there is 0.4 ms latency between datasource delegate numberOfItemsInSection and itemsAtRow methods , so if any background thread changes the rxbehavioralrelay it will call collectionView.reloadData() on main thread but it goes down continue executing if done for several times because pf sync issue of brelay.
//55225 - 54823 = 402 microsecond / 0.4ms in iphone 14 pro simulator
class MyCollectionViewDataSource: NSObject, UICollectionViewDataSource {
let data :[String]? = nil
func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
print("point1")
let count = crashvm.shared.productList.value.count
//fix for this issue is >
//DispatchQueue.main.async {
crashvm.shared.productList.accept(
[Product(name: "name", price: 10, description: "asd"),
Product(name: "name1", price: 11, description: "asd1"),
Product(name: "name2", price: 12, description: "asd2"),
Product(name: "name3", price: 13, description: "asd3"),Product(name: "name33", price: 13, description: "asd3")]
)
// }
return count
}
another way to crash
func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
printMachineTimeInMicroseconds(inn:"cellForItemAt") //55225 - 54823 = 402 microsecond / 0.4ms in iphone 14 pro simulator
DispatchQueue.global(qos: .background).asyncAfter(deadline: DispatchTime.now() + 1) {
//this puts into the main queue so resolves the issue ->
//DispatchQueue.main.async {
crashvm.shared.productList.accept(
[Product(name: "2name", price: 10, description: "asd"),
Product(name: "name", price: 10, description: "asd"),
Product(name: "name", price: 10, description: "asd")]
)
// }
}
// Always use the correct method to dequeue the cell
guard let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "CellReuseIdentifier", for: indexPath) as? MyCollectionViewCell, let data:Product = crashvm.shared.productList.value[safe: indexPath.row] else {
return UICollectionViewCell()
}2023-07-22 17:44:47.944362+0300 test123[4206:4954563] *** Assertion failure in -[UICollectionView _createPreparedCellForItemAtIndexPath:withLayoutAttributes:applyAttributes:isFocused:notify:], UICollectionView.m:3390
2023-07-22 17:44:47.975588+0300 test123[4206:4954563] *** Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason: 'the cell returned from -collectionView:cellForItemAtIndexPath: does not have a reuseIdentifier - cells must be retrieved by calling -dequeueReusableCellWithReuseIdentifier:forIndexPath:'
*** First throw call stack:
(
0 CoreFoundation 0x0000000180437330 __exceptionPreprocess + 172
1 libobjc.A.dylib 0x0000000180051274 objc_exception_throw + 56
2 Foundation 0x0000000180ae29b4 _userInfoForFileAndLine + 0
3 UIKitCore 0x00000001095077d0 -[UICollectionView _createPreparedCellForItemAtIndexPath:withLayoutAttributes:applyAttributes:isFocused:notify:] + 2292
4 UIKitCore 0x000000010950f7c4 -[UICollectionView _createVisibleViewsForSingleCategoryAttributes:limitCreation:fadeForBoundsChange:] + 1064
5 UIKitCore 0x000000010950fad4 -[UICollectionView _createVisibleViewsForAttributes:fadeForBoundsChange:notifyLayoutForVisibleCellsPass:] + 276
6 UIKitCore 0x000000010950e1d0 -[UICollectionView _updateVisibleCellsNow:] + 1612
7 UIKitCore 0x0000000109513134 -[UICollectionView layoutSubviews] + 300
8 UIKitCore 0x000000010a1bac00 -[UIView(CALayerDelegate) layoutSublayersOfLayer:] + 1860
9 QuartzCore 0x0000000187dfd528 _ZN2CA5Layer16layout_if_neededEPNS_11TransactionE + 440
10 QuartzCore 0x0000000187e08288 _ZN2CA5Layer28layout_and_display_if_neededEPNS_11TransactionE + 128
11 QuartzCore 0x0000000187d32130 _ZN2CA7Context18commit_transactionEPNS_11TransactionEdPd + 440
12 QuartzCore 0x0000000187d5d0f4 _ZN2CA11Transaction6commitEv + 636
13 QuartzCore 0x0000000187d5e518 _ZN2CA11Transaction25flush_as_runloop_observerEb + 68
14 CoreFoundation 0x0000000180399c10 __CFRUNLOOP_IS_CALLING_OUT_TO_AN_OBSERVER_CALLBACK_FUNCTION__ + 32
15 CoreFoundation 0x000000018039457c __CFRunLoopDoObservers + 512
16 CoreFoundation 0x0000000180394a20 __CFRunLoopRun + 948
17 CoreFoundation 0x0000000180394254 CFRunLoopRunSpecific + 584
18 GraphicsServices 0x0000000188eb7c9c GSEventRunModal + 160
19 UIKitCore 0x0000000109d16ff0 -[UIApplication _run] + 868
20 UIKitCore 0x0000000109d1af3c UIApplicationMain + 124
21 libswiftUIKit.dylib 0x0000000102d78454 $s5UIKit17UIApplicationMainys5Int32VAD_SpySpys4Int8VGGSgSSSgAJtF + 100
22 test123 0x0000000102213c50 $sSo21UIApplicationDelegateP5UIKitE4mainyyFZ + 120
23 test123 0x0000000102213bc8 $s7test12311AppDelegateC5$mainyyFZ + 44
24 test123 0x0000000102213ccc main + 28
25 dyld 0x00000001026a9514 start_sim + 20
26 ??? 0x0000000102775f28 0x0 + 4336344872
27 ??? 0x1750000000000000 0x0 + 1679842661009195008
)
libc++abi: terminating due to uncaught exception of type NSException
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