Tree

See the TreeDemo class.

public void Draw()
{
    Gui.Heading("Scroll");
    {
        Gui.NextHeight(Size.Fixed(150f));
        // Render a scrollable tree.
        if (Gui.BeginScroll())
        {
            //note:By holding down the Alt key while clicking Foldout, you can open / close all child elements.
            Gui.Tree(scrollRoots, new(nodeDrawer, scrollSelection, nodeHandler), Ctx.GetWidgetRect());

            Gui.EndScroll();
        }
    }

    Gui.Heading("FixedScrollTree");
    {
        // Render a fixed-size scrollable tree.
        Gui.FixedScrollTree(150, fixedScrollRoots, new(nodeDrawer, fixedScrollSelection, nodeHandler));
    }
}

/// <summary>
/// Represents a node in the tree structure.
/// </summary>
class Node
{
    public bool IsCheck { get; set; }
    public string Name { get; set; }
    public List<Node> Children { get; } = new();
    public bool HasChild => 0 < Children.Count;
}

/// <summary>
/// Handles rendering of tree nodes.
/// </summary>
class NodeDrawer : ITreeNodeDrawer<Node>
{
    readonly Gui ui;

    public NodeDrawer(Gui ui)
    {
        this.ui = ui;
    }

    /// <summary>
    /// Draws a tree node.
    /// </summary>
    /// <param name="node">The node to draw.</param>
    /// <param name="rect">The rectangle area allocated for the node.</param>
    public void Draw(Node node, Rect rect)
    {
        using var rects = ui.RectsBuilder.Fixed(rect.height).Fit(1).BuildHorizontal(rect);
        var isCheck = node.IsCheck;
        ui.NextRect(rects.R0).CheckBox(ref isCheck);
        node.IsCheck = isCheck;
        ui.NextRect(rects.R1).Text(node.Name);
    }
}

/// <summary>
/// Handles tree node interactions, such as expanding and selecting nodes.
/// </summary>
class NodeHandler : NodeHandlerBase<Node>
{
    public NodeHandler(InputContext input) : base(input)
    {
    }
    public override IEnumerable<Node> GetChildren(Node node) => node.Children;
}