Change attributes of a UICollectionViewCell in didSelectItemAtIndexPath - ios

Question

I am configuring a UICollectionViewCell in a subclass, it adds 2 subviews to the contentView property, both are UIImageView and both have the hidden property set to YES. These subviews are "checked" and "unchecked" images that overlay the primary UIImageView in the cell to indicate whether or not the current cell is selected using UICollectionView's "multiple select" feature.
When the cell is tapped, collectionView:didSelectItemAtIndexPath: is called on the delegate, and I'd like to setHidden:NO on the "checked" UIImageView. Calling this on the cell does nothing at all -- the cell is seemingly locked in its originally drawn state.
Is it possible to make changes to a cell outside collectionView:cellForItemAtIndexPath:? I have tried manually adding subviews within collectionView:didSelectItemAtIndexPath:, but it just makes absolutely no change to the UI. I have verified that the delegate method is getting called, it's just not making my cell changes.
- (void) collectionView(UICollectionView *)cv didSelectItemAtIndexPath(NSIndexPath *)indexPath {
ShotCell *cell = [self collectionView:cv cellForItemAtIndexPath:indexPath];
UILabel *testLabel = UILabel.alloc.init;
testLabel.text = #"FooBar";
testLabel.sizeToFit;
[cell.contentView.addSubview testLabel];
}

Answer 1

The way you're trying to do this is incorrect. You need to keep a reference to the selected cell or cells in a property. In this example, I use an array to hold index paths of the selected cells, then check whether the index path passed in to cellForItemAtIndexPath is contained in that array. I unselect the cell if you click on one that's already selected:
#interface ViewController ()
#property (strong,nonatomic) NSArray *theData;
#property (strong,nonatomic) NSMutableArray *paths;
#end
#implementation ViewController
- (void)viewDidLoad {
[super viewDidLoad];
self.paths = [NSMutableArray new];
self.theData = #[#"One",#"Two",#"Three",#"Four",#"Five",#"Six",#"Seven",#"Eight"];
[self.collectionView registerNib:[UINib nibWithNibName:#"CVCell" bundle:nil] forCellWithReuseIdentifier:#"cvCell"];
UICollectionViewFlowLayout *flowLayout = [[UICollectionViewFlowLayout alloc] init];
[flowLayout setScrollDirection:UICollectionViewScrollDirectionVertical];
[self.collectionView setCollectionViewLayout:flowLayout];
}
-(NSInteger)collectionView:(UICollectionView *)collectionView numberOfItemsInSection:(NSInteger)section {
return self.theData.count;
}
-(CVCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath {
static NSString *cellIdentifier = #"cvCell";
CVCell *cell = (CVCell *) [collectionView dequeueReusableCellWithReuseIdentifier:cellIdentifier forIndexPath:indexPath];
cell.backgroundColor = [UIColor whiteColor];
cell.label.text = self.theData[indexPath.row];
if ([self.paths containsObject:indexPath]) {
[cell.iv setHidden:NO]; // iv is an IBOutlet to an image view in the custom cell
}else{
[cell.iv setHidden:YES];
}
return cell;
}
-(void)collectionView:(UICollectionView *)collectionView didSelectItemAtIndexPath:(NSIndexPath *)indexPath {
if ([self.paths containsObject:indexPath]) {
[self.paths removeObject:indexPath];
}else{
[self.paths addObject:indexPath];
}
[self.collectionView reloadItemsAtIndexPaths:#[indexPath]];
}
- (CGSize)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout*)collectionViewLayout sizeForItemAtIndexPath:(NSIndexPath *)indexPath {
return CGSizeMake(150, 150);
}