{
 The following example demonstrates the Drag&Drop machanism from an external
 application (Wordpad, Microsoft,..) to a TMemo in your own application.
 }
unit TMemoDragDropFrm;
{ ****************************************************************
 Source File Name : TMemoDragDropFrm.pas
 Typ : Hauptformular
 Autor : Andreas Kosch
 Compiler : Delphi 4.02 CSS
 Betriebssystem : Windows 98
 Beschreibung : Text via OLE Drag&Drop ubernehmen aus einer
  anderen Anwendung (wie zum Beispiel WordPad)
  ubernehmen.
 16.01.2003: Test mit Delphi 7 und Microsoft Word XP unter Windowx XP
 **************************************************************** }
 { Comments by Thomas Stutz }
interface
uses
 Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
 Dialogs, ComCtrls, ActiveX, ShlObj, ComObj, StdCtrls;
type
 // TForm1's declaration indicates that it's a TForm and that
 // it supports the IDropTarget interface:
 {
 IDropTarget
 Any application wanting to accept drop operations must
 implement the IDropTarget interface.
 Methods of the IDropTarget interface:
 DragEnter
  Dragged item has just been moved into the application's window,
  return the relevant icon.
 DragOver
  Dragged item is being moved over the application's window,
  return the relevant icon.
 DragLeave
  Dragged item has just moved out of the application's window.
 Drop
  The dragged item has been dropped on this application.
 }
 TForm1 = class(TForm, IDropTarget)
  Memo1: TMemo;
  procedure FormCreate(Sender: TObject);
  procedure FormDestroy(Sender: TObject);
 private
  // IDropTarget
  function DragEnter(const dataObj: IDataObject;
  grfKeyState: Longint;
  pt: TPoint;
  var dwEffect: Longint): HResult; stdcall;
  function DragOver(grfKeyState: Longint;
  pt: TPoint;
  var dwEffect: Longint): HResult; stdcall;
  function DragLeave: HResult; stdcall;
  function Drop(const dataObj: IDataObject;
  grfKeyState: Longint; pt: TPoint;
  var dwEffect: Longint): HResult; stdcall;
  // IUnknown
  // Ignore referance counting
  function _AddRef: Integer; stdcall;
  function _Release: Integer; stdcall;
 public
 end;
var
 Form1: TForm1;
implementation
{$R *.dfm}
uses
 ShellAPI;

// In the OnCreate event handler, two important methods are called.
// First, OleInitalize is called. This initializes the OLE libraries and should always be
// called before your application uses any OLE functions.
// RegisterDragDrop registers the window as a valid drop target.
// If this isn't called, the window will never receive any drop events.

procedure TForm1.FormCreate(Sender: TObject);
begin
 OleInitialize(nil);
 {Allow window to accept drop events}
 OleCheck(RegisterDragDrop(Handle, Self));
 { Execute Wordpad for testing }
 ShellExecute(Handle, 'open', 'wordpad', 'c:\Test.doc', nil, SW_SHOW);
end;
// OnDestroy does the exact opposite. It calls RevokeDropTarget to indicate that
// drop events are no longer accepted.
// It then calls OleUninitialize, since the application is finished using all OLE functions.
procedure TForm1.FormDestroy(Sender: TObject);
begin
 {Finished accepting drops}
 RevokeDragDrop(Handle);
 OleUninitialize;
end;
{-----------------------------------------------------------------}
{ IDropTarget-Implementierung }
{-----------------------------------------------------------------}
function TForm1.DragEnter(const dataObj: IDataObject;
 grfKeyState: Longint;
 pt: TPoint;
 var dwEffect: Longint): HResult;
begin
 dwEffect := DROPEFFECT_COPY;
 Result := S_OK;
end;
function TForm1.DragOver(grfKeyState: Longint;
 pt: TPoint;
 var dwEffect: Longint): HResult;
begin
 dwEffect := DROPEFFECT_COPY;
 Result := S_OK;
end;
function TForm1.DragLeave: HResult;
begin
 Result := S_OK;
end;
function TForm1._AddRef: Integer;
begin
  Result := 1;
end;
function TForm1._Release: Integer;
begin
  Result := 1;
end;
function TForm1.Drop(const dataObj: IDataObject;
 grfKeyState: Longint;
 pt: TPoint;
 var dwEffect: Longint): HResult;
var
 aFmtEtc: TFORMATETC;
 aStgMed: TSTGMEDIUM;
 pData: PChar;
begin
 {Make certain the data rendering is available}
 if (dataObj = nil) then
  raise Exception.Create('IDataObject-Pointer is not valid!');
 with aFmtEtc do
 begin
  cfFormat := CF_TEXT;
  ptd := nil;
  dwAspect := DVASPECT_CONTENT;
  lindex := -1;
  tymed := TYMED_HGLOBAL;
 end;
 {Get the data}
 OleCheck(dataObj.GetData(aFmtEtc, aStgMed));
 try
  {Lock the global memory handle to get a pointer to the data}
  pData := GlobalLock(aStgMed.hGlobal);
  { Replace Text }
  Memo1.Text := pData;
 finally
  {Finished with the pointer}
  GlobalUnlock(aStgMed.hGlobal);
  {Free the memory}
  ReleaseStgMedium(aStgMed);
 end;
 Result := S_OK;
end;
end.