Uicollectionview Update a Single Cell

Updating a single cell in swift UICollectionview

The cellForItemAt method is what updates your cells. The proper way to get a cell to update is to update the model, then reload the collection view, which will call cellForItemAt and redraw your cell based on the model.

In your case it looks like your model is self.lettersArray0 so make sure it has been updated before you call reload.

You can reload your cells using any of the following methods:

    collectionView?.reloadData()
    collectionView?.reloadItems(at: )
    collectionView?.reloadSections(sections:)

UICollectionView update a single cell

- (void)reloadItemsAtIndexPaths:(NSArray *)indexPaths

Here it is a method to reload the specific indexPaths in your collectionView

How to reload only one cell in a collectionView?

The problem with the lag in the collectionView can be the way tha you use NSData, consider use Alamofire Image, like this

if imageUrl.count > 0 {
        let eachImage = imageUrl[indexPath.row]
        Alamofire.request(eachImage).responseImage(completionHandler: {(response) in
            print("answer\(response)")
            if let image = response.result.value{
                DispatchQueue.main.async {
                    cell.ImageView.image = image
                }
            }
        })
        }

iOS: reload single cell of UICollectionView

It depends on your implementation and how you have grouped your cells into sections but let's assume you have one section and each element in your array corresponds to a row in your table.

If you wanted to reload a cell corresponding to an array element at index x all you need to do is write

[_collectionView performBatchUpdates:^{
    [_collectionView reloadItemsAtIndexPaths:@[[NSIndexPath x inSection:0]]];
} completion:^(BOOL finished) {}];

Conversely, if you have the cell but want to find its index path you can always call [collectionView indexPathForCell:myCell]

How to update UICollectionView with another array when click on cell?

I have an example for you. Hope it will help you

var arr : [String] = []

var collectionView:UICollectionView!

override func viewDidLoad()
{
    super.viewDidLoad()

    arr = ["ONE","TWO","THREE"]
}

func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath)
{
   if indexPath.row == 1
   {
       arr = ["ABC", "EFG", "HIJ"]
       collectionView.reloadData()
   }
   else if indexPath.row == 2
   {
       arr = ["1", "2", "3"]
       collectionView.reloadData()
   }
}

Xcode reload just one cell in UiCollectionView

Use the method called reloadItemsAtIndexPaths:

[self.collectionView reloadItemsAtIndexPaths:@[indexPathOfYourCell]];

UICollectionView - How to update all cells with change from one cell

Clear new cells:

Since I am not understanding your question to a 100%, I assume that your problem is that new cells get the value of cell_1, which is not something you want.

If that is the case, then there is a function called prepareForReuse in UICollectionViewCell.
In your subclass of the UICollectionViewCell, implement the following:

override func prepareForReuse() {
    super.prepareForReuse()
    textfield.text = ""
}

That should do the trick, given that your textfield is called textfield.

Performs any clean up necessary to prepare the view for use again.
https://developer.apple.com/reference/uikit/uicollectionreusableview/1620141-prepareforreuse

Update all cells:

If your question is how to update other cells to get the same content as cell_1, then this means that the Collection View subclass needs to know about an update in cell_1 and then transform that update to the other cells.
One way of doing that is having your textfields delegate set in the Collection View. When the value is changed (textField(_:shouldChangeCharactersIn:replacementString:)), get all the visible cells and update those textfields accordingly. Maybe also save either a reference to the textfield in cell_1, or a string variable in your Collection View stating the latest entered value so you can update cells as they get rendered.
You don't want to use reloadData() though, since that will remove the focus from the textField, since the textField is reloaded.

Solution:

class ViewController: UIViewController {
    @IBOutlet weak var collectionView: UICollectionView!

    fileprivate var customString: String?
}

extension ViewController: UICollectionViewDataSource {

    func numberOfSections(in collectionView: UICollectionView) -> Int {
        return 1
    }

    func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
        return 5
    }

    func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
        let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "CustomCell", for: indexPath) as! CustomCell

        cell.textField.delegate = self
        cell.textField.text = customString

        return cell
    }

}

extension ViewController: UITextFieldDelegate {

    func textField(_ textField: UITextField, shouldChangeCharactersIn range: NSRange, replacementString string: String) -> Bool {

        customString = string

        for cell in collectionView.visibleCells {
            if let cell = cell as? CustomCell,
                let text = textField.text,
                cell.textField != textField {
                cell.textField.text = text+string
            }
        }

        return true
    }

}

The only con in the code above is that it loops through cells that currently are visible. Usually I'd recommend to stay out of looping unless absolutely necessary, but the alternative to the solution above would be to post a notification and having the cells listen to that notification and update its content accordingly. Doing that would not only be overkill, but also something notifications aren't really meant for. Third option would be to hold a weak reference in an array to every textfield, which might not be optimal as well since it creates unnecessary overhead. After all visibleCells already is an array of the cells currently visible which each hold a reference to an UITextField.

Can UICollectionViewUpdateItem be used to update a single label?

If you know the index path of the cell you want to update, you can get the cell using cellForItem(at: IndexPath). From there you can edit your cell's label.

However, I suggest you don't change your underlying data so that it's in a state that is unsuitable for presentation in the UI. The collection view can decide to create cells at times that are unpredictable to you.

UICollectionViewUpdateItem is used to indicate e.g. from where a cell moved, and where it moved to, or that a cell at a certain position was deleted, updated, etc. The docs state:

You do not create instances of this class directly.

So it means you should only create it indirectly, for example through reloadItems(at: [IndexPath]). It will reload your entire cell and should not be used to update a single detail of it.

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