How make a collectionViewCell auto size only by he

问题:

I use feature of autosizing flow layout of collectionView

self.flow = [[UICollectionViewFlowLayout alloc] init];
self.flow.scrollDirection = UICollectionViewScrollDirectionVertical;
self.flow.sectionInset = UIEdgeInsetsZero;
self.flow.estimatedItemSize = CGSizeMake(320, 48);

I want to cells will fill by width full width of CollectionView (widthCell=widthCollectionView)

But i got what autosizing work for whole size. I try playing with Content Compression/Hugging Priority - not effect.

With width of CollectionView equals 320px, i got cell size for label content size.

My cell looks like

Constraints Horizontal : H:|-8-[img(48)]-8-[label]-8-|

How to make autosize work only for Vertical but not for Horizontal?

回答1:

I found a solution.

CollectionViewCell has a delegate preferredLayoutAttributesFittingAttributes

So, this function gives you layoutAttributes sets as estimatedItemSize

You need do next (for Height)

- (UICollectionViewLayoutAttributes *)preferredLayoutAttributesFittingAttributes:(UICollectionViewLayoutAttributes *)layoutAttributes {
    UICollectionViewLayoutAttributes *attr = [super preferredLayoutAttributesFittingAttributes:layoutAttributes]; //Must be called
    CGRect frame = attr.frame;
    frame.size.width = layoutAttributes.size.width; //Key here
    attr.frame = frame;
    return attr;
}

Same you can do to prefer size, width so make constant height (frame.size.height = layoutAttributes.size.height).

If you just copy layoutAttributes and change width, will no effect!

You must call super.

回答2:

Actually you are right here is the problem with the constraints priority.

To resolve the priority constraint issue you should update the imageView Leading priority 999 and also label Trailing priority 999 either programmatically or directly from InterFace Builder.

Update priority programmatically by using the KVConstraintExtensionsMaster that I have implemented to update any constraint without IBOutlet reference of Autolayout constraint.

-(UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath
{
    CustomCell *cell = [collectionView dequeueReusableCellWithReuseIdentifier:@"Cell1" forIndexPath:indexPath];

    [cell.imageView changeAppliedConstraintPriority:999 forAttribute:NSLayoutAttributeLeading];
    [cell.label changeAppliedConstraintPriority:999 forAttribute:NSLayoutAttributeTrailing];

    return cell;
}

After this Now you need to calculate the only height of the cell

- (CGSize)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewLayout*)collectionViewLayout sizeForItemAtIndexPath:(NSIndexPath *)indexPath {
     CGFloat width  = CGRectGetWidth(collectionView.bounds);
     CGFloat height  =  /* do here some calculation for height */
     return CGSizeMake(width, height);;
}

回答3:

Dmitry Nelepov's solution in swift.

Swift 4

override func preferredLayoutAttributesFitting(_ layoutAttributes: UICollectionViewLayoutAttributes) -> UICollectionViewLayoutAttributes {
    let attr = super.preferredLayoutAttributesFitting(layoutAttributes)
    var frame = attr.frame
    frame.size.width = layoutAttributes.size.width //Key here
    attr.frame = frame
    return attr
}