UICollectionView cell subviews do not resize

问题:

In a CollectionView, some cells should have an additional subview or layer. The CollectionView can be told to resize it's cells, thus all content needs to resize appropriately.

Currently, the cell is initialized from a nib containing a cell with imageview; the cell nib is linked to a custom UICollectionViewCell subclass, that only does the init. Autoresize subviews is checked.

The CollectionView is told to resize the cell by a value derived and returned in sizeForItemAtIndexPath:. I have subclassed a FlowLayout but it only specifies ScrollDirection and Insets.

All of that is working fine. Problem: How do I add subview/layer to the cell so it also resizes correctly? I tried adding subviews and layers with translatesAutoresizingMaskIntoConstraints off, but these do not automatically change size at all. Also tried to use code frame/view instead of nib.

The best I got now is a cell.contentView.layer sublayer which I add in cellForItemAtIndexPath:; that is "manually" resized by storing the cell's frame.size from sizeForItemAtIndexPath:, which is not only ugly but also ends up with the sublayer having various sizes for different cells.

Any help appreciated!

回答1:

I ran into the same issue just now.

When using the UICollectionViewFlowLayoutDelegate method to set the cell size depending on device and device-orientation, the size would be calculated properly but subviews would not resize to fill the newly size cell. The effect was a large blank cell with small subviews that don't fill the cell's bounds / remain the size equal to their current value in the xib file.

I solved this by doing the following in awakeFromNib:

- (void)awakeFromNib
{
    [super awakeFromNib];

    self.contentView.autoresizingMask = UIViewAutoresizingFlexibleHeight | UIViewAutoresizingFlexibleWidth;
    self.contentView.translatesAutoresizingMaskIntoConstraints = YES;
}

Prior to doing this, the contentView mask was nil.

回答2:

*override func awakeFromNib() {
    super.awakeFromNib()

    self.contentView.autoresizingMask.insert(.FlexibleHeight)
    self.contentView.autoresizingMask.insert(.FlexibleWidth)
}

This worked for me.. This code goes inside of your subclassed UICollectionViewCell.swift file (where your code involving the custom cell is located)

Swift solution*

回答3:

As an alternative to enabling AutoResizingMask, for custom UICollectionViewLayouts that have variable height for example where you are setting some constraints manually and need translatesAutoresizingMaskIntoConstraints to remain NO, you can add the following to layoutSubviews in the cell:

self.contentView.frame = self.bounds;

This worked to fix all of my custom collection view layouts that had problens with Xcode 6.

回答4:

In another project without xibs i subclassed UICollectionViewCell and did this for the same effect:

#import "CVcell.h"

@implementation CVcell

@synthesize cellImage;

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

        CGFloat cellSize = self.contentView.bounds.size.width;
        cellImage = [[UIImageView alloc]initWithFrame:CGRectMake(0, 0, cellSize, cellSize)];
        [cellImage setClipsToBounds:YES];

        cellImage.translatesAutoresizingMaskIntoConstraints = NO;
        cellImage.autoresizingMask = UIViewAutoresizingFlexibleHeight | UIViewAutoresizingFlexibleWidth;
        [self.contentView addSubview:cellImage];

    }
    return self;
}

@end

回答5:

I always prefer autolayout when possible. But Sometimes usings frames and bounds just is a timesaver when a view is determined straightforward by only its superview.

In the case of UICollectionViewCell I set an image to be the cells frame + self.imageView.autoresizingMask = UIViewAutoresizingFlexibleWidth | UIViewAutoresizingFlexibleHeight;

But when I had different sizes of cells in the collectionView it messed up things and the image sometimes took the size of a different cell.

So I turned to working with the the cells bounds and - ye that acually worked out fine.

So maybe give that a try?

回答6:

A simple auto layout solution is to set constraints to the container view.

So if we have an image view with a parent view, we basically want to tell the subview (the image view) to maintain a leading, trailing, bottom, and top space distance of 0 to the container view.

回答7:

@Alfie Hanssen solution (here) didn't work properly for me, according with this article:

The size of the cell view in the XIB is 50 x 50 points, which is the default size of the collection view cells as set in the flow layout. Even if it’s a bit hard to work with a cell this small in Interface Builder, it’s better to not change the default size. The problem is that Auto Layout considers the manually set size as being fixed and generates a NSAutoresizingMaskLayoutConstraint error when it tries to adjust the cells height automatically

I have inspected the UICollectionViewCell and I found that there is a view between the cell and the contentView, and that view has intrinsic width and height constraints. Instead of the AutoresizingMask I'm just updating as below and seems working for me.

override func layoutSubviews() {
    contentView.superview?.frame = bounds
    super.layoutSubviews()
}

回答8:

The solution was to turn off AutoConstraints for the cell xib and activate the flexible width/height arrows in the AutoResize for the imageviews.

回答9:

I'm adding subView and constraint programmatically, the following code works for me:

lazy var imageView: UIImageView = { [unowned self] in
    let imageView = UIImageView(frame: self.contentView.frame)
    imageView.contentMode = .scaleAspectFill
    imageView.clipsToBounds = true

    return imageView
}() 

func updateCellWith(image: UIImage) {

    contentView.subviews.forEach { $0.removeFromSuperview() }

    contentView.addSubview(imageView)
    imageView.topAnchor.constraint(equalTo: contentView.topAnchor, constant: 0).isActive = true
    imageView.leftAnchor.constraint(equalTo: contentView.leftAnchor, constant: 0).isActive = true
    imageView.rightAnchor.constraint(equalTo: contentView.rightAnchor, constant: 0).isActive = true
    imageView.bottomAnchor.constraint(equalTo: contentView.bottomAnchor, constant: 0).isActive = true

    self.imageView.autoresizingMask.insert(.flexibleHeight)
    self.imageView.autoresizingMask.insert(.flexibleWidth)

    imageView.image = image

}

回答10:

I had the same problem. Switching between two layouts did not resize the Pictures (UIImage) inside my cells. My Cells where build without a xib. And I used two different cell classes for each CollectionViewCustomLayout.

I fixed this programatically with this:

self.autoresizesSubviews = YES;

in my UICollectionViewCell subclasses.

But this only worked for me by adding the Picture as a cells backgroundpicture like this:

cell.backgroundView[[UIImageView alloc] initWithImage: SumDummyImage ];