[SwipeActions] Limit overscrolling to the right

[nononoah]

Summary

Though Listable does not support actions beneath the left of the cell, it is currently possible to swipe the contents of a cell all the way to the right. This leads to unexpected and undesirable visual state.

This PR caps overscroll to the right to 20% of the width of the cell. As a result, we maintain a certain bounciness, but don't allow for wilder translations.

Demo

Before

https://user-images.githubusercontent.com/1542313/109521585-78221e00-7a7b-11eb-846c-c04962cf200d.mov

After

https://user-images.githubusercontent.com/1542313/109521619-7fe1c280-7a7b-11eb-8676-d7b00faf1e4c.mov

[kyleve]

Mind adding a note to the changelog in the root of the repo as well?

[nononoah]

Mind adding a note to the changelog in the root of the repo as well?

Added!

[kylebshr]

Can I suggest an additional change that doesn't allow you start a swipe in this direction, which mimics the built-in swipe actions? (This should stay since you can still swipe this was after starting a swipe). Happy to PR that change myself, or walk you through what I have in mind

[nononoah]

Thanks for the suggestion,@kylebshr. It definitely improves the feel of the cell.

I took a shot at implementing this, and arrived at the following:

case .began, .changed:

    if swipeState == .closed && velocity > 0 {
        // The cell is closed and this is a swipe to the right. Ignore the swipe.
        sender.setTranslation(.zero, in: self)
    } else {
        let swipeState = SwipeActionState.swiping(willPerformAction: willPerformAction)
        set(state: swipeState)
    }

sender.setTranslation(.zero, in: self) is important so that we don't "jump" when the swipe that begins to the right starts moving back to the left.

If you have other ideas or would like the logic spelled differently (e.g. case .began, .changed where ...), please let me know and I'll update before merging.

[kylebshr]

My one thought is that those could perhaps be implemented in the gesture recognizer itself (HorizontalGestureRecognizer.swift I think?), in much the same way that it ignores vertical swipes. That might clean up the logic here, since the gesture will cancel and never start if the velocity is incorrect.

[kylebshr]

Awesome, thanks! We'll probably need to update this eventually when we add support for trailing and/or leading actions, but we can tackle that when we get to it!