现在有这么一个场景，我tabelViewCell里面嵌套了uicollectionView，但是uicollectionView的高度是不确定的，我利用自动布局计算UITabelViewCell的高度，UITabelViewCell内部高度由UICcollectionView撑开。但是发现每次刚进来的时候计算有误差，后来发现collectionViewContentSize这哥size是不准确的。宽度比我计算的小，所以高度计算不准。解决方法：
self.collectionView.collectionViewLayout.invalidateLayout()
self.collectionView.reloadData()
self.collectionView.setNeedsLayout()
self.collectionView.layoutIfNeeded()
let h = self.collectionView.collectionViewLayout.collectionViewContentSize.height
self.h = h
self.collectionView.snp.updateConstraints { make in
make.height.equalTo(h)
}
或者
override func systemLayoutSizeFitting(_ targetSize: CGSize, withHorizontalFittingPriority horizontalFittingPriority: UILayoutPriority, verticalFittingPriority: UILayoutPriority) -> CGSize {
let size = super.systemLayoutSizeFitting(targetSize, withHorizontalFittingPriority: horizontalFittingPriority, verticalFittingPriority: verticalFittingPriority)
self.collectionView.layoutIfNeeded()
let height = self.collectionView.collectionViewLayout.collectionViewContentSize.height
return CGSize(width: size.width,height: size.height + height)
}
