Drag And Drop

See the DragAndDropDemo.cs.

using Gridrand.Contracts;
using System;
namespace Gridrand.RimGui.Manual
{
    /// <summary>
    /// Drag and drop demo.
    /// </summary>
    class DragDropDemo : ManualBase, IManual
    {
        string[] names = new string[3] { "A", "B", "C", };

        public DragDropDemo(ManualBaseResource p) : base(p)
        {
        }

        public void Draw()
        {
            using var spaceScope = Style.SpacingYs.Begin(0f);
            for (int i = 0; i < names.Length; i++)
            {
                using var s = Ctx.PushId(i);

                DrawInsertArea(i);

                // Drag target.
                // Any interactive widget, like a Button, will work.
                Gui.InteractiveItem();

                //Mark the last widget as a drop target.
                Ctx.MarkLastDropTarget("Key");

                // Try dragging the last widget.
                var isDraggedItem = Ctx.TryDragLast("Key", i);

                Gui.NextRect(Ctx.GetLastWidgetRect()).Text($"{names[i]}");

                if (isDraggedItem)
                {
                    if (Gui.BeginAutoSizeSubWindow("DragInfo"))
                    {
                        Gui.FixedWidthText(names[i]);
                        Gui.EndAutoSizeSubWindow();
                    }
                }

                /// By marking the drop target with<see cref= "Context.MarkLastDropTarget(string)" />, 
                /// you can drop it with <see cref="Context.TryDrop(string, out object)"/>().
                if (Ctx.TryDrop("Key", out var payload))
                {
                    var tmp = names[i];
                    names[i] = names[(int)payload];
                    names[(int)payload] = tmp;

                    Logger.Debug($"Dropped:{i},{payload}");
                }
            }
            DrawInsertArea(names.Length);
        }

        void DrawInsertArea(int insertI)
        {
            if (names.Length < insertI)
                throw new ArgumentOutOfRangeException($"{insertI}");

            var widget = Gui.NextHeight(20f).Custom<InsertAreaWidget>(true);

            /// Attempt to mark the drop target to the rect of <see cref="InsertAreaWidget"/>.
            Ctx.MarkDropTarget("Key", Ctx.GetLastWidgetRect());

            widget.Color = Ctx.CanDrop("Key") ? Color32.Green : Color32.Gray;

            /// Try insertion.
            if (Ctx.TryDrop("Key", out var payload))
            {
                var insertArrayI = (int)payload < insertI ? insertI - 1 : insertI;
                Logger.Debug($"{payload} was dropped and inserted into {insertArrayI}.");
                names.Move((int)payload, insertArrayI);
            }
        }

        class InsertAreaWidget : PrimitiveWidget
        {
            public Color32 Color { get; set; } = Color32.Green;

            public override void Build(Shaper shaper)
            {
                shaper.AddInnerFrameRect(Rect, 1f, Color);
            }
        }
    }
}