Question

I have an application with navigation controller and some table view controller. In table view controller I have a two section header my definitions:

- (UIView *)tableView:(UITableView *)tableView viewForHeaderInSection:(NSInteger)section
{

  if (section == 0) {

   UIView* customView = [[UIView alloc] initWithFrame:CGRectMake(0, 0, tableView.bounds.size.width, 74)];

        UIImageView *myImageView = [[UIImageView alloc] initWithImage:[UIImage imageNamed:@"toolbarTopBack.png"]];

        UILabel *headline = [[UILabel alloc] initWithFrame:CGRectMake(11, 14, 305, 21)];
        headline.backgroundColor = [UIColor clearColor];
        headline.textColor = [UIColor whiteColor];
        headline.font = [UIFont fontWithName:@"Helvetica Neue" size:21];
        headline.text = searchPosition;

        UILabel *subHeadline = [[UILabel alloc] initWithFrame:CGRectMake(11, 36, 305, 21)];
        subHeadline.backgroundColor = [UIColor clearColor];
        subHeadline.textColor = [UIColor grayColor];
        subHeadline.font = [UIFont fontWithName:@"Helvetica Neue" size:16];
        subHeadline.text = searchRegion;

        [customView addSubview:myImageView];
        [customView addSubview:headline];
        [customView addSubview:subHeadline];


        return customView;

    } else {

        // create the parent view that will hold header Label
        UIView *customView = [[UIView alloc] initWithFrame:CGRectMake(0, 0, tableView.bounds.size.width, 44)];
        customView.userInteractionEnabled = YES;

        UIImageView *myImageView = [[UIImageView alloc] initWithImage:[UIImage imageNamed:@"mainToolBar.png"]];

        UIToolbar *topToolbar = [[UIToolbar alloc] initWithFrame:CGRectMake(0, 0, tableView.bounds.size.width, 44)];
        topToolbar.barStyle = UIBarStyleDefault;
        [topToolbar setBackgroundColor:[UIColor clearColor]];

        static dispatch_once_t onceToken; dispatch_once(&onceToken, ^{

        NSMutableDictionary *appSettingsData = [[NSMutableDictionary alloc] initWithDictionary:[appDelegate getAppStrings]];

        NSArray *segmentItems = [NSArray arrayWithObjects:[NSString stringWithFormat:@"%@ (%d)", [appSettingsData valueForKey:@"segmentButton4"], listCountOffers], [NSString stringWithFormat:@"%@ (%d)", [appSettingsData valueForKey:@"segmentButton5"], [[appDelegate comunication] getSimilarCount:[appDelegate getCurrentCI] idPosition:idPosition idRegion:idRegion]], nil];

        segmentControl = [[UISegmentedControl alloc] initWithItems:segmentItems];
        segmentControl.frame = CGRectMake(6, 8, 308, 29);
        segmentControl.autoresizingMask = UIViewAutoresizingFlexibleWidth;
        segmentControl.segmentedControlStyle = UISegmentedControlStyleBar;
        [segmentControl setTintColor:[UIColor grayColor]];
        [segmentControl addTarget:self action:@selector(segmentedControlIndexChanged:) forControlEvents:UIControlEventValueChanged];
        segmentControl.momentary = NO;
        segmentControl.selectedSegmentIndex = 0;

        });

        UIBarButtonItem *toolbarItem = [[UIBarButtonItem alloc] initWithCustomView:segmentControl];
        [topToolbar addSubview:toolbarItem.customView];

        [customView addSubview:myImageView];
        [customView addSubview:topToolbar];

        return customView;

    }

}

I use “static dispatch_once_t onceToken; dispatch_once(&onceToken, ^{“, because I need create this header only first time (because when I scroll table, method is call and call … and this is wrong) …
Everything works fine, when I create table view controller it show a headers, when I scroll it, nothing is recreating (it is fine), but when I push back button a then reopen tableview controller headers are empty. Where is problem ? Is there any solution, how to fix it ? Thanks a lot

Answer 1

You’re using dispatch_once without really needing to. The block will only be executed once, even if you subsequently remove the view controller from memory and deallocate segmentControl.

Use lazy loading instead – create a property for your segmentControl view within your view controller, and in the accessor for that, if the backing ivar is nil, create it then:

Your synthesize statement:

@synthesize segmentControl = _segmentControl

Your accessor method:

-(UISegmentedControl*)segmentControl
{
    if (_segmentControl)
        return _segmentControl;

    UISegmentedControl *segmentControl = //... create your control here 
    self.segmentControl = segmentControl
    return segmentControl;
}

Then when you want to use the view, use self.segmentControl. The first time you call it, it will be created, the subsequent times, it will be re-used.