UIPageViewController Swipe Conditional On UIScrollView - ios

Question

I've seen a similar question here but with no working solution.
I have a UIScrollView that is embedded in a UIPageViewController. I would like to have the user able to scroll the UIScrollView normally. Then, if one end of the UIScrollView is reached (all the way to the left, for example) then swiping left (swiping right, but you get what I mean) would trigger the UIPageViewController to shift left to another page.
The default behavior is a bit sketchy. It seems like the gesture recognizers compete and in some cases the UIScrollView does scroll, and in other cases the PageView just shifts to the next page. I'd like to be able to tie this behavior to the content offset of the UIScrollView, or something.
I'll be trying some experiments with the requireFail methods on the various gesture recognizers, but it seems like all of the PageView's gesture recognizer properties are nil'd out because I'm using the scroll transition type. So...walking the hierarchy?
Anyway, I'd appreciate it if anyone knows an easy solution to this.

Answer 1

The way I ended up solving this was by using a replacement for UIPageViewController: EMPageViewController. Because I had direct access to the UIScrollView, I was able to subclass it.
The solution basically came in subclassing and adding toggle flags to the UIScrollViews (the one FOR the EMPageViewController and the one INSIDE it) to control when they should be active or not, based on various factors (such as the content offset of one of the scroll views). Then I was able to override gestureRecognizerShouldBegin:gestureRecognizer in different ways in the UIScrollView subclasses, checking the toggle flags and the velocity of the panning gesture recognizer.
Something like this (code out of context):
import UIKit
class CustomScrollView: UIScrollView {
// these toggles get set by some senior ViewController
var lockDown = false
var lockUp = false
override func gestureRecognizerShouldBegin(gestureRecognizer: UIGestureRecognizer) -> Bool {
print("= gesture starting")
if let panner = gestureRecognizer as? UIPanGestureRecognizer {
if panner.velocityInView(self).y < 0.0 {
print("== pulling down, lockDown: \(lockDown)")
if lockDown {
print("=== cancelling paging scroll")
return false
}
}
if panner.velocityInView(self).y > 0.0 {
print("== pulling up, lockUp: \(lockUp)")
if lockUp {
print("=== cancelling paging scroll")
return false
}
}
}
return super.gestureRecognizerShouldBegin(gestureRecognizer)
}
}
Anyway, I did get it all working slickly in the end. Everyone would probably have a slightly different use case, but the bottom line is that you need to subclass UIScrollView and so UIPageViewController is not an option.