Nested Controllers using UICollectionViewController reordering - ios

Question

I have a UIViewController with a UICollectionViewController nested inside. The collection view controller also has the moveItemAt method implemented, since I want the cells to be reorderable. So the cells have a UILongPressGestureRecognizer attached. However, long press on the cells aren't happening. I can't seem to figure out if the nested controller is causing the gesture to be ignored. Maybe the parent controller is capturing the long press but that wouldn't make sense since AFAIK, gestures go up the view hierarchy, not the other way around.
For some context, I've used this method to nest my controllers
func add(_ child: UIViewController) {
addChildViewController(child)
child.view.frame = view.bounds
view.addSubview(child.view)
child.didMove(toParentViewController: self)
}

Answer 1

I think this is a better approach...
Assuming you have a UICollectionViewController in your storyboard, and you've assigned the cell prototype to DragMeCell and set its Identifier to "DragMeCell" (and added a label connected to the IBOutlet), this should run and allow you to long-press drag-drop to reorder.
//
// DragReorderCollectionViewController.swift
// SW4Temp
//
// Created by Don Mag on 7/25/18.
//
import UIKit
private let reuseIdentifier = "DragMeCell"
class DragMeCell: UICollectionViewCell {
#IBOutlet var theLabel: UILabel!
}
class DragReorderCollectionViewController: UICollectionViewController {
fileprivate var longPressGesture: UILongPressGestureRecognizer!
fileprivate var dataArray = Array(0 ..< 25)
override func viewDidLoad() {
super.viewDidLoad()
longPressGesture = UILongPressGestureRecognizer(target: self, action: #selector(self.handleLongGesture(gesture:)))
if let cv = self.collectionView {
cv.addGestureRecognizer(longPressGesture)
}
}
#objc func handleLongGesture(gesture: UILongPressGestureRecognizer) {
if let cv = self.collectionView,
let gestureView = gesture.view {
switch(gesture.state) {
case .began:
guard let selectedIndexPath = cv.indexPathForItem(at: gesture.location(in: cv)) else {
break
}
cv.beginInteractiveMovementForItem(at: selectedIndexPath)
case .changed:
cv.updateInteractiveMovementTargetPosition(gesture.location(in: gestureView))
case .ended:
cv.endInteractiveMovement()
default:
cv.cancelInteractiveMovement()
}
}
}
// MARK: UICollectionViewDelegate
override func collectionView(_ collectionView: UICollectionView, canMoveItemAt indexPath: IndexPath) -> Bool {
return true
}
override func collectionView(_ collectionView: UICollectionView, moveItemAt sourceIndexPath: IndexPath, to destinationIndexPath: IndexPath) {
let i = dataArray[sourceIndexPath.item]
dataArray.remove(at: sourceIndexPath.item)
dataArray.insert(i, at: destinationIndexPath.item)
}
// MARK: UICollectionViewDataSource
override func numberOfSections(in collectionView: UICollectionView) -> Int {
return 1
}
override func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
return dataArray.count
}
override func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
let cell = collectionView.dequeueReusableCell(withReuseIdentifier: reuseIdentifier, for: indexPath) as! DragMeCell
// Configure the cell
cell.theLabel.text = "\(dataArray[indexPath.item])"
return cell
}
}
Then you can add it as a child view controller, using the code snippet you posted in your question.