UICollectionView：最后一行项目之间不需要的空格

Question

我希望我的细胞像这样显示

X
Group 1
X X X
X X
Group 2
X X X
X X X

但是，这是我得到的输出。我不期望名为Home的单元格在中心对齐，也不期望第二行Employee通信中间的空间。

private class MenuDelegate : UICollectionViewDelegateFlowLayout
{

    private const int interItemSpacing = 12;

    private readonly double _itemWidth;
    private readonly double _itemsPerRow;

    private readonly List<MenuItem> _items;


    public MenuDelegate(List<MenuItem> items)
    {
        _items = items;
        _itemsPerRow = DisplayUtils.IsIPad ? 5 : 3;
        _itemWidth = (PlatformConstants.MenuWidth - ((_itemsPerRow - 1) * interItemSpacing)) / _itemsPerRow;
    }

    public override CGSize GetSizeForItem(UICollectionView collectionView,
                                              UICollectionViewLayout layout, NSIndexPath indexPath)
    {
        if (_items[indexPath.Row].Parent) {
            return new CGSize(DisplayUtils.ScreenWidth, 44);
        }
        return new CGSize(_itemWidth, _itemWidth);
    }

    public override void ItemSelected(UICollectionView collectionView, NSIndexPath indexPath)
    {
        HandleCellSelect(_items[indexPath.Row]);
    }

    public override nfloat GetMinimumInteritemSpacingForSection(UICollectionView collectionView, UICollectionViewLayout layout, nint section)
    {
        return interItemSpacing;
    }

    public override nfloat GetMinimumLineSpacingForSection(UICollectionView collectionView, UICollectionViewLayout layout, nint section)
    {
        return float.Epsilon;
    }
}

Answer 1

您是否尝试在自定义LayoutAttributesForElementsInRect中重写UICollectionViewFlowLayout并设置属性。这发生在UICollectionViewFlowLayout为单个单元格返回2个属性时。

public class CustomFlowLayout : UICollectionViewFlowLayout
    {
        public override UICollectionViewLayoutAttributes[] LayoutAttributesForElementsInRect(CGRect rect)
        {
            UICollectionViewLayoutAttributes[]  attributes = base.LayoutAttributesForElementsInRect(rect);
            UICollectionViewLayoutAttributes[]  newAttributes = new UICollectionViewLayoutAttributes[attributes.Length];
            foreach (UICollectionViewLayoutAttributes attribute in attributes)
            {
                if ((attribute.Frame.X + attribute.Frame.Width<= this.CollectionViewContentSize.Width) &&
                    (attribute.Frame.Y + attribute.Frame.Height <= this.CollectionViewContentSize.Height))
                {
                    newAttributes.Append(attribute);
                }
            }
            return newAttributes;
        }

    }

有关详细信息，请查看here

Answer 2

我有一个子类UICollectionViewFlowLayout来实现所需的结果。

private class CustomFlowLayout : UICollectionViewFlowLayout
{
    public override UICollectionViewLayoutAttributes[] LayoutAttributesForElementsInRect(CGRect rect)
    {
        var attributes = base.LayoutAttributesForElementsInRect(rect);

        var leftMargin = SectionInset.Left;
        var maxY = 2.0f;

        var horizontalSpacing = 6f; // spacing between the items.

        foreach (var attribute in attributes) {
            if (attribute.Frame.Y >= maxY || attribute.Frame.X == SectionInset.Left) {
                leftMargin = SectionInset.Left;
            }
            if (attribute.Frame.X == SectionInset.Left)
                leftMargin = SectionInset.Left;
            else
                attribute.Frame = new CGRect(leftMargin, attribute.Frame.Y, attribute.Frame.Width, attribute.Frame.Height);

            leftMargin += attribute.Frame.Width + horizontalSpacing;
            maxY = (float)Math.Max(attribute.Frame.GetMaxY(), maxY);
        }

        return attributes;
    }
}