UICollectionViewController with Flow Layout Crash

Question

I've just created a UICollectionViewController programatically. Up to here everything is fine but I'm facing some problems. My app immediately crashes when the CollectionViewController is called, returning this error.

'UICollectionView must be initialized with a non-nil layout parameter'

I tried to insert UICollectionViewFlowLayout of course, but it continues to crash and I do not understand why. Can someone explain to me how to use a UICollectionViewController without using the storyboard ??

Where am I doing wrong?

@implementation ChooseRegion

static NSString * const reuseIdentifier = @"Cell";

- (void)viewDidLoad {
    [super viewDidLoad];

    // Uncomment the following line to preserve selection between presentations
    // self.clearsSelectionOnViewWillAppear = NO;

    // Register cell classes
    [self.collectionView registerClass:[UICollectionViewCell class] forCellWithReuseIdentifier:reuseIdentifier];

    UICollectionViewFlowLayout *layout = [[UICollectionViewFlowLayout alloc] init];
    layout.minimumLineSpacing = 0;
    layout.minimumInteritemSpacing = 0;
    layout.itemSize = CGSizeMake(100, 100);

    self.collectionView = [[UICollectionView alloc] initWithFrame:self.view.frame collectionViewLayout:layout];

    // Do any additional setup after loading the view.
}


- (void)didReceiveMemoryWarning {
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}

/*
#pragma mark - Navigation

// In a storyboard-based application, you will often want to do a little preparation before navigation
- (void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender {
    // Get the new view controller using [segue destinationViewController].
    // Pass the selected object to the new view controller.
}
*/

#pragma mark <UICollectionViewDataSource>

- (NSInteger)numberOfSectionsInCollectionView:(UICollectionView *)collectionView {
#warning Incomplete implementation, return the number of sections
    return 0;
}


- (NSInteger)collectionView:(UICollectionView *)collectionView numberOfItemsInSection:(NSInteger)section {
#warning Incomplete implementation, return the number of items
    return 0;
}

- (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath {
    UICollectionViewCell *cell = [collectionView dequeueReusableCellWithReuseIdentifier:reuseIdentifier forIndexPath:indexPath];

    // Configure the cell

    return cell;
}

@ReinierMelian you can't just call a method over an object without initializing it. Sh_Khan's answer is the only correct way. — Alejandro Iván, Feb 22 '18 at 17:55
Does your `UICollectionView` come from a Storyboard? Or are you creating it programmatically? — Alejandro Iván, Feb 22 '18 at 17:56
@ReinierMelian you're not. You are just allocating memory, but you never call `init` or `initWithFrame:collectionViewLayout:`. — Alejandro Iván, Feb 22 '18 at 17:57
Can you please post the method where you are creating the `UICollectionView`? — Alejandro Iván, Feb 22 '18 at 17:59
@AlejandroIván I'm edit my question with all code of my collectionViewController.m — kAiN, Feb 22 '18 at 18:01
So your view controller is actually a subclass of `UICollectionViewController`? Make it a subclass of `UIViewController`, since `UICollectionViewController` already has a `UICollectionView` automatically embedded. — Alejandro Iván, Feb 22 '18 at 18:02
@AlejandroIván. if I render uicollectionViewcontroller a UIViewController I should create a new collectionView object and insert it in the viewcontroller .. I want to use collectionViewController because I already needed all the movement of its scrollView — kAiN, Feb 22 '18 at 18:07
inside collectionViewController don't create a collectionView actually it's designated with it set it parameteres only all we talked about expecting you create it inside a UIViewController subclass — Shehata Gamal, Feb 22 '18 at 18:09
I may not be able to use a collectionViewController anymore.. its incredible — kAiN, Feb 22 '18 at 18:10
see here https://www.appcoda.com/ios-programming-uicollectionview-tutorial/ — Shehata Gamal, Feb 22 '18 at 18:14
@Sh_Khan this link use storyboard... I not need of storyboard... the implementation of uicollectionViewController programmatically is equal to link — kAiN, Feb 22 '18 at 18:16

score 1 · Answer 1 · answered Feb 22 '18 at 18:27

If you're using (or have subclassed) a UICollectionViewController, it already has a UICollectionView instance assigned. You don't need to instantiate or create a new one. I suspect the reason this isn't working is because you aren't adding the new view to the hierarchy (even though you're assigning it to self.collectionView.

Instead of self.collectionView = [[UICollectionView alloc] init...

Just assign the layout to your existing UICollectionView, eg:

self.collectionView.collectionViewLayout = layout

kAiN · Accepted Answer · 2018-02-22T18:48:57.190

Solved my problem ... Thank you all for the many tips and suggestions you gave me in this .. you were very kind !!

all this problem occurs because the UICollectionViewController is not initialized with its layout at the time of its presentation.

I call UICollectionViewController from another UIViewController using the [self presentViewController:collectionViewController animated:YES completion:nil] method .... At this point the problem occurs ...

The UICollectionViewController was only allocated to be presented and did not have the necessary layout to be shown ... that's why this damn crash !!!

So I solved this way

UIViewController.m

-(void)presentCollectionViewController {
    UICollectionViewFlowLayout * layout = [[UICollectionViewFlowLayout alloc] init];
    layout.minimumLineSpacing = 0;
    layout.minimumInteritemSpacing = 0;
    layout.itemSize = CGSizeMake (100, 100);
    [layout setScrollDirection: UICollectionViewScrollDirectionHorizontal];
    
    UICollectionViewController * chooseRegion = [[UICollectionViewController alloc] initWithCollectionViewLayout:layout];

    [self presentViewController: chooseRegion animated: YES completion: nil];
}

UICollectionViewController.m

-(void)viewDidLoad {
    [super viewDidLoad];

    // Register cell classes
    [self.collectionView registerClass:[UICollectionViewCell class] forCellWithReuseIdentifier:reuseIdentifier];

}

At this point everything works ...

Inside the UICollectionViewController you do not need to specify any type of layout in this case, as it is specified during the allocation of the class before its presentation

UICollectionViewController with Flow Layout Crash

2 Answers2