AutoCAD 2027 Drag-Drop Fixed in Update 1

When AutoCAD 2027 was first released with .NET 10 support, many developers encountered a critical regression: drag-and-drop operations from custom palettes to the drawing area would crash with an InvalidCastException.

System.InvalidCastException: Unable to cast COM object of type 'System.__ComObject'
to interface type 'System.Windows.Forms.IDataObject'.
QueryInterface call failed with E_NOINTERFACE (0x80004002).

What Caused It?

This was a compatibility issue introduced by breaking changes in .NET 9 (which carried over into .NET 10):

• PR dotnet/winforms#10759 changed how Control.DoDragDrop() wraps data objects.
• System.Windows.Forms.IDataObject lost its COM visibility in .NET 5 (PR #3388).
• AutoCAD’s internal drag-and-drop handler was no longer able to cast the COM object.

Affected Versions

• AutoCAD 2024–2026 (.NET Framework 4.8 / .NET 8) — Worked fine
• AutoCAD 2027 RTM (.NET 10) — Broken

Reproducing the Issue

The following minimal palette/command reproduces the crash. Starting a drag from the list box and dropping it onto the drawing area throws the InvalidCastException shown above on AutoCAD 2027 RTM:

public class ExtensionApplication : IExtensionApplication
{
    public void Initialize()
    {
        // Initialization code if needed
    }
    public void Terminate()
    {
        // Cleanup code if needed
    }
}

public class DragDropTestCommand
{
    static PaletteSet s_paletteSet;

    [CommandMethod("DRAGDROPTEST")]
    public void ShowDragDropPalette()
    {
        if (s_paletteSet == null)
        {
            s_paletteSet = new PaletteSet("DragDrop PoC",
                new Guid("A1B2C3D4-E5F6-7890-ABCD-EF1234567890"))
            {
                Style = PaletteSetStyles.ShowCloseButton
                                   | PaletteSetStyles.ShowAutoHideButton,
                MinimumSize = new System.Drawing.Size(200, 150)
            };

            var host = TestDragPalette.CreateControl();
            s_paletteSet.Add("Drag Items", host);
        }

        s_paletteSet.Visible = true;
    }
}

public sealed class TestDropTarget : DropTarget
{
    public override void OnDrop(DragEventArgs e)
    {
        var doc = AcadApp.DocumentManager.MdiActiveDocument;
        doc?.Editor.WriteMessage("\nTestDropTarget.OnDrop reached — drop succeeded.\n");
    }
}

public static class TestDragPalette
{
    static Point _dragStart;
    const double DragThreshold = 5.0;

    public static System.Windows.Forms.Control CreateControl()
    {
        var listBox = new ListBox { SelectionMode = SelectionMode.Single };
        listBox.Items.Add("Asset A");
        listBox.Items.Add("Asset B");
        listBox.Items.Add("Asset C");
        listBox.PreviewMouseLeftButtonDown += (s, e) =>
        {
            _dragStart = e.GetPosition(listBox);
        };
        listBox.PreviewMouseMove += (s, e) =>
        {
            if (e.LeftButton != MouseButtonState.Pressed)
                return;
            var pos = e.GetPosition(listBox);
            if (System.Math.Abs(pos.X - _dragStart.X) < DragThreshold &&
                System.Math.Abs(pos.Y - _dragStart.Y) < DragThreshold)
                return;
            if (listBox.SelectedItem == null)
                return;
            // This call reproduces the crash.
            // AutoCAD internally casts the OLE IDataObject to
            // System.Windows.Forms.IDataObject, which fails on .NET 8+
            // because that interface is no longer COM-visible.
            using (var button = new System.Windows.Forms.Button())
            {
                Autodesk.AutoCAD.ApplicationServices.Application.DoDragDrop(
                    button,
                    listBox.SelectedItem,
                    System.Windows.Forms.DragDropEffects.All,
                    new TestDropTarget());
            }
        };
        var host = new ElementHost { Child = listBox, Dock = System.Windows.Forms.DockStyle.Fill };
        return host;
    }
}

The Fix

Autodesk resolved the InvalidCastException reproduced above in AutoCAD 2027 Update 1 — the drag-and-drop path in the example works again after installing the update.

Custom-Type Drag Payloads and BinaryFormatter

Reader Norman Yuan flagged that Update 1 doesn’t cover every drag-and-drop scenario: code that passes a custom object through IDataObject.SetData(Type, object) still fails on 2027.1 — not with an exception this time, but silently. e.Data.GetFormats() correctly lists the custom type’s format, yet e.Data.GetData(typeof(T)) comes back null.

This is a separate issue from the one this post covers, and it’s out of scope for AutoCAD to fix directly. SetData/GetData for non-native types relied on BinaryFormatter to marshal the payload across the OLE/COM boundary, and BinaryFormatter is removed by default starting .NET 9/10 — a deliberate Microsoft security decision, not an AutoCAD regression. Update 1’s fix was intentionally scoped to the exception reproduced above; it was never going to restore BinaryFormatter-based marshaling.

See Microsoft’s guidance on migrating off BinaryFormatter: BinaryFormatter migration guide.

The fix is straightforward: don’t hand a custom object to SetData at all — serialize it yourself and pass a string instead. Strings marshal natively across the OLE boundary and never touch the broken path:

// Before — relies on BinaryFormatter, silently returns null on 2027.1
IDataObject dataObject = new DataObject();
dataObject.SetData(typeof(CircleInfo), circle);
...
var data = e.Data.GetData(typeof(CircleInfo));   // always null

// After — JSON round-trip, confirmed working on AutoCAD 2027 Update 1
string json = JsonSerializer.Serialize(payload);
dataObject.SetData(typeof(string), json);
...
var json = e.Data.GetData(typeof(string)) as string;
var payload = JsonSerializer.Deserialize<TPayload>(json);

The same approach is behind Norman’s own published workaround. If you’d rather use the built-in .NET 10 equivalent instead of rolling your own JSON step, see Clipboard.SetDataAsJson<T>() / Clipboard.TryGetData<T>().

Download the Fix

You can download the update directly from the Autodesk Portal:

Download AutoCAD 2027 Update 1

After the Fix

The repro command above, running on AutoCAD 2027 Update 1: