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1) Añadir UICollectionViewDataSource, UICollectionViewDelegateFlowLayout

2) en ViewDidLoad:
         self.collectionView.delegate = self;
         self.collectionView.dataSource = self;
        
                self.collectionView.register(UINib(nibName: "ShowCell", bundle: nil), forCellWithReuseIdentifier: "ShowCell")
        
3)

    //MARK: CollectionView
     
     func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
        return self.categories.count;
     
     }
     
     func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
     
        let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "MainPictoCell", for: indexPath) as! MainPictoCell
        
        let tag = self.categories[indexPath.row];
        
        if(tag.picture != nil){
            let link = URL(string:(tag.picture!.path!));
            if (link?.absoluteString.hasPrefix("http"))! {
                cell.imgPicto.sd_setImage(with: link, placeholderImage: #imageLiteral(resourceName: "placeholder"));
            } else {
                do {
                    let path = ApplicationModel.sharedInstance.picturesDirectoryPath.appendingPathComponent((link?.absoluteString)!);
                    let imageData = try Data(contentsOf: path)
                    cell.imgPicto.image = UIImage(data: imageData);
                } catch {
                    print("Error loading image : \(error)")
                }
            }
        }
        else{
            cell.imgPicto.image = #imageLiteral(resourceName: "placeholder");
        }
        
        if (tag.crossed) {
            cell.imgCross.isHidden = false;
        } else {
            cell.imgCross.isHidden = true;
        }
        
        let (name, translated) = tag.getName();
        cell.lblName.text = name.uppercased();
        if(translated){
            cell.lblName.textColor = UIColor.white;
        }
        else{
            cell.lblName.textColor = UIColor.red;
        }
        
        cell.tag = indexPath.row;
        let tagTap: UITapGestureRecognizer = UITapGestureRecognizer(target: self, action: #selector(goTags(sender:)))
         cell.isUserInteractionEnabled = true;
         cell.addGestureRecognizer(tagTap)
        
        return cell;
     }
     
     func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) {
        //selectedCategory = self.categories[indexPath.row];
        
       // self.performSegue(withIdentifier: "showTagDetail", sender: self);
     }
    
    func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeForItemAt indexPath: IndexPath) -> CGSize {
        
        let dim = MainController.calculateImageSize(width:collectionView.bounds.width);
        return CGSize(width: dim, height: dim + CGFloat(AppConstants.Viewer.LABEL_SIZE))
    }
    
    func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, minimumLineSpacingForSectionAt section: Int) -> CGFloat {
        return CGFloat(2.0);
    }
    
    func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, minimumInteritemSpacingForSectionAt section: Int) -> CGFloat {
        return CGFloat(2.0);
    }
    
    func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, insetForSectionAt section: Int) -> UIEdgeInsets {
        return UIEdgeInsetsMake(0.0, AppConstants.Viewer.SPACE_BETWEEN_CELLS, 0.0, AppConstants.Viewer.SPACE_BETWEEN_CELLS);
    }

0) La view que se incrustará, se pone como view dentro de un XIB collectionViewCell

1) en el .h de la clase indicar el delegate y datasource
@interface RTShowsController : RTViewController <UICollectionViewDelegate, UICollectionViewDataSource>

2) en viewDidLoad asignar:
- (void)viewDidLoad {
    [super viewDidLoad];
    // Do any additional setup after loading the view.
    //Asignamos DataSource y Delegate
    self.collectionView.delegate = self;
    self.collectionView.dataSource = self;
    
    //Asociamos el XIB que incrustaremos
    [self.collectionView registerClass:RTShowCell.class forCellWithReuseIdentifier:@"RTShowCell"];
    [self.collectionView registerNib:[UINib nibWithNibName:@"RTShowCell" bundle:nil] forCellWithReuseIdentifier:@"RTShowCell"];
}


3) Implementar métodos de sección
-(NSInteger)numberOfSectionsInCollectionView:(UICollectionView *)collectionView {
    return 1;
}

-(NSInteger)collectionView:(UICollectionView *)collectionView numberOfItemsInSection:(NSInteger)section {

    return [self.showsList count];
}

-(UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath {

    static NSString *cellIdentifier = @"RTShowCell";
    
    RTShowCell *cell = [collectionView dequeueReusableCellWithReuseIdentifier:cellIdentifier forIndexPath:indexPath];

    
    RTShow* show = [self.showsList objectAtIndex:indexPath.row];
   
    NSURL* imagePath = [NSURL URLWithString:show.showThumbnail];
    
    dispatch_async(dispatch_get_main_queue(), ^{
        [cell.vwContent.imgShow loadImageFromURL:[imagePath absoluteString] andPlaceholder:[UIImage imageNamed:DEFAULT_IMAGE]];
    });
    
    cell.vwContent.lblSchedule.text = show.showTime;
  
    return cell;
    
}

- (CGSize)collectionView:(UICollectionView *)collectionView
                  layout:(UICollectionViewLayout *)collectionViewLayout
  sizeForItemAtIndexPath:(NSIndexPath *)indexPath
{
    
    NSLog(@"%f",self.view.frame.size.width);

    
    return CGSizeMake((self.view.frame.size.width / 2) -1, (self.view.frame.size.width / 2));
}


#pragma mark collection view cell paddings
- (UIEdgeInsets)collectionView:(UICollectionView*)collectionView layout:(UICollectionViewLayout *)collectionViewLayout insetForSectionAtIndex:(NSInteger)section {
    return UIEdgeInsetsMake(0, 0, 0, 0); // top, left, bottom, right
}

- (CGFloat)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout*)collectionViewLayout minimumInteritemSpacingForSectionAtIndex:(NSInteger)section {
    
    return 0;
}

- (CGFloat)collectionView:(UICollectionView*)collectionView layout:(UICollectionViewLayout *)collectionViewLayout minimumLineSpacingForSectionAtIndex:(NSInteger)section {
    return 2; 
}

-(void)collectionView:(UICollectionView *)collectionView didSelectItemAtIndexPath:(NSIndexPath *)indexPath{
    
    selectedProgram = (int) indexPath.row;
    
    [self performSegueWithIdentifier:@"showProgram" sender:self];
    
}