In the /NET Assembly, you have to use the DragEnter event as explained here:

• https://www.exontrol.com/sg.jsp?content=support/faq/net/#dragdrop

For /COM components, you can follow the next tutorial  in order to implement the OLE Drag and Drop:

• https://www.exontrol.com/sg.jsp?content=support/faq/all/#dragdrop

The settings for AllowEffects are:

• exOLEDropEffectNone (0), Drop target cannot accept the data, or the drop operation was cancelled
• exOLEDropEffectCopy (1), Drop results in a copy of data from the source to the target. The original data is unaltered by the drag operation.
• exOLEDropEffectMove (2), Drop results in data being moved from drag source to drop source. The drag source should remove the data from itself after the move.

The source component should logically Or together the supported values and places the result in the AllowedEffects parameter. The target component can use this value to determine the appropriate action (and what the appropriate user feedback should be). You may wish to defer putting data into the ExDataObject object until the target component requests it. This allows the source component to save time.  If the user does not load any formats into the ExDataObject, then the drag/drop operation is canceled. Use exCFFiles and Files property to add files to the drag and drop data object.

The idea of drag and drop in exThumbnail control is the same as in other controls. To start accepting drag and drop sources the exThumbnail control should have the OLEDropMode to exOLEDropManual. Once that is is set, the exThumbnail starts accepting any drag and drop sources. 

The first step is if you want to be able to drag items from your exThumbnail control to other controls the idea is to handle the OLE_StartDrag event. The event passes an object ExDataObject (Data) as argument. The Data and AllowedEffects can be changed only in the OLEStartDrag event. The OLE_StartDrag event is fired when user is about to drag items from the control.

The AllowedEffect parameter and SetData property must be set to continue a drag and drop operation.

// OLEStartDrag event is not supported. Use the DragEnter,DragLeave,DragOver, DragDrop ... events.

// OLEStartDrag event is not supported. Use the DragEnter,DragLeave,DragOver, DragDrop ... events.

private void OLEStartDrag(object sender, AxEXTHUMBNAILLib._IThumbnailEvents_OLEStartDragEvent e)
{
}

void OnOLEStartDrag(LPDISPATCH Data,long FAR* AllowedEffects)
{
}

void __fastcall OLEStartDrag(TObject *Sender,Exthumbnaillib_tlb::IExDataObject *Data,long * AllowedEffects)
{
}

procedure OLEStartDrag(ASender: TObject; Data : IExDataObject;var AllowedEffects : Integer);
begin
end;

procedure OLEStartDrag(sender: System.Object; e: AxEXTHUMBNAILLib._IThumbnailEvents_OLEStartDragEvent);
begin
end;

begin event OLEStartDrag(oleobject Data,long AllowedEffects)
end event OLEStartDrag

Private Sub OLEStartDrag(ByVal sender As System.Object, ByVal e As AxEXTHUMBNAILLib._IThumbnailEvents_OLEStartDragEvent) Handles OLEStartDrag
End Sub

Private Sub OLEStartDrag(ByVal Data As EXTHUMBNAILLibCtl.IExDataObject,AllowedEffects As Long)
End Sub

Private Sub OLEStartDrag(ByVal Data As Object,AllowedEffects As Long)
End Sub

LPARAMETERS Data,AllowedEffects

PROCEDURE OnOLEStartDrag(oThumbnail,Data,AllowedEffects)
RETURN

<SCRIPT EVENT="OLEStartDrag(Data,AllowedEffects)" LANGUAGE="JScript">
</SCRIPT>

<SCRIPT LANGUAGE="VBScript">
Function OLEStartDrag(Data,AllowedEffects)
End Function
</SCRIPT>

Procedure OnComOLEStartDrag Variant llData Integer llAllowedEffects
	Forward Send OnComOLEStartDrag llData llAllowedEffects
End_Procedure

METHOD OCX_OLEStartDrag(Data,AllowedEffects) CLASS MainDialog
RETURN NIL

// OLEStartDrag event is not supported. Use the DragEnter,DragLeave,DragOver, DragDrop ... events.

function OLEStartDrag as v (Data as OLE::Exontrol.Thumbnail.1::IExDataObject,AllowedEffects as N)
end function

function nativeObject_OLEStartDrag(Data,AllowedEffects)
return