Question

I have a UITableView in an iPhone application which I am refreshing (by calling [self.tableView reloadData] in the action method for a UISegmentedControl dynamically embedded in one of the UITableView cells. The table view is refreshed to update a text value for one of the cells.

However, the following code seems to produce an unwanted side-effect. It appears that each time the UITableView refreshes it creates a new instance of the UISegmentedControl (and possibly the images – I’m not sure) over the existing one(s).

The only reason I notice this is that with each refresh a barely perceptible border starts to form around the UISegmentedControl and the application slows noticeably. I would be extremely grateful for any suggestions/code-solutions to my current predicament.

// Customize the appearance of table view cells.
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {

    static NSString *CellIdentifier = @"Cell";


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

    NSUInteger section = indexPath.section;
    NSUInteger row = indexPath.row;

    // Set up the cell...       


    //populates the personal info section
    if (section == kPersonalInfoAddSection) {

        if (row == kNameRow) {

                    //Other code irrelevant to this question was removed for the sake of clarity
        }
        else if(row == kHeightRow) {

            cell.imageView.image = [UIImage imageNamed:@"tableview_height_label.png"];
                    //THIS IS THE TEXT I'M TRYING TO UPDATE
            cell.textLabel.text = [Formatter formatHeightValue:mainUser.heightInMM forZone:self.heightZone];
            cell.detailTextLabel.text = REQUIRED_STRING;

        }
    }

    //populates the units section
    if (section == kUnitsSection) {

        if (row == kHeightUnitsRow) {
            NSArray *heightUnitsSegments = [[NSArray alloc] initWithObjects:FT_AND_IN_STRING, M_AND_CM_STRING, nil];

            UISegmentedControl *heightUnitControl = [[UISegmentedControl alloc] initWithItems:heightUnitsSegments];

            CGRect segmentRect = CGRectMake(90, 7, 200, 30);
            [heightUnitControl setFrame:segmentRect];
            //[heightUnitControl setSelectedSegmentIndex:0];
            [heightUnitControl addTarget:self action:@selector(heightSegmentClicked:) forControlEvents:UIControlEventValueChanged];
            heightUnitControl.tag = kHeightSegmentedControlTag;

            cell.textLabel.text = @"Height:";
            cell.detailTextLabel.text = @"(units)";
            [cell.contentView addSubview:heightUnitControl];

            [heightUnitsSegments release];
            [heightUnitControl release];

        }
        else if(row == kWeightUnitsRow) {

                    //Other code irrelevant to this question was removed for the sake of clarity    

        }
    }

    return cell;
}

Thank you all in advance!

Answer 1

You’re right, it is creating a new instance of the UISegmentedControl. It’s because you are using a generic cell identifier, @”Cell”, then adding the UISegmentedControl each time, never removing it. The cells get cached containing the UISegmentedControl, you retrieve the cached cell and add the control again.

You could use a more specific cell identifier and if cell != nil you know it contains the UISegmentedControl already. Or create a new cell each time that way you’re not using a cached cell that already contains the control.

With the image view you just set the cells image view property without adding a new view to the cell so that one is ok, it gets replaced each time.

Since the text you are trying to update doesn’t have to do with the UISegmentedControl I think you should be able to use a more specific cell identifier and add the control only on cell creation.