CODEWITHSUNDEEP
iosswiftuicollectionview
Mohamed ALOUANE
Mohamed ALOUANE

Reputation: 5407

'attempt to scroll to invalid index path: {length = 2, path = 0 - 4}

I have a horizontal collection view working as a pager of 4 screens/steps. I disabled the horizontal scrolling as a way to perform next action only from a floating button:

let nextItem = self.selectedIndexPath.item + 1
self.scrollToStep(index: IndexPath(item: nextItem, section: 0))

func scrollToStep(index: IndexPath){
   selectedIndexPath = index
   collectionView.scrollToItem(at: index, at: .centeredHorizontally, animated: true)  
}

The second time I tap the button the app crashes.

] * Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: 'attempt to scroll to invalid index path: {length = 2, path = 0 - 4}' * First throw call stack: ( 0 CoreFoundation 0x00000001088dd6fb __exceptionPreprocess + 331 1 libobjc.A.dylib
0x0000000107e81ac5 objc_exception_throw + 48 2 CoreFoundation
0x00000001088dd555 +[NSException raise:format:] + 197 3 UIKitCore
0x000000010b79ef93 -[UICollectionView _contentOffsetForScrollingToItemAtIndexPath:atScrollPosition:] + 212 4 UIKitCore 0x000000010b79f86b -[UICollectionView _scrollToItemAtIndexPath:atScrollPosition:animated:] + 70 5 0x0000000105238770 $s14 18ViewControllerC12scrollToStep5indexy10Foundation9IndexPathV_tF + 480 6 0x00000001052358b5 $s1 ar 010collectionF0_13cellForItemAtSo012UICollectionF4CellCSo0mF0C_10Foundation9IndexPathVtFySbcfU_ + 1701

Upvotes: 1

Views: 6966

Answers (2)

NavinBagul
NavinBagul

Reputation: 741

var staticIndex = 0

in button click action 

if staticIndex < 3 {
    var indexPath = IndexPath.init(row: staticIndex+1, section: 0)
    collectionView.scrollToItem(at: indexPath, at: .right, animated: true)
    staticIndex += 1
}

Upvotes: 2

vadian
vadian

Reputation: 285069

4 screens/steps are represented by the indices 0 - 3. The error clearly states an out-of-range error.

You have to check if nextItem reaches the end index

let nextItem = self.selectedIndexPath.item + 1
if nextItem < 4 {
   self.scrollToStep(index: IndexPath(item: nextItem, section: 0))
}

Upvotes: 3

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