Question

Just a quick question really:

I’m running a method to pull records from an sqlite database into an array, then assigning the contents of that array to an instance variable.

@interface {
NSArray *items;
}

@implementation
// The population method.
-(void)populateInstanceVariable
{
    NSMutableArray *itemsFromDatabase = [[NSMutableArray alloc] init];        

    // Sqlite code here, instantiating a model class, assigning values to the instance variables, and adding this to the itemsFromDatabase Array.


    self.items = itemsFromDatabase;
    [itemsFromDatabase release];

}
// viewDidLoad is calling the method above
-(void)viewDidLoad
{
    [self populateInstanceVariable];
    [super viewDidLoad];
}

// TableViewDataSource method - cellforIndexPath
- (UITableViewCell *)tableView:(UITableView *)passedInTableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
    UITableViewCell *cell = [[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault];

    // Load in my model from the instance variable - ***1
    MyDataModel *model = [items objectAtIndexPath:indexPath.row];

    // Assign the title to the cell from the model data
    cell.textLabel.text = model.title;

    // This is the part i'm stuck on, releasing here causes a crash!
    [model release];

    return cell;

}

@end

My question is two fold:

1. Is what i’m doing to assign data to the instance variable right? and am i managing the memory correctly?
2. How do i manage the memory for that model item in the tableview datasource? the only way i seem to be able to get it to run smoothly is if i don’t release the *model object at all, but that causes leaks surely?

Cheers.

Answer 1

No, you’re not managing memory correctly here:

• you should use “reusable” UITableViewCells, most UITableView examples show how to do this, and

• do not do [model release], you do not “own” the object in this case, you’re just referring to it so you must not release it

Here’s the typical cellForRowAtIndexPath:

-(UITableViewCell *) tableView:(UITableView *)atableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {
    static NSString *CellIdentifier = @"CellIdentifier";

    // Dequeue or create a cell of the appropriate type.
    UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier];
    if (cell == nil) 
    {
        cell = [[[UITableViewCell alloc] initWithStyle:UITableViewCellStyleValue1 reuseIdentifier:CellIdentifier] autorelease];
        // settings that do not change with every row
        cell.selectionStyle = UITableViewCellSelectionStyleGray;
    }
    // settings that change with every row
    cell.textLabel.text = @"fill in your label here";
    return cell;
}

Also, if you’re using a DB for your data, you may want to look in to Core Data, Apple’s data persistence/management framework, it includes the ability to hook aspects of your data entities directly up to UITableViews.