UICollectionView: header view programmatically [closed]

Answer 1

Typically you put this register line in the viewDidLoad or some sort of initialize so that it is not called over and over again. But mainly you have some confusion. You register a class for the header but you dequeue a class on the footer. You should register a class for both and dequeue the right one for each.

Notice your register uses UICollectionElementKindSectionHeader:

[self.collectionView registerClass:[UICollectionReusableView class] forSupplementaryViewOfKind:UICollectionElementKindSectionHeader withReuseIdentifier:@"header"];

Notice your dequeue uses UICollectionElementKindSectionFooter :

UICollectionReusableView *supplementaryView = [self.collectionView dequeueReusableSupplementaryViewOfKind:UICollectionElementKindSectionFooter withReuseIdentifier:@"header" forIndexPath:indexPath];

hope that helps.

Answer 2

why are you adding lblHeader to self.collectionView add to headerView.And return headerView.Replace your code with it

    if (kind == UICollectionElementKindSectionHeader) {
    UICollectionReusableView *headerView = [self.collectionView dequeueReusableSupplementaryViewOfKind:UICollectionElementKindSectionHeader withReuseIdentifier:nil forIndexPath:indexPath];

        self.lblHeader = [[UILabel alloc]initWithFrame:CGRectMake(120, 10, 100, 30)];
        self.lblHeader.backgroundColor = [UIColor whiteColor];
        self.lblHeader.textColor = [UIColor redColor];
        self.lblHeader.text = @"Level 1";

       // [self.collectionView addSubview:self.lblHeader];
          [headerView addSubview:self.lblHeader];

       return headerView;
}

Answer 3

try this :

    //ON top 
    static NSString *headerViewIdentifier = @"Test Header View";
    static NSString *footerViewIdentifier = @"Test Footer View";


    - (UICollectionReusableView *)collectionView:(UICollectionView *)collectionView viewForSupplementaryElementOfKind:(NSString *)kind atIndexPath:(NSIndexPath *)indexPath
    {
        NSString *identifier = nil;

        if ([kind isEqualToString:UICollectionElementKindSectionHeader]) {
            identifier = headerViewIdentifier;
        }
        else if ([kind isEqualToString:UICollectionElementKindSectionFooter]) {
            identifier = footerViewIdentifier;
        }

        // TODO Setup view

        UICollectionReusableView *supplementaryView = [collectionView dequeueReusableSupplementaryViewOfKind:UICollectionElementKindSectionFooter withReuseIdentifier:identifier forIndexPath:indexPath];

        return supplementaryView;
    }

Answer 4

The error you're seeing is pretty clear. You're trying to dequeue a reusable view but the collection view doesn't know anything about the reuse identifier you're passing.

You need to call registerClass:forSupplementaryViewOfKind:withReuseIdentifier: before dequeueReusableSupplementaryViewOfKind:withReuseIdentifier:forIndexPath: is called. I typically call one of the register methods in viewDidLoad so all the setup is done and I can just call the dequeue method. If you're loading your custom header and footer views from nib you can use the registerNib:forSupplementaryViewOfKind:withReuseIdentifier: method.

Edit

I see you updated the code. You need to move these lines

UICollectionViewFlowLayout *layout= [[UICollectionViewFlowLayout alloc]init];

self.collectionView = [[UICollectionView alloc]initWithFrame:CGRectMake(0, 0, 390, 300) collectionViewLayout:layout];

above the lines where you're calling the register class methods. You cannot send messages to an object before you allocate and initialize it.

Answer 5

If you are not displaying anything on the header then how could you expect header view to show you something on header part of UICollectionView.Try following code.This is working code

- (void)viewDidLoad
{
    arry=[[NSArray alloc] initWithObjects:@"One",@"Two",@"Three",@"Four", nil];
    [_collectionView registerClass:[UICollectionViewCell class] forCellWithReuseIdentifier:@"cellIdentifier"];
    [self.collectionView registerClass:[UICollectionReusableView class] forSupplementaryViewOfKind:UICollectionElementKindSectionHeader withReuseIdentifier:@"HeaderView"];

    // Do any additional setup after loading the view, typically from a nib.
}


    - (NSInteger)collectionView:(UICollectionView *)collectionView numberOfItemsInSection:(NSInteger)section
{
    return [arry count];
}

- (NSInteger)numberOfSectionsInCollectionView:(UICollectionView *)collectionView
{
    return 20;
}

// The cell that is returned must be retrieved from a call to -dequeueReusableCellWithReuseIdentifier:forIndexPath:
- (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath
{
    UICollectionViewCell *cell=[collectionView dequeueReusableCellWithReuseIdentifier:@"cellIdentifier" forIndexPath:indexPath];

    if (cell==nil) {
        cell=[[UICollectionViewCell alloc] init];
    }

    UILabel *label = (UILabel*)[cell.contentView viewWithTag:21];

    if (label==nil) {
      label=[[UILabel alloc] initWithFrame:CGRectMake(0, 0, 60, 60)];
      label.tag = 21;
      [cell.contentView addSubview:label];
    } 

    label.text = [arry objectAtIndex:indexPath.row];

    NSLog(@"cell is %@",NSStringFromCGRect(cell.frame));
    return cell;
}


- (CGSize)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout*)collectionViewLayout sizeForItemAtIndexPath:(NSIndexPath *)indexPath
{
    return CGSizeMake(60, 60);
}

- (UIEdgeInsets)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout*)collectionViewLayout insetForSectionAtIndex:(NSInteger)section
{
    UIEdgeInsets insets=UIEdgeInsetsMake(10, 10, 10, 10);
    return insets;
}

- (UICollectionReusableView *)collectionView:(UICollectionView *)collectionView viewForSupplementaryElementOfKind:(NSString *)kind atIndexPath:(NSIndexPath *)indexPath
{
    if ([kind isEqualToString:UICollectionElementKindSectionHeader]) {

        UICollectionReusableView *reusableview = [collectionView dequeueReusableSupplementaryViewOfKind:UICollectionElementKindSectionHeader withReuseIdentifier:@"HeaderView" forIndexPath:indexPath];

        if (reusableview==nil) {
            reusableview=[[UICollectionReusableView alloc] initWithFrame:CGRectMake(0, 0, 320, 44)];
        }

        UILabel *label=[[UILabel alloc] initWithFrame:CGRectMake(0, 0, 320, 44)];
        label.text=[NSString stringWithFormat:@"Recipe Group #%i", indexPath.section + 1];
        [reusableview addSubview:label];
        return reusableview;
    }
    return nil;
}