Enabling native overflow scrolling on supported platforms.

[Martin Kleinschrodt]

I recently tried to use native overflow scrolling in an Enyo application on iOS7 and KitKat via '-webkit-overflow-scrolling: touch' and was surprised to see that it didn't work. Digging into enyo core, I found this (https://github.com/enyojs/enyo/blob/master/source/touch/touch.js#L34-L39):

// prevent default document scrolling if enyo.bodyIsFitting == true

// avoid window scrolling by preventing default on this event

// note: this event can be made unpreventable (native scrollers do this)

if (enyo.bodyIsFitting) {

    inEvent.preventDefault();

}

Is there any specific reason for this, apart from preventing the overflow scrolling on the document itself? I feel like this should be removed, if only to allow people to use native overflow scrolling if they choose to do so.

[Ben Combee]

IIRC (and it's been a while), one of the problems with the native scroller is that it didn't provide timely events about the scroll position, which meant it wasn't usable with our List implementation as the list didn't get notified to refresh it's visible set of elements.  That shouldn't prevent its use for content you've fully generated, but someone doing active dev may be able to provide more color.

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[Martin Kleinschrodt]

Great to see you're still watching the mailing list, Ben! Yeah, I'm aware of the list problems but as you said that's really no reason to prevent the default behavior of the touchmove event.

[Martin Kleinschrodt]

Really? Ben's the only one who's watching the mailing list? That's kinda sad...

[Cole Davis]

I think Ben's answer is very accurate. The code you are referring to was added back in early 2012 (before I was on the team) and was solving a compatibility issue that may/may-not be as large a factor for modern browsers. I tracked the path of code relying on the behavior and it looks like having a way to disable it could be useful but would probably disable other features of non-native scrollers potentially. The impacts across the board would need to be traced – specifically TouchScrollStrategy.

Cheers,

Cole

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