ReloadTable crashes app - iphone

Question

This code causes the app to crash! I'm looping through a dictionary and everything logs out fine. It works when i write -1 in the for loop but not otherwise,
-(void)updateProjectTimes {
for(int i = 0; i < [projectsTable numberOfRowsInSection:0]-1; i++) {
NSString *currentValue = [[[projects objectForKey:#"activeProjects"] objectAtIndex:i] objectForKey:#"timepassed"];
NSString *finishValue = [[[projects objectForKey:#"activeProjects"] objectAtIndex:i] objectForKey:#"timeleft"];
if([currentValue intValue] < [finishValue intValue]) {
[[[projects objectForKey:#"activeProjects"] objectAtIndex:i] setObject:[NSString stringWithFormat:#"%d", ([currentValue intValue] + 1)] forKey:#"timepassed"];
} else {
[(NSMutableArray *)[projects objectForKey:#"activeProjects"] removeObjectAtIndex:i];
if([[projects objectForKey:#"activeProjects"] count] == 0) {
[projectTimer invalidate];
projectTimer = nil;
}
}
//[projectsTable reloadData]; works if i put it here!
}
[projectsTable reloadData]; //<- But not here!! :(
}

Answer 1

I assume you are wokring with tableView. Apparently you are modifing the data source of your tableView. When you remove an object from the data source, you have to adjust your tableView as well. Meaning either call reloadData, or call [tableView deleteRowsAtIndexPaths:(NSArray *)indexPaths withRowAnimation:(UITableViewRowAnimation)animation].
The reason your app doesn't crash if you put -1, could be -- perhaps -- because there is only on item that matches the [currentValue intValue] < [finishValue intValue] condition, so that if you go through [projectsTable numberOfRowsInSection:0]-1, after removing that object, numberOfRowsInSection matches the count of projectsTable.
But it is good only for one cycle. When the next cycle happens, in the if...loop, you app crashes again, unless you include the [projectsTable reloadData] in the same if...loop.
While the reloadData method works just fine, but if you are simply removing a row, or adding a row to your table by adding or removing objects, its better to use deleteRowsAtIndexPaths or insertRowsAtIndexPaths methods. There will be less overhead and work for your app, and would make it smoother and faster.
The bottom line, to make your code work, right after [(NSMutableArray *)[projects objectForKey:#"activeProjects"] removeObjectAtIndex:i]; remove the corresponding object from your tableView by calling deleteRowsAtIndexPaths.
Alternatively, you can also use beginUpdates and endUpdates. For a complete reference, refer to http://developer.apple.com/library/ios/#documentation/uikit/reference/UITableView_Class/Reference/Reference.html
Hope it helps.