The collection was mutated during the listing, UITableView

Question

I have a filter button that represents a UITableView in a popover. I have my categories and the "All" button to indicate that the filter is not present, as in iTunes.

I have an NSMutableDisctionary in my applicationDelegate class that I use to set checkboxes. When the application starts, only All is selected, everything else is canceled. What I want is when a row that is not “All” is selected, that row is selected and everything becomes inaccessible. Similarly, when All is selected, all lines with checkmarks no longer have checkmarks, and only All is selected using a checkmark (for example, when the application starts). In my UITableView didSelectRowForIndexPath :, I did this:

MyAppAppDelegate *dmgr = (MyAppAppDelegate *)[UIApplication sharedApplication].delegate; NSUInteger row = [indexPath row]; UITableViewCell *cell = [tableView cellForRowAtIndexPath:indexPath]; // All selected if (row == 0) { for (NSString *key in dmgr.CategoryDictionary) { [dmgr.CategoryDictionary setObject:[NSNumber numberWithBool:NO] forKey:key]; } [dmgr.CategoryDictionary setObject:[NSNumber numberWithBool:YES] forKey:@"All"]; } else { cell.accessoryType = UITableViewCellAccessoryCheckmark; NSString *key = [_categoriesArray objectAtIndex:row]; BOOL valueAtKey = [[dmgr.CategoryDictionary valueForKey:key] boolValue]; valueAtKey = !valueAtKey; [dmgr.CategoryDictionary setObject:[NSNumber numberWithBool:valueAtKey] forKey:key]; } 

Two questions. Firstly, I get this error when I select the first row (all):

 Terminating app due to uncaught exception 'NSGenericException', reason: '*** Collection <__NSCFDictionary: 0x597b3d0> was mutated while being enumerated. 

Where does the transfer take place? I thought, since I only select line 0, I could change other lines, not just line 0. I am not sure what to do with this here.

The second question is how do you want to update your model class? I was not sure if this was considered a good MVC. Thanks.

Answer 1

An enumeration is a for loop. You can iterate over a copy of the keys instead to avoid changing the dictionary when listing it:

 for (NSString *key in [dmgr.CategoryDictionary allKeys]) { //... }