Unable to swipe/drag between values with new iOS modal presentation style

[benpackard]

iOS 13 introduced a new default modal presentation style that allows the user to dismiss with a downwards gesture. Unfortunately this interferes with dragging from one star rating to another in Cosmos.

To reproduce:

1. Add a CosmosView to a view controller and present it modally on iOS 13.
2. Attempt to drag your finger from one star to the next

Expected: the star rating changes as the user drags her finger

Actual: the star rating does not change

A few observations:

• I am using the latest version of Cosmos and iOS 13.1.1
• The CosmosView works as expected if the view controller's modalPresentationStyle is changed to .fullScreen
• On close inspection, a drag gesture does allow for value changes of half-step increments, but as soon as the gesture leaves one star for the next star, the gesture is dropped.
• Setting the parent scroll view's canCancelContentTouches to false does not seem to help.
• Setting passTouchesToSuperview to false does not help.

[benpackard]

Some screen recordings:

Working (full screen).

Not working (partial modal).

[benpackard]

I've confirmed that didFinishTouchingCosmos fires as the gesture leaves the edge of the star that initiated it. Without knowing to much about how gestures work, perhaps Cosmos doesn't expect to be added on top of another gesture and the new modal 'dismiss' gesture is picking up the drag as soon as it hits the gap between stars?

This might be helpful: https://stackoverflow.com/questions/56718552/disable-gesture-to-pull-down-form-page-sheet-modal-presentation

[benpackard]

Here is the workaround I am using now based on the stackoverflow answer above. It's very naive but it works. Let me know if this would make for a good PR. There are probably some other consequences I am not considering here.

private class FixedCosmosView: CosmosView {
	override func gestureRecognizerShouldBegin(_ gestureRecognizer: UIGestureRecognizer) -> Bool {
		return !(gestureRecognizer is UIPanGestureRecognizer)
	}
}

[evgenyneu]

Hi @benpackard. Holy! This is an amazing bug report, thank you very much. And thanks for finding a workaround (gestureRecognizerShouldBegin). It works very well inside a modal screen, same way it works usually.

However, I noticed that this workaround changes things a bit when Cosmos view is inside a table view. In order to see that, click "Performance button" in the top right corner of the Demo app, as shown on Fig. 1. It will show a table view with many rating controls.

Now, without your workaround, one can scroll through the table view by touching anywhere in the table view, including a cosmos view (see Fig. 2). After I included your workaround, however, I could not scroll the table when my scroll gesture started within a Cosmos view.

What do you think we should do here? If we add this workaround as it is, it might introduce these scrolling issues to existing apps and people will be angry. Maybe we can add a flag in Cosmos settings, disablePanGenstures, which is false by default? Also we could add a note to Readme to do

cosmosView.settings.disablePanGenstures = true

in order to make Cosmos work in the modal screens?

Figure 1: Opening a table view in a demo app

Figure 2: Scrolling table view by first touching the Cosmos rating view.

[benpackard]

@evgenyneu A flag sounds like the right path forward. I do wonder though what happens for a table view in a modal, where the user might need both behaviors. If I get some time this evening I'll test that scenario out.

[evgenyneu]

@benpackard, thanks. Feel free to submit a pull request, if you want.

[benpackard]

Submitted a pull request, hope I didn't miss anything!

[gunnarsson]

I ran into this problem and solved using the flag mentioned above. Thanks!

My preferred fix (without knowing much about the implementation) would be that pan events that are initially mostly vertical are allowed and lets the user scroll the parent view, but that mostly horizontal pan events are captured and used to adjust the rating. Would this be possible? This behaviour is common throughout iOS, one example is the Mail app. If you begin swiping a mail horizontally it's not possible to scroll the list until you've ended the gesture, and the other way around.