return keyboardView
            }
        }
        return nil
    }

    /// Returns keyboard view from given window
    ///
    /// - Parameter window: Keyboard view container candidate window
    /// - Returns: Keyboard view
    func keyboardViewFromWindow(_ window: UIWindow) -> UIView? {
        if window.hasClassNameSuffix("UIRemoteKeyboardWindow") {
            let inputSetContainerView = window.subview(withSuffix: "InputSetContainerView")
            let inputSetHostView = inputSetContainerView?.subview(withSuffix: "InputSetHostView")
            return inputSetHostView
        }

        return nil
    }
}

UIView extension functions used above:

@nonobjc extension UIView {

    /// Returns first found subview with given class name
    ///
    /// - Parameter className: Subview class name
    /// - Returns: First subview with given class name
    func subview(withSuffix className: String) -> UIView? {
        return subviews.first {
            $0.hasClassNameSuffix(className)
        }
    }

    /// Compares suffix of view class name with given name
    ///
    /// - Parameter className: Class name that will be compared
    /// - Returns: Comparison result of view class name and given name
    func hasClassNameSuffix(_ className: String) -> Bool {
        return NSStringFromClass(type(of: self)).hasSuffix(className)
    }
}

Then, add your gesture recognizer to keyboard view using below functions:

KeyboardManager.shared.keyboardView()?.addGestureRecognizer(keyboardGestureRecognizer).

Note: Your gesture recognizer shouldn't extend UITapGestureRecognizer. UILongPressGestureRecognizer is okay. We cannot add multiple tap gesture recognizers with same type to a view.