iOS 解决UICollectionView 计算 Cell 大小的问题

 let ITEM_MIN_WIDTH: CGFloat = 300
  let ITEM_SPACING: CGFloat = 6

  func resizeCollectionView(size: CGSize) {
    if let layout = collectionView?.collectionViewLayout as? UICollectionViewFlowLayout {
      layout.minimumLineSpacing = ITEM_SPACING
      layout.minimumInteritemSpacing = ITEM_SPACING

      var itemCount = Int(size.width / ITEM_MIN_WIDTH)
      if itemCount == 0 {
        itemCount = 1
      }

      if itemCount == 1 {
        layout.itemSize = CGSizeMake(size.width, size.width * 10 / 16)
        layout.sectionInset = UIEdgeInsetsMake(6, 0, 0, 0)
      } else {
        let width = (size.width - CGFloat((itemCount + 1)) * ITEM_SPACING) / CGFloat(itemCount)
        layout.itemSize = CGSizeMake(width, width * 10 / 16)
        layout.sectionInset = UIEdgeInsetsMake(ITEM_SPACING, ITEM_SPACING, 0, ITEM_SPACING)
      }
      collectionView?.layoutIfNeeded()
    }
  }