How to show a collectionView at a Specific Index in Swift

Question

I am using a library called VegaScrollFlowLayout that is located on github. I am trying to give an exact index in my collectionView, and present the data starting from that index, but I keep getting a reset back to Index 0 and not Index 10.

 override func viewWillAppear(_ animated: Bool) {
    super.viewWillAppear(animated)


    collectionView.scrollToItem(
        at: NSIndexPath(item: 10, section: 0) as IndexPath,
        at: [],
            animated: false)
  
    
 }

Duncan C · Accepted Answer · 2020-12-23 22:54:40Z

1

You should probably put your call to scrollToItem(at:at:animated:) in viewDidAppear(), not viewWillAppear(). In viewWillAppear() the collection view has not shown any cells yet. I don't think you'd need a delay that way.

Using delays is a fragile way of doing things. Better to move the code to the correct lifecycle method.

answered Dec 23, 2020 at 22:54

Duncan C

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Chris · Accepted Answer · 2020-12-21 23:08:17Z

0

Well, after some digging around, I had to add a delay in the code.

override func viewWillAppear(_ animated: Bool) {
    super.viewWillAppear(animated)

    DispatchQueue.main.asyncAfter(deadline: .now() + 0.1)
    {
        self.collectionView.scrollToItem(
        at: NSIndexPath(item: 15, section: 0) as IndexPath,
        at: [],
            animated: false)

    }
 }

This fixed the issue.

answered Dec 21, 2020 at 23:08

Chris

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1 Comment

Duncan C Over a year ago

You should probably put your call to scrollToItem(at:at:animated:) in viewDidAppear(), not viewWillAppear(). In viewWillAppear()` the collection view has not shown any cells yet. I don't think you'd need a delay that way. (Although I haven't tested it.)

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