Swift: record touch force, size, duration

Question

For a data analysis project, I want to track the measurements for touch force, size and duration in a log-file for a simple app (I use the Foodtracker app from the Apple Documentation Website).

I know that I can get the force, size and duration from UITouch. But

1. how do I access UITouch to get these measurements?
2. and how do I write these measurements into a log-file?

Answer 1

1. How do I access UITouch to get these measurements?

You'll have to override the touch handlers in your view controller.

override func touchesBegan(_ touches: Set<UITouch>, with event: UIEvent?) {
    super.touchesBegan(touches, with: event)
    let touch = touches.first!
    print("\(touch.force)")
    print("\(touch.majorRadius)")
    print("\(touch.timestamp)")
}

override func touchesMoved(_ touches: Set<UITouch>, with event: UIEvent?) {
    super.touchesMoved(touches, with: event)
    let touch = touches.first!
    print("\(touch.force)")
    print("\(touch.majorRadius)")
    print("\(touch.timestamp)")
}

override func touchesCancelled(_ touches: Set<UITouch>, with event: UIEvent?) {
    super.touchesCancelled(touches, with: event)
    let touch = touches.first!
    print("\(touch.force)")
    print("\(touch.majorRadius)")
    print("\(touch.timestamp)")
}

2. How do I write these measurements into a log-file?

For that checkout this post: Read and write a String from text file