Logo Questions Linux Laravel Mysql Ubuntu Git Menu
 

Where to highlight UICollectionViewCell: delegate or cell?

According to the Collection View Programming Guide one should handle the visual state of the cell highlights in the UICollectionViewDelegate. Like this:

- (void)collectionView:(PSUICollectionView *)collectionView didHighlightItemAtIndexPath:(NSIndexPath *)indexPath {     MYCollectionViewCell *cell = (MYCollectionViewCell*)[collectionView cellForItemAtIndexPath:indexPath];     [cell highlight]; }  - (void)collectionView:(UICollectionView *)collectionView didUnhighlightItemAtIndexPath:(NSIndexPath *)indexPath {     MYCollectionViewCell *cell = (MYCollectionViewCell*)[collectionView cellForItemAtIndexPath:indexPath];     [cell unhighlight]; } 

What I don't like about this approach is that it adds logic to the delegate that is very specific to the cell. In fact, UICollectionViewCell manages its highlighted state independently, via the highlighted property.

Wouldn't overriding setHighlighted: be a cleaner solution, then?

- (void)setHighlighted:(BOOL)highlighted {     [super setHighlighted:highlighted];     if (highlighted) {         [self highlight];     } else {         [self unhighlight];     } } 

Are there any disadvantages to this approach instead of the delegate approach?

like image 321
hpique Avatar asked Mar 18 '13 17:03

hpique


People also ask

How do I highlight cells in collection view?

How to use? Just inherit BaseCollectionViewCell . If needed, configure in cell's init or collectionView 's delegate methods. If you don't need highlight effect, just find a method named 'shouldHighlightItemAtIndexPath' in UICollectionViewDelegate and return false or just set cell.

What is UICollectionViewDelegate?

The methods adopted by the object you use to manage user interactions with items in a collection view.


1 Answers

As the documentation says, you can rely on highlighted property to be changed while the cell is highlighted. For example the following code will make the cell red when highlighted (not its subviews though):

- (void)setHighlighted:(BOOL)highlighted {     [super setHighlighted:highlighted];     [self setNeedsDisplay]; }  - (void)drawRect:(CGRect)rect {     [super drawRect:rect];      if (self.highlighted) {         CGContextRef context = UIGraphicsGetCurrentContext();         CGContextSetRGBFillColor(context, 1, 0, 0, 1);         CGContextFillRect(context, self.bounds);     }  } 

And if you add something like this the background will become purple (red + opaque blue):

- (void)collectionView:(UICollectionView *)colView didHighlightItemAtIndexPath:(NSIndexPath *)indexPath {     UICollectionViewCell *cell = [colView cellForItemAtIndexPath:indexPath];     cell.contentView.backgroundColor = [UIColor colorWithRed:0 green:0 blue:1 alpha:0.5]; }  - (void)collectionView:(UICollectionView *)colView didUnhighlightItemAtIndexPath:(NSIndexPath *)indexPath {     UICollectionViewCell *cell = [colView cellForItemAtIndexPath:indexPath];     cell.contentView.backgroundColor = nil; } 

So you can use both together (not necessarily both changing the cell appearance). The difference is that with delegate methods you also have indexPath. It might be used to create multi-selection (you will use this methods together with selection delegate methods), to show some preview while the cell is highlighted, to show some animation with other views... There's quite a few appliance for this delegate methods in my opinion.

As a conclusion, I would leave the cell appearance to be handled by the cell itself and use delegate methods to let controller make something cool in the same time.

like image 125
A-Live Avatar answered Sep 24 '22 00:09

A-Live