ios - 尝试在 UICollectionView 中显示标题时未调用 GetViewForSupplementaryElement

Question

我正在尝试设置 UICollectionView在我现有的UIViewController 中.除了为每个部分显示一个标题外，一切正常 - 我无法弄清楚我做错了什么。

我在 UIViewController 中的代码启动 Collection View :

public partial class ViewController : UIViewController
{
    //...

    public override void ViewDidLoad ()
    {
        base.ViewDidLoad ();

        CollectionView_Outlet.RegisterClassForCell(typeof(ModifierCell), ModifierCell.CellID);
        CollectionView_Outlet.RegisterClassForSupplementaryView (typeof(Header), UICollectionElementKindSection.Header, Header.HeaderId);
        CollectionView_Outlet.ShowsHorizontalScrollIndicator = false;
        CollectionView_Outlet.Source = new ModifiersSource(this);
        CollectionView_Outlet.BackgroundColor = UIColor.White;
        CollectionView_Outlet.ReloadData();
    }

    //...
}

然后我创建了 UICollectionViewSource 的子类:

public class ModifiersSource : UICollectionViewSource
{
    ViewController senderVC;

    public ModifiersSource(ViewController sender)
    {
        senderVC = sender;
    }

    public override nint NumberOfSections(UICollectionView collectionView)
    {
        return 2;
    }

    public override nint GetItemsCount (UICollectionView collectionView, nint section)
    {
        return senderVC.modifiers.Count;
    }

    public override UICollectionViewCell GetCell(UICollectionView collectionView, NSIndexPath indexPath)
    {
        //...
    }


    public override UICollectionReusableView GetViewForSupplementaryElement(UICollectionView collectionView, NSString elementKind, NSIndexPath indexPath)
    {
        var headerView = (Header)collectionView.DequeueReusableSupplementaryView (elementKind, Header.HeaderId, indexPath);
        headerView.Text = "Supplementary View";
        return headerView;  
    }

}

最后创建:

public class Header : UICollectionReusableView
{
    public static NSString HeaderId = new NSString("UserSource1");
    UILabel label;

    public string Text {
        get {
            return label.Text;
        }
        set {
            label.Text = value;
            SetNeedsDisplay ();
        }
    }

    [Export ("initWithFrame:")]
    public Header (RectangleF frame) : base (frame)
    {
        label = new UILabel (){
            Frame = new RectangleF(0,0,300,50), 
            BackgroundColor = UIColor.Red};
        AddSubview (label);
        BackgroundColor = UIColor.White;
    }
}

我在 GetViewForSupplementaryElement 上放了一个断点方法，但它永远不会被调用。我还在 StoryBoard 中设置了以下内容:



我错过了什么？!

Answer 1

在多次尝试无法使上述工作后，我手动设置 UICollectionViewFlowLayout同时启动 UIContainerView .似乎成功了，但不知道为什么它没有从我的 StoryBoard 中获取设置.这是我的工作代码:

public override void ViewDidLoad ()
    {
        base.ViewDidLoad ();

        CollectionView_Outlet.RegisterClassForCell(typeof(ModifierCell), ModifierCell.CellID);
        CollectionView_Outlet.RegisterClassForCell(typeof(ItemOptionCell), ItemOptionCell.CellID);
        CollectionView_Outlet.RegisterClassForSupplementaryView (typeof(Header), UICollectionElementKindSection.Header, Header.HeaderId);
        CollectionView_Outlet.ShowsHorizontalScrollIndicator = false;

        //This is the new bit I added:
        var layout = new UICollectionViewFlowLayout ();
        layout.HeaderReferenceSize = new CGSize (300, 40);
        CollectionView_Outlet.SetCollectionViewLayout (layout, false);

        CollectionView_Outlet.Source = new ModifiersSource(this);
        CollectionView_Outlet.ReloadData();
    }