You should just add UISwipeGestureRecognizer to the main view controller's view.
The main view controller would be responsible for managing the gesture's calls
Basically in code:
in viewDidLoad:
let swipeToLeft = UISwipeGestureRecognizer(target: self, action: #selector(changePageOnSwipe(_:)))
let swipeToRight = UISwipeGestureRecognizer(target: self, action: #selector(changePageOnSwipe(_:)))
swipeToLeft.direction = .right
swipeToRight.direction = .left
self.contentSubView.addGestureRecognizer(swipeToLeft) // Gesture are added to the top view that should handle them
self.contentSubView.addGestureRecognizer(swipeToRight)
Since you will have to move from a VC at an index to another index you might need a property for keeping track of the currently selected view controller:
var currentIndexPath: IndexPath?
And you can change the value of it each time a new VC is selected. So:
func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) {
print("You selected cell #(indexPath.item)!")
self.currentIndexPath = indexPath
// ... Other settings
}
add the changePageOnSwipe(_ gesture: UISwipeGestureRecognizer) method in your main ViewController. Since it is the "chief" view controller who possesses the collectionView, it will handle the swipes and tell its children to appear:
func changePageOnSwipe(_ gesture: UISwipeGestureRecognizer) {
guard let indexPath = self.currentIndexPath else {
// When the page loads and there is no current selected VC, the swipe will not work
// unless you set an initial value for self.currentIndexPath
return
}
var newIndex = indexPath // if self.collectionview.indexPathsForSelectedItems is not empty, you can also use it instead of having a self.currentIndexPath property
// move in the opposite direction for the movement to be intuitive
// So swiping " <-- " should show index on the right (row + 1)
if gesture.direction == .left {
newIndex = IndexPath(row: newIndex.row+1, section: newIndex.section)
} else {
newIndex = IndexPath(row: newIndex.row-1, section: self.currentIndexPath!.section)
}
if canPresentPageAt(indexPath: newIndex) {
// Programmatically select the item and make the collectionView scroll to the correct number
self.collectionview.selectItem(at: newIndex, animated: true, scrollPosition: UICollectionViewScrollPosition.centeredHorizontally)
// The delegate method is not automatically called when you select programmatically
self.collectionView(self.collectionview, didSelectItemAt: newIndex!)
} else {
// Do something when the landing page is invalid (like if the swipe would got to page at index -1 ...)
// You could choose to direct the user to the opposite side of the collection view (like the VC at index self.items.count-1
print("You are tying to navigate to an invalid page")
}
}
and since you are doing the swipe programmatically, you have to make sure that the swipe is valid before trying to actually move. You have to add safety checks:
/** You can use an helper method for those checks
*/
func canPresentPageAt(indexPath: IndexPath) -> Bool {
// Do necessary checks to ensure that the user can indeed go to the desired page
// Like: check if you have a non-nil ViewController at the given index. (If you haven't implemented index 3,4,5,... it should return false)
//
// This method can be called either from a swipe
// or another way when you need it
if indexPath.row < 0 || indexPath.row >= self.items.count {
print("You are trying to go to a non existing page")
return false
} else {
print("If you haven't implemented a VC for page 4 it will crash here")
return true;
}
}
Finally, you can set a default indexPath for self.currentIndexPath in viewDidLoad so that the user can already swipe when he lands on your main VC without having selected another VC in the collectionView.
Note: If you happen to have gesture recognisers in the sub-ViewControllers, some gestures may conflict and you would have to learn how to resolve such conflicts with delegate methods such as gestureRecognizer(_:shouldRequireFailureOf:).
