Open Radar

 
Summary:
Performing a sequence of insertItems, reloadData, insertItems, with an interval of 0.1s between each operation, will trigger an assert within UIKit

Steps to Reproduce:
Open and run the attached project under iOS 9.3 (last tested in the 9.3 simulator).

Briefly:
 - Create a UICollectionView with a counter for the number of items, initially zero.
 - Insert a single item with insertItemsAtIndexPaths at item index 0
 - Wait 0.1s
 - Reload the collection-view using reloadData
 - Wait 0.1s
 - Insert a second item with insertItemsAtIndexPaths at item index 1

Expected Results:
I would expect the collection view to end up with two items.

Actual Results:
An assert is triggered in the second insertItemsAtIndexPaths call, with a message like "request for index path for global index 1152930280101002667 when there are only 2 items in the collection view"

Version:
iOS 9.3.2, Xcode 7.3.1

Notes:
Replacing 'reloadData' with 'reloadSections' behaves correctly.
Increasing the delay between calls to 0.2s or higher behaves correctly.

Configuration:
iPhone Simulator, iPhone 6 

Attachments:
'CVCrasher.zip' and 'stack.txt' were successfully uploaded.



Relevant snippet from attached project:

@interface ViewController : UICollectionViewController
{
    int numItems;
}

@end

@implementation ViewController

- (void)viewDidAppear:(BOOL)animated
{
    [super viewDidAppear:animated];
    [self insert];
}

- (UICollectionViewCell*)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath {
    return [collectionView dequeueReusableCellWithReuseIdentifier:@"cell" forIndexPath:indexPath];
}

- (NSInteger)collectionView:(UICollectionView *)collectionView numberOfItemsInSection:(NSInteger)section
{
    return numItems;
}

- (void)insert
{
    numItems++;
    [self.collectionView insertItemsAtIndexPaths:@[[NSIndexPath indexPathForItem:numItems-1 inSection:0]]];

    dispatch_after(dispatch_time(DISPATCH_TIME_NOW, 100*NSEC_PER_MSEC), dispatch_get_main_queue(), ^{
        [self reload];
    });
}

- (void)reload
{
    numItems = 1;
    [self.collectionView reloadData];
    dispatch_after(dispatch_time(DISPATCH_TIME_NOW, 100*NSEC_PER_MSEC), dispatch_get_main_queue(), ^{
        [self insert];
    });
}

@end