Adding sections to tableview, index out of bounds error

Question

In this app, I download data from Parse. That data is a list of 5 Messages, each with a category. There are 4 different categories as two of the messages have the same category. I want to put that data into sections on a tableview. Since the data is not ready for sectioning, I had to create 2 mutable arrays that act like index look ups. (followed this guide: https://parse.com/questions/using-pfquerytableviewcontroller-for-uitableview-sections)

Problem: I'm getting this error: -[__NSArrayM objectAtIndex:]: index 8 beyond bounds [0 .. 4]'

Question is, why am I getting this error and how do I fix it?

I've located the exact line that is the problem. First, here is what you need.

1st Mutable Dictionary: self.sectionToCategoryMap //This property maps the sections titles to the row indeces for the data. The output it looks like this: (read as, get the 1st category header from object at index 0)

0 = "Section Header 1"; 
24 = "Section Header 2";
16 = "Section Header 3";
32 = "Section Header 4";

2nd Mutable Dictionary: self.sections // This maps what items are in what section(category). Output looks like this:

"category 1" =(32);
"category 2" =(24);
"category 3" =(16);
"category 4" =(0,8);

These two Dictionaries are created by this code:

- (void)prepSections:(id)array {
    [self.sections removeAllObjects];
    [self.sectionToCategoryMap removeAllObjects];
    self.sections = [NSMutableDictionary dictionary];
    self.sectionToCategoryMap = [NSMutableDictionary dictionary];

    NSInteger *section = 0;
    NSInteger *rowIndex = 0;
    for (MessageItem  *messageItem in self.messageList) {
        NSString *category = [messageItem valueForKey:@"messageCategory"]; //retrieves category for each message -1st regulator
        NSMutableArray *objectsInSection = [self.sections objectForKey:category]; //assigns objectsinsection value of sections for current category
        if (!objectsInSection) {
             objectsInSection = [NSMutableArray array];
            // this is the first time we see this category - increment the section index
            //literally it ends up (0:Regulatory)
            [self.sectionToCategoryMap setObject:category forKey:[NSNumber numberWithInt:rowIndex]];
            section++;
        }
        [objectsInSection addObject:[NSNumber numberWithInt:(int)rowIndex++]]; //adds message to objects in section
        [self.sections setObject:objectsInSection forKey:category]; //adds dict of objects for category
    }
}

The error is happening in my in cellForRowAtIndexPath below, specifically the line: NSNumber *rowIndex = [rowIndecesInSection objectAtIndex:indexPath.row]; (note: categoryForSection is a helper method I defined, its implementation is also below.)

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {
    MessageTableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:@"Cell" forIndexPath:indexPath];

    NSString *category= [self categoryForSection:indexPath.section];
    NSArray *rowIndecesInSection = [self.sections objectForKey:category];
    NSNumber *rowIndex = [rowIndecesInSection objectAtIndex:indexPath.row]; //pulling the row indece from array above
    //gets to 3 and breaks!!!

    messageItem = [self.messageList objectAtIndex:[rowIndex intValue]];
    [cell configMessageCell:messageItem indexPath:indexPath];
    return cell;
}

For good measure, here is the rest of my code.

- (NSString *) categoryForSection:(NSInteger*)section { //takes section # and returns name of section.
    return [self.sectionToCategoryMap objectForKey:[NSNumber numberWithInt:(int)section]];
}

- (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView {
    return (unsigned long)self.sections.allKeys.count;
}

- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section {
    NSString *category = [self categoryForSection:section];
    NSArray *rowIndecesInSection = [self.sections objectForKey:category];
    return [rowIndecesInSection count];
}

- (NSString *)tableView:(UITableView *)tableView titleForHeaderInSection:(NSInteger)section {
    NSString *category =[self categoryForSection:section];
    return category;
}

Please help me fix this. It has had me stuck for days! Thank you! Matt

Answer 1

I think the problem lies in declaring these as pointers:

NSInteger *section = 0;
NSInteger *rowIndex = 0;

(Note the weird multiples of 8 in the numbers in your dictionaries - that's because pointer arithmetic works differently from "normal" arithmetic). Try with

NSInteger section = 0;
NSInteger rowIndex = 0;