MvvmCross 中的动态单元格高度

Question

我想重写 GetHeightForRow 方法，因此当滚动到特定单元格（行）时，我的滚动效果很好。

我发现这个例子here 运行良好。因为这部分代码：

 public override float GetHeightForRow(UITableView tableView, NSIndexPath indexPath)
    {
        if (this.offscreenCell == null)
        {
            this.offscreenCell = new ItemCell();
        }

        var cell = this.offscreenCell;

        cell.UpdateFonts();
        var item = this.model.Items[indexPath.Row];
        cell.Title = item.Title;
        cell.Body = item.Body;

        cell.SetNeedsUpdateConstraints();
        cell.UpdateConstraintsIfNeeded();

        cell.Bounds = new RectangleF(0, 0, this.TableView.Bounds.Width, this.TableView.Bounds.Height);

        cell.SetNeedsLayout();
        cell.LayoutIfNeeded();

        var height = cell.ContentView.SystemLayoutSizeFittingSize(UIView.UILayoutFittingCompressedSize).Height;
        height += 1;

        return height;
    }

尝试将其翻译到我的 MvvmCross 项目中，例如：

public override float GetHeightForRow(UITableView tableView, NSIndexPath indexPath)
    {
        if (this.offscreenCell == null)
        {
            this.offscreenCell = new ItemCell();
        }

        var cell = this.offscreenCell;
        cell.DataContext = this.model.Items[indexPath.Row];

        cell.SetNeedsUpdateConstraints();
        cell.UpdateConstraintsIfNeeded();

        cell.Bounds = new RectangleF(0, 0, this.TableView.Bounds.Width, this.TableView.Bounds.Height);

        cell.SetNeedsLayout();
        cell.LayoutIfNeeded();

        var height = cell.ContentView.SystemLayoutSizeFittingSize(UIView.UILayoutFittingCompressedSize).Height;
        height += 1;

        return height;
    }

但无论如何它总是返回 36.5。有什么制作方法吗？

谢谢你，

Answer 1

使用 UICollectionView 而不是 UITableView 可能会更好。总的来说，它们比表格视图更灵活。

如果你试一试，你会发现为单个项目自定义高度非常容易（集合视图有项目而不是单元格）。

首先，您需要创建一个自定义 UICollectionViewDelegateFlowLayout：

public class ThingDelegateFlowLayout : UICollectionViewDelegateFlowLayout
{
    List<Thing> Things;

    public ThingDelegateFlowLayout(List<Thing> things)
    {
        Things = things;
    }

    // this is the override that allows you to dynamically size UICollectionView items
    public override SizeF GetSizeForItem (UICollectionView collectionView, UICollectionViewLayout layout, NSIndexPath indexPath)
    {
        return new SizeF(
            width: UIScreen.MainScreen.Bounds.Width, // Set the width to whatever you want. In this case, it's the screen width.
            height: Things[indexPath.Row].Height // Set the item height
        );
    }
}

然后在您的视图控制器中执行以下操作。注意重要的一行...

thingCollectionView.Delegate = new ThingDelegateFlowLayout(Things);

...在底部附近，您将自定义 UICollectionViewDelegateFlowLayout 分配给 UICollectionView：

public class ThingViewController : UIViewController
{
    private List<Thing> Things;

    public ThingViewController()
    {
        Things = GetThings();
    }

    // gets a list of sweet hair dos
    private List<Thing> GetThings()
    {
        // do something here to get a sweet list of hair dos
    }

    public override void ViewDidLoad()
    {
        UICollectionViewFlowLayout layout = new UICollectionViewFlowLayout () 
        {
            HeaderReferenceSize = new SizeF(0, 0), // no header
            FooterReferenceSize = new SizeF(0, 0), // no footer
            SectionInset = new UIEdgeInsets(0, 0, 0, 0), // no section inset
            ItemSize = new SizeF(UIScreen.MainScreen.Bounds.Width, 100f), // set each item to the full width of the screen and 100 pixels tall
            ScrollDirection = UICollectionViewScrollDirection.Vertical, // set the collection to scroll vertically
            MinimumInteritemSpacing = 0, // no item spacing
            MinimumLineSpacing = 0, // no line spacing
        };

        var thingCollectionViewController = new UICollectionViewController(layout);
        var thingCollectionView = new UICollectionView(UIScreen.MainScreen.Bounds.Size);

        thingCollectionViewController.CollectionView.Frame = thingCollectionView.Frame;
        thingCollectionView = thingCollectionViewController.CollectionView;
        thingCollectionView.Delegate = new ThingDelegateFlowLayout(Things);
        thingCollectionView.BackgroundColor = UIColor.Clear; // or whatever
        thingCollectionView.BackgroundView = new UIView () 
        {
            BackgroundColor = UIColor.Clear // or whatever
        };

        View.AddSubview (thingCollectionView);
    }
}

我不知道如何使用 UITableView 做到这一点。我基本上已经停止使用表格视图了，因为我更喜欢 UICollectionViews。