CODEWITHSUNDEEP
iosswiftuicollectionview
hap497
hap497

Reputation: 163225

How to set collection View to nth element

I have 1 ViewController and it will launch another ViewController which has a CollectionView.

I want to set the uicollecitonView to a specified element when it first start. In previous thread someone suggests me to use ' set the contentOffset of the collection view to (collection view width) * selectedRow'. But I can't get that to work.

In my prepareForSegue function, I have added:

  x = Float(indexPath.row) * 375.0 // 375 is the width of 1 cell
  var point = CGPointMake(CGFloat(x), 0)
  println ("***x=")
  println (x)
  detailController.collectionView?.setContentOffset(point , animated: false)
where detailController is UICollectionViewController.

and in the UICollectionViewDataSource of my collection View, I always see it get the 0th element, not the nth element

override func collectionView(collectionView: UICollectionView, cellForItemAtIndexPath indexPath: NSIndexPath) -> UICollectionViewCell {
        let cell = collectionView.dequeueReusableCellWithReuseIdentifier(reuseIdentifier, forIndexPath: indexPath) as DetailViewCell

        // Configure the cell
        println("DetailViewController in cellForItemAtIndexPath()")
        println(indexPath.row)
     cell.myitem = allItems[indexPath.row]
return cell }

And I always see cellForItemAtIndexPath trying to get 0th element of the allItems (that is the whole collections of all my objects.

Any idea to solve this?

Update:

Thanks. I tried I get this exception: * Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: 'attempt to scroll to invalid index path: {length = 1, path = 4}'

I am sure I have 26 items in my list. Why there is only 1 when I want to scroll it to 4th element:

class MyViewCollectionViewController: UICollectionViewController {

    override func viewDidAppear(animated: Bool) {
            println("MyViewCollectionViewController viewDidAppear")

            println("items.count")
            println(items?.count)  // print out 26

            println(index) // print out 4

            var newIndex = NSIndexPath(index: self.index)
            self.collectionView?.scrollToItemAtIndexPath(newIndex, atScrollPosition: UICollectionViewScrollPosition.Left, animated: false)
        }
}

Upvotes: 1

Views: 3172

Answers (1)

rob mayoff
rob mayoff

Reputation: 385910

Usually a collection view uses index paths with a section and an item. Try creating newIndex this way in viewDidAppear:

let newIndex = NSIndexPath(forItem:self.index inSection:0)

Upvotes: 5

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