在按钮外开始触摸并在拖入按钮边界时触发事件

Question

If I have a button and starts a touch outside of the buttons bounds and then drag my finger across the screen until I hit the bounds of the button which then will trigger an event. Say change the background color of the button for example (which I know how to). How do I trigger something from that type of touch movement?

I also set my buttons programmatically.

Thanks in advance!

Answer 1

To trigger an action attached to a button when a finger is moving over the button you can use a method touchesMoved(_:with:) of UIViewController.

Firstly, add an action to the button for touchUpInside and touchDragInside inside InterfaceBuilder or in code.

Secondly, override touchesMoved(_:with:) method and call a super. If the super is not called the button UIKit will not trigger any actions on the button. Next, get a touch location inside the view and trigger a touchDragInside action on the button.

@IBOutlet weak var button: UIButton!

override func touchesMoved(_ touches: Set<UITouch>, with event: UIEvent?) {
    super.touchesMoved(touches, with: event)
    if let t = touches.first,
        button.frame.contains(t.location(in: view)) {
        button.sendActions(for: .touchDragInside)
    } else {
        print("false")
    }
}

@IBAction
func didTapButton() {
    print("true: touch inside the frame of a button")
}

@IBAction
func didDragInsideButton() {
    print("true: touch drag inside the frame of a button")
}

override func touchesBegan(_ touches: Set<UITouch>, with event: UIEvent?) {
}

override func viewDidLoad() {
    super.viewDidLoad()

    button.addTarget(self, action: #selector(didTapButton), for: .touchUpInside)
    button.addTarget(self, action: #selector(didDragInsideButton), for: .touchDragInside)
}