Detect when UIPickerView starts changing / moving

Question

I'm trying to react to the event that a UIPickerView started moving (not when the row was already selected).

I have searched throughout the delegate methods, and none helped. I also tried to register a notification, but couldn't figure out any that would notify as the user puts his finger on the component and starts scrolling.

Any ideas of what alternatives are there?

Answer 1

You can create a custom class of UIPickerView and override hitTest(point:with:). Creating a protocol, you can send the current picker through a delegate method to your controller and draw whatever you like:

protocol CustomPickerViewDelegate: class {
    func didTapped(_ picker: CustomPickerView)
}

class CustomPickerView: UIPickerView {

    weak var myDelegate: CustomPickerViewDelegate?

    override func hitTest(_ point: CGPoint, with event: UIEvent?) -> UIView? {
        // Only test for points in your needed view
        if !self.point(inside: point, with: event) {
            return nil
        }

        // Return using CustomPickerViewDelegate the current picker
        // that can be used to determine which one was selected
        myDelegate?.didTapped(self)

        // Call super.hitTest(_: with:)
        return super.hitTest(point, with: event)
    }
}

Do NOT forget (in your controller: eg. YourViewController):

self.pickerView.myDelegate = self.

Create an extension of your controller the subscribes to CustomPickerViewDelegate protocol:

extension YourViewController: CustomPickerViewDelegate {
    func didTapped(_ picker: CustomPickerView) {
        // do what you want here
        self.addBorderTo(picker: picker)
    }
}

If you like you can extend the UIPickerViewDelegate (see below how you can extend base class delegate)

Extending a delegate from a base class

Good luck :]