IOS UICollectionView Cell with different instance of cell class

Question

I am trying to create custom cell for UiCollectionView where I need to update each cell from background.

So I have created custom class for each cell named Cell_Obj and updating the cell content from the Cell_Obj itself using a timer.

The below code add an image on cell and increment a counter in each 2 second and display it on new cell label.

On each time when I add new cell using a button on a viewcotroller the cell updating but every cell getting the same value on the label. It suppose to have different counter value as each cell is different instance of Cell_Obj but the counter value and labelTxt (the cell number) has the same value when each time the timer triggered.

ViewController.h

#import <UIKit/UIKit.h>
#import "Cell_Obj.h"

@interface ViewController : UIViewController<UICollectionViewDataSource,UICollectionViewDelegate>

@property (weak, nonatomic) IBOutlet UICollectionView *collection;

@end

ViewController.m

#import "ViewController.h"

@interface ViewController (){

    NSMutableArray *GridArray;
}

@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    [self.collection setDelegate:self];
    [self.collection setDataSource:self];
    // Do any additional setup after loading the view, typically from a nib.

        GridArray = [[NSMutableArray alloc] init];
}

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


- (NSInteger)collectionView:(UICollectionView *)collectionView numberOfItemsInSection:(NSInteger)section{
    return GridArray.count;
}

// The cell that is returned must be retrieved from a call to -dequeueReusableCellWithReuseIdentifier:forIndexPath:
- (Cell_Obj *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath{
    Cell_Obj *cell = [collectionView dequeueReusableCellWithReuseIdentifier:@"Cell" forIndexPath:indexPath];
   // cell.label.text = @"123";

    /*cell.imageView.image = [UIImage imageNamed:[NSString stringWithFormat:@"AppIcon.png",indexPath.row]];*/
    return cell;

}

- (void)addImage
{
     Cell_Obj *cell = [[Cell_Obj alloc] init];

   // cell.label.text = @"123";

    //cell.label.text =  [NSString stringWithFormat:@"%d",[dvrGridArray count]-1];
    NSString * txt = [NSString stringWithFormat:@"%d",[GridArray count]];
    [cell updateTextLabelName: txt];


    [GridArray addObject:cell];
    [_collection insertItemsAtIndexPaths:@[[NSIndexPath indexPathForItem:[GridArray count]-1 inSection:0]]];


      /*  NSMutableArray *arrayWithIndexPaths = [NSMutableArray array];
        [arrayWithIndexPaths addObject:cell];

        [self.collection insertItemsAtIndexPaths:arrayWithIndexPaths];*/

}


- (IBAction)addClicked:(id)sender {

    [self addImage];

}
- (IBAction)changeImage:(id)sender {

   // DVR_Obj *cell = [dvrGridArray objectAtIndex:0];
   // [cell changeImage ];
   // [_collection reloadData];
     NSIndexPath *indexPath = [NSIndexPath indexPathForRow:1 inSection:0];
    Cell_Obj *cell =  [_collection cellForItemAtIndexPath:indexPath];
   [cell changeImage ];

}

#pragma mark Collection view layout things
// Layout: Set cell size
- (CGSize)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout*)collectionViewLayout sizeForItemAtIndexPath:(NSIndexPath *)indexPath {

    //NSLog(@"SETTING SIZE FOR ITEM AT INDEX %d", indexPath.row);

    CGRect screenRect = [[UIScreen mainScreen] bounds];
    CGFloat screenWidth = screenRect.size.width;
    CGFloat screenHeight = screenRect.size.height;

    CGSize mElementSize = CGSizeMake((screenWidth/4)-2, (screenHeight/4)-2);
    return mElementSize;
}
- (CGFloat)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout*)collectionViewLayout minimumInteritemSpacingForSectionAtIndex:(NSInteger)section {
    return 1.0;
}

- (CGFloat)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout*)collectionViewLayout minimumLineSpacingForSectionAtIndex:(NSInteger)section {
    return 1.0;
}

// Layout: Set Edges
- (UIEdgeInsets)collectionView:
(UICollectionView *)collectionView layout:(UICollectionViewLayout*)collectionViewLayout insetForSectionAtIndex:(NSInteger)section {
    // return UIEdgeInsetsMake(0,8,0,8);  // top, left, bottom, right
    return UIEdgeInsetsMake(1,1,1,1);  // top, left, bottom, right
}

@end

Cell_Obj.h

#import <UIKit/UIKit.h>

@interface Cell_Obj : UICollectionViewCell
@property (weak, nonatomic) IBOutlet UIImageView *imageView;
@property (weak, nonatomic) IBOutlet UILabel *label;


- (void)changeImage;
- (void)updateTextLabelName:(NSString*)str;
@end

Cell_Obj.m

#import "Cell_Obj.h"

static NSString *labelTxt ;// = [[NSString alloc] init];
static int  counter;

@implementation Cell_Obj{



}

+ (void)initialize {
    if (self == [Cell_Obj class]) {
        labelTxt = [[NSString alloc] init];
        counter=0;

    }
}


- (id)initWithFrame:(CGRect)frame
{

    self = [super initWithFrame:frame];
    if (self) {


    }
    return self;
}


- (void)awakeFromNib {

    _imageView.image = [UIImage imageNamed:@"flower1.png"];

    _label.text = labelTxt;

    [NSTimer scheduledTimerWithTimeInterval:2.0f
                                     target:self
                                   selector:@selector(updateImage)
                                   userInfo:nil
                                    repeats:YES];
}


- (void)updateImage
{
    _imageView.image = [UIImage imageNamed:@"AppIcon.png"];

    counter++;
    NSString * txt = [NSString stringWithFormat:@"%@-%d",labelTxt,counter];
     _label.text = txt;
}

- (void)updateTextLabelName :(NSString*)str
{

    labelTxt = str;
}



@end

Answer 1

Your each cell is not new cell. Cell_Obj *cell = [collectionView dequeueReusableCellWithReuseIdentifier:@"Cell" forIndexPath:indexPath]; this statement reuses your cell with identifier "Cell". To create new cell each time , don't pass indexPath , pass nil instead.