Cannot reorder Collection View cells

Question

I have a Split View Controller and when the user clicks a cell in the Table View, the app shows a View Controller with a Container View and a Segment Control to switch between two children view controllers.

The first child view controller is a Collection View Controller. In every cell of the Collection View there is a word.

The view looks like this:

I add the child view controller programmatically with this code (from the Detail View Controller, the container of Subviews):

override func viewDidLoad() {


    self.currentViewController = self.storyboard?.instantiateViewController(withIdentifier: "WordCollectionViewControllerID")
    (self.currentViewController as! WordCollectionViewController).text = self.text
    self.currentViewController?.view.translatesAutoresizingMaskIntoConstraints = false
    self.addChildViewController(self.currentViewController!)
    self.addSubview(subView: self.currentViewController!.view, toView: self.textContainerView)
    self.currentViewController?.view.layoutIfNeeded()
    self.currentViewController?.didMove(toParentViewController: self)

    super.viewDidLoad()

}

func addSubview(subView: UIView, toView parentView: UIView) {
    parentView.addSubview(subView)

    var viewBindingsDict = [String: AnyObject]()
    viewBindingsDict["subView"] = subView
    parentView.addConstraints(NSLayoutConstraint.constraints(withVisualFormat: "H:|[subView]|", options: [], metrics: nil, views: viewBindingsDict))
    parentView.addConstraints(NSLayoutConstraint.constraints(withVisualFormat: "V:|[subView]|", options: [], metrics: nil, views: viewBindingsDict))
}

Here is the code for switch between the two children views with the segmented control:

@IBAction func changeChildViewController(_ sender: UISegmentedControl) {
    if sender.selectedSegmentIndex == 0 {
        let newViewController = self.storyboard?.instantiateViewController(withIdentifier: "WordCollectionViewControllerID")
        (newViewController as! WordCollectionViewController).text = self.text
        newViewController!.view.translatesAutoresizingMaskIntoConstraints = false
        cycle(from: self.currentViewController!, to: newViewController!)
        self.currentViewController = newViewController
        print("Reorder")
    } else {
        let newViewController = self.storyboard?.instantiateViewController(withIdentifier: "NavigationControllerEditTextViewControllerID")
        (newViewController?.childViewControllers[0] as! EditTextViewController).text = self.text
        newViewController!.view.translatesAutoresizingMaskIntoConstraints = false
        cycle(from: self.currentViewController!, to: newViewController!)
        self.currentViewController = newViewController
        print("Edit")
    }
}

func cycle(from: UIViewController, to: UIViewController) {
    from.willMove(toParentViewController: nil)
    self.addChildViewController(to)

    self.addSubview(subView: to.view, toView: self.textContainerView)

    to.view.layoutIfNeeded()

    from.view.removeFromSuperview()

    from.removeFromParentViewController()
    to.didMove(toParentViewController: self)
}

To be able to reorder the cells I have implemented this method for my custom CollectionViewController class:

override func collectionView(_ collectionView: UICollectionView, moveItemAt sourceIndexPath: IndexPath, to destinationIndexPath: IndexPath) {

    // Swap values if sorce and destination
    let change = textArray[sourceIndexPath.row]


    textArray.remove(at: sourceIndexPath.row)
    textArray.insert(change, at: destinationIndexPath.row)


    // Save changes in Core Data
    text?.reordered_text = textArray.joined(separator: " ")

    (UIApplication.shared.delegate as! AppDelegate).saveContext()


    collectionView.reloadData()
}

The problem is that when I click the Table View Cell and the app shows the Container View with the Collection View Controller embedded, I can't reorder the cells,and to be able to do this I have to change the Child (with the Segmented Control) and then return to the Collection View.

How can I solve this problem?

Sorry if I've made some mistakes with the language, I am italian — alessionossa, Sep 13 '16 at 14:13
In your question you said, on tableview cell selection you are showing the collection view. How are you doing it? and how are you triggering cell reload? — Aks, Sep 13 '16 at 14:24
I have edited to explain better. I use a Storyboard Segue to open the container view @Aks — alessionossa, Sep 13 '16 at 14:29
Can you paste code on what happens when you switch via segmented control — vj9, Sep 16 '16 at 09:43

score 0 · Answer 1 · answered Sep 16 '16 at 14:33

I would check two things:

Firstly you call willMoveToParentViewController in your cycle(from: UIViewController, to: UIViewController) method, but not in viewDidLoad, try to do this. From what I can read you should be able to call cycle in your viewDidLoad method, calling a method on a Nil-object (from) does nothing.

Secondly check if your WordCollectionViewController collectionView delegate and dataSource are set properly when it loads the first time. These can be tricky at times when loading from StoryBoard if elements are not initialised in time.

Thank you, I have implemented these changes but nothing's changed — alessionossa, Sep 16 '16 at 17:04

score 0 · Accepted Answer · answered Sep 16 '16 at 17:03

Try to implement these methods:

func beginInteractiveMovementForItem(at: IndexPath) -> Bool
func updateInteractiveMovementTargetPosition(targetPosition: CGPoint)
func endInteractiveMovement()
func cancelInteractiveMovement()

You can follow this tutorial: http://nshint.io/blog/2015/07/16/uicollectionviews-now-have-easy-reordering/

Cannot reorder Collection View cells

2 Answers2