Question

Update: -[NSIndexPath row]: message sent to deallocated instance 0x895fe70

When I run my app on device and Analyze it says:

An Objective-C message was sent to a deallocated object (zombie) at address: 0xaa722d0.

It’s showing an error at:

- (void)tableView:(UITableView *)tableView 
didSelectRowAtIndexPath:(NSIndexPath *)indexPath {

    int newRow = [indexPath row];
    int oldRow = (lastIndexPath != nil) ? [lastIndexPath row]: -1;

---

I am very new to Objective C programming and have been struggling with the below issue since two days, I recently created an app using Xcode 3.2.6 but upgraded to Xcode 4 two days back and now facing memory deallocation issues in my below code. I researched on using instruments and enabled zombie and understood where the problem is occurring but just not able to resolve it,
I request some guidance please.. below is my code being run in Xcode 4.2.

#pragma mark -
#pragma mark Table Data Source Methods
- (NSInteger)tableView:(UITableView *)tableView 
 numberOfRowsInSection:(NSInteger)section {
    return [list count];
}
- (UITableViewCell *)tableView:(UITableView *)tableView 
         cellForRowAtIndexPath:(NSIndexPath *)indexPath {

    static NSString *CheckMarkCellIdentifier = @"CheckMarkCellIdentifier";

    UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:
                             CheckMarkCellIdentifier];
    if (cell == nil) {
        cell = [[[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault 
                                       reuseIdentifier:CheckMarkCellIdentifier] autorelease];
    }
    NSUInteger row = [indexPath row];
    NSUInteger oldRow = [lastIndexPath row];
    cell.textLabel.text = [list objectAtIndex:row];
    cell.accessoryType = (row == oldRow && lastIndexPath != nil) ? 
    UITableViewCellAccessoryCheckmark : UITableViewCellAccessoryNone;

    return cell;
}

#pragma mark -
#pragma mark Table Delegate Methods
- (void)tableView:(UITableView *)tableView 
didSelectRowAtIndexPath:(NSIndexPath *)indexPath {

    int newRow = [indexPath row];
    int oldRow = (lastIndexPath != nil) ? [lastIndexPath row]: -1;

    //----Captures the value selected in the list and shown in parent view.
    UITableViewCell *cell = [tableView cellForRowAtIndexPath:indexPath];
    SchneiderBMSAppDelegate *appDelegate = (SchneiderBMSAppDelegate *)[[UIApplication sharedApplication] delegate];
    appDelegate.priorityValue = cell.textLabel.text;

    NSLog(@"Product selected is: %@",appDelegate.priorityValue);

    if (newRow != oldRow)
    {
        UITableViewCell *newCell = [tableView cellForRowAtIndexPath:
                                    indexPath];
        newCell.accessoryType = UITableViewCellAccessoryCheckmark;

        UITableViewCell *oldCell = [tableView cellForRowAtIndexPath: 
                                    lastIndexPath]; 
        oldCell.accessoryType = UITableViewCellAccessoryNone;
        lastIndexPath = indexPath;

    }

    [tableView deselectRowAtIndexPath:indexPath animated:YES];
}

- (void)viewDidUnload {
    self.list = nil;
    self.lastIndexPath = nil;
    [super viewDidUnload];
}
- (void)dealloc {
   [list release];
    [lastIndexPath release];
    [super dealloc];
}

Answer 1

You seem to be assuming that when lastIndexPath is released, it will become nil. That isn’t so. You either need to retain the object (preferably by using a setter rather than setting the instance variable directly) or not store a reference to it.