问题

I have a added a UICollectionView to my UIViewController and have made a custom cell for it.

I set the size of the cell using the sizeForItemAtIndexPath method and set each cell to be UIScreen.mainScreen().bounds.width/2 in both height and width. So essentially, each cell is half the screen wide and this same length in height.

I then have an UIImageView inside the cell with each edge pinned to its relative edge of the cell so that the image view fills the cell. I also have a UILabel that is centred both vertically and horizontally in the cell.

However on first load, the cell is the correct size but the content is much smaller in a tiny square in the top left. (Seen in the image below, I have set the cell's contentView background color to green and the imageView background color to red).

Then after scrolling down a little bit (and I assume a reusable cell being dequeued) all of the cells are fine (and remain fine after scrolling back up).

What is causing the content to not be constrained properly on first load?

UPDATE

Some of the code from my UIViewController:

func collectionView(collectionView: UICollectionView, cellForItemAtIndexPath indexPath: NSIndexPath) -> UICollectionViewCell {
        var cell = collectionView.dequeueReusableCellWithReuseIdentifier("PrevDrawCell", forIndexPath: indexPath) as? PrevDrawCell

        if cell == nil {
            cell = PrevDrawCell()
        }

        cell!.drawVC = self
        cell!.imageShortCode = self.tempImageURLs[indexPath.row]

        // Pull image (async) and set after download
        cell!.setupImage()

        cell!.contentView.backgroundColor = UIColor.greenColor()
        cell!.coverView.backgroundColor = UIColor.redColor()

        cell!.dateLabel.font = UIFont(name: "HelveticaNeue-Light", size: 26)
        cell!.dateLabel.text = "\(self.tempImageURLs.count-indexPath.row)/9"

        return cell!
}

func collectionView(collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeForItemAtIndexPath indexPath: NSIndexPath) -> CGSize {
    let size = UIScreen.mainScreen().bounds.width/2
        return CGSize(width: size, height: size)
}


func collectionView(collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, insetForSectionAtIndex section: Int) -> UIEdgeInsets {
        return UIEdgeInsetsZero
}

func collectionView(collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, minimumInteritemSpacingForSectionAtIndex section: Int) -> CGFloat {
    return 0
}

func collectionView(collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, minimumLineSpacingForSectionAtIndex section: Int) -> CGFloat {
    return 0
}

回答1:

It looks like it still retains it's 100x100px basic size for the contentView while the cell itself gets the right size already. You can force the layout to reset adding the following line just before you return the cell:

cell?.layoutIfNeeded()

回答2:

I had once similar problem (content of my cell was not fitting cell even with correct autolayout). The bug was caused by not calling super.layoutSubviews() in overriden function layoutSubviews() that was in Cell's class.

回答3:

For those using Storyboard + AutoLayout, and choosing which constraints are active at runtime:

When using dequeueReusableCell, on first load, the cell is created but its view has not been initialised, so the constraint changes aren't saved - whatever you have set in Storyboard is used. Solution for me was to update the constraints after the view has loaded:

override func layoutSubviews() {
    super.layoutSubviews()
    adjustIconWidths()
}

回答4:

Thanks to the great tip by vin047.

In our case I found that the super-call-order issue was the problem.

But with the overall table view (or collection view). Not in the cell as such.

Works:

class UnusualCollectionView: UICollectionView {
    override func layoutSubviews() {
        super.layoutSubviews()
        contentInset = UIEdgeInsets(top: 10, left: 0, bottom: 10, right: 0)
    }

Fails very erratically, particularly on first appearance:

class UnusualCollectionView: UICollectionView {
    override func layoutSubviews() {
        contentInset = UIEdgeInsets(top: 10, left: 0, bottom: 10, right: 0)
        super.layoutSubviews()
    }

The problem caused some profoundly erratic behavior. For example, the 12th cell (no really) was always displaced a long way vertically. Always the 12th cell! Who knows?

vin047 saved the day here, bravo.

来源：https://stackoverflow.com/questions/32593117/uicollectionviewcell-content-wrong-size-on-first-load

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ios