iPhone viewForHeaderInSection - iphone

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

Well, to me it looks like it's a problem with your static dispatch.
When you push the Back button, chances are that your view holding the table view is released (I don't know your code, but I suppose it is like that), meaning all internal variables are gone - except your static dispatch, which won't be called the next time you instantiate the view. So, during the next instantiation your segmentItems will not be created, but because the view was released, they are empty. You should solve your 'only create once' problem differently, e.g. by remembering the created segmentItems in a dictionary and getting them from there if they do not exist yet.

Answer 2

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.

Answer 3

check it with breakpoint and see the process. it maybe the memory allocation problem. See this it may help you. http://www.icodeblog.com/2010/12/10/implementing-uitableview-sections-from-an-nsarray-of-nsdictionary-objects/