How to get index of every item in an array Objective-C

Question

For an iPhone app I am developing I need to assign custom uitableviewcell images based on the integers of arbitrary items in an array. I noticed while doing some testing that indexPath of row only returns indices for the view shown, so basically I need to know how to take an array, of arbitrary size, let's say right now it has 10 items, and those 10 items are in a table, each item a cell, I need each item to have an index like item 1 is index 0, item 2 is index 1 and so on. So my code would read, if the index == 0, then display this image in the cell, if the index != 0 then display another. I tried that but like I said if I scrolled to the bottom of my tableview it would reassign whichever table item is at the top of the view to 0, so as I scrolled the images kept changing. So basically i need help assigning the images based on an index in my array rather than on the index of the table.

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {    

    static NSString *MyIdentifier = @"MyIdentifier";

    UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:MyIdentifier];
    if (cell == nil) {  
        cell = [[[UITableViewCell alloc] initWithStyle:UITableViewCellStyleSubtitle reuseIdentifier:MyIdentifier] autorelease];  
    }

    cell.detailTextLabel.lineBreakMode = UILineBreakModeWordWrap;
    cell.detailTextLabel.numberOfLines = 1;
    cell.accessoryType =  UITableViewCellAccessoryDisclosureIndicator;

    NSString *title =[[stories objectAtIndex: indexPath.row] objectForKey: @"summary"];
    NSString *title2 =[[stories objectAtIndex: indexPath.row] objectForKey: @"title"];
    NSString *dayOfMonthString = [title substringWithRange: NSMakeRange(2, 2)];
    int dateChooser = [dayOfMonthString intValue];

    NSString *monthString = [title substringWithRange: NSMakeRange(0, 2)];

    int monthChooser = [monthString intValue];
    cell.textLabel.text =title2;


    cell.imageView.image = 
    [UIImage imageNamed: [NSString stringWithFormat: @"cal%d.png", dateChooser]];

    if (monthChooser == 1 && (INDEX COMPARISON CODE???){
        UIImageView *myImageView = [[UIImageView alloc] initWithImage:[UIImage imageNamed:@"Jan1.png"]];
        [cell setBackgroundView:myImageView];
    }

Do us a favor and post your code, please. Not all of it, just the relevant bits. — PengOne
– PengOne, Commented Sep 7, 2011 at 21:06
May I suggest this post: stackoverflow.com/questions/1135075/… — Daniel
– Daniel, Commented Sep 7, 2011 at 21:09
That post doesn't really apply because I need the index of every item in the array no matter the size, not the index of a single object in the array — Matt
– Matt, Commented Sep 7, 2011 at 22:39

AliSoftware · Accepted Answer · 2011-09-07 21:28:01Z

4

Your problem is not getting the right index for the right cell. The row property of the indexPath do correspond to the index of the cell in the whole list of cells, not the index of the visible cells only, so exactly as you expected initially.

I bet your problem is that you don't use the reuse mechanism of UITableViewCells correctly . When you scroll in your TableView, UITableViewCells that are not on screen anymore are "recycled" and reused to display new cells onscreen, in order to avoid too much allocations and useless initializations that would else slow down the scrolling of your tableView.

The correct code pattern for returning a cell is the following:

-(UITableViewCell*)tableView:(UITableView*)tableView cellForRowAtIndexPath:(NSIndexPath*)indexPath
{
    // Try to retrieve a previously created cell that is not used anymore
    // That's the "recycling" part, we try to reuse a cell instead of creating a new one if possible
    UITableViewCell* cell = [tableView dequeueCellWithIdentifier:@"myIdentifier"];

    if (cell == nil)
    {
        // We failed to recycle a previously created cell, so we have no choice to allocate a new one
        cell = [[[UITableViewCell alloc] initWithStyle:... reuseIdentifier:@"myIdentifier"] autorelase];
        // As we just created the cell, we configure everything that will be common to every cell
        // and that won't change even if the cell is reused later when you scroll

        // e.g. text color, text font, accessoryType, ...
        cell.textLabel.textColor = [UIColor blueColor];
        ...
    }

    // Now we got here either with a brand new cell that have just been created…
    // … or after reusing an old cell that were not onscreen and has been recycled
    // So THIS IS THE PLACE to configure everything that is SPECIFIC to each cell

    // namely cell text, especially
    cell.textLabel.text = [yourDataArray objectAtIndex: indexPath.row];


    return cell;
}

edited Sep 7, 2011 at 21:28

answered Sep 7, 2011 at 21:08

AliSoftware

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3 Comments

Matt Over a year ago

I updated my question with my current code. Don't worry about the date chooser or anything, all of that works and is only relevant for one of the if conditions.

AliSoftware Over a year ago

As explained in my answer, if you have a condition in the part that is common to reused and newly allocated cells (the part after the if (cell == nil)), then you need to take into account that your cell will be reused when you scroll. Especially you have an if (monthChooser == 1 && (INDEX COMPARISON CODE???) (of course use indexPath.row for your index comparison that's not the problem, as explained!) that changes your cell backgroundView, don't forget to implement the else cell.backgroundView = nil so that when your cell is reused you restore the standard state!

AliSoftware Over a year ago

And do move your numberOfLines, accessoryType and lineBreakMode affectation inside your if (cell == nil) too, also as explained in my answer!!

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