reloadRowsAtIndexPaths:withRowAnimation: crashes my app

Question

I got a strange problem with my UITableView: I use reloadRowsAtIndexPaths:withRowAnimation: to reload some specific rows, but the app crashes with an seemingly unre

Answer 1

I had this problem which was being caused by a block calling reloadRowsAtIndexPaths:withRowAnimation: and a parallel thread calling reloadData. The crash was due to reloadRowsAtIndexPaths:withRowAnimation finding an empty table even though I'd sanity checked numberOfRowsInSection & numberOfSections.

I took the attitude that I don't really care if it causes an exception. A visual corruption I could live with as a user of the App than have the whole app crash out.

Here's my solution to this which I'm happy to share and would welcome constructive criticism. If there's a better solution I'm keen to hear it?

- (void) safeCellUpdate: (NSUInteger) section withRow : (NSUInteger) row {
    // It's important to invoke reloadRowsAtIndexPaths implementation on main thread, as it wont work on non-UI thread
    dispatch_async(dispatch_get_main_queue(), ^{
        NSUInteger lastSection = [self.tableView numberOfSections];
        if (lastSection == 0) {
            return;
        }
        lastSection -= 1;
        if (section > lastSection) {
            return;
        }
        NSUInteger lastRowNumber = [self.tableView numberOfRowsInSection:section];
        if (lastRowNumber == 0) {
            return;
        }
        lastRowNumber -= 1;
        if (row > lastRowNumber) {
            return;
        }
        NSIndexPath *indexPath = [NSIndexPath indexPathForRow:row inSection:section];
        @try {
            if ([[self.tableView indexPathsForVisibleRows] indexOfObject:indexPath] == NSNotFound) {
                // Cells not visible can be ignored
                return;
            }
            [self.tableView reloadRowsAtIndexPaths:@[indexPath] withRowAnimation:UITableViewRowAnimationNone];
        }

        @catch ( NSException *e ) {
            // Don't really care if it doesn't work.
            // It's just to refresh the view and if an exception occurs it's most likely that that is what's happening in parallel.
            // Nothing needs done
            return;
        }
    });
}