How does Piictu implement both vertical and horizontal scrolling?

The main view of the iOS app "Piictu" i开发者_如何学运维s a vertical scrolling list of photo albums. The thumbnails of each album are displayed inline and scroll horizontally.

If you swipe down or up from any point the parent view scrolls vertically, even when the starting point of the gesture on an album thumbnail.

What's your best understanding of how this is done? A vertical swipe gesture recognizer on the parent view and a horizontal swipe gesture recognizer on the album child/sub views?

Or, is this perhaps a UIWebView?

Thanks!

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It's a lot simpler than that, or at least it can be done a lot simpler: just nest scroll views. The outer one covers the whole screen and only allowing vertical scrolling. Each series of thumbnails is contained in another, smaller scroll view which only allows horizontal scrolling. I've used this technique myself for an app I was contracted to develop.