If we want to fadeIn the selected cell of collection view then use the following code-

Sometimes we need to show the selected cell . For example - If we have list of songs and we want to display which song is currrently playing then FadeIn method can be useful.

In this code first we need to get the indexpath of selected cell and then we can get the cell from indexpath.

After that we initialize cagradientlayer and set frame and color of gradientlayer then we mask that layer on the content view of cell.

Use this method in -didSelectItemAtIndexPath.

Here is the code-

-(void)setfadeInCell{
    
// here selectedIndex is the index path of selected cell.
    NSIndexPath *iPath = [NSIndexPath indexPathForItem:self.selectedIndex inSection:0];

//get the cell from index path
    UICollectionViewCell *cell1=(UICollectionViewCell *)[self.collectionViewVideo cellForItemAtIndexPath:iPath];

//scroll the collection view to the selected row
    [self.collectionViewVideo scrollToItemAtIndexPath:iPath atScrollPosition:UICollectionViewScrollPositionCenteredHorizontally animated:NO];

// initialize the gradient layer
    CAGradientLayer *gradient = [CAGradientLayer layer];
//set frame of gradient layer
    gradient.frame = cell1.contentView.bounds;
//chnage the color of mask here
    gradient.colors = @[(id)[UIColor clearColor].CGColor, (id)[UIColor blackColor].CGColor];
    gradient.locations = @[@0.0, @(1.5)];
    cell1.layer.mask = gradient;

//optional-assign tag to the cell and set interaction
    [cell1 setTag:9999];
    [cell1 setUserInteractionEnabled:NO];


}

Now if you want to remove this after selecting the new cell then use the following code in -didSelectItemAtIndexPath -

    [collectionView viewWithTag:9999].layer.mask=nil;
    [[collectionView viewWithTag:9999]setUserInteractionEnabled:YES];
    [[collectionView viewWithTag:9999] setTag:0];