Drag&Drop拖放支持

{
 Das folgende Beispiel demonstriert der Drag&Drop Maechanismus
 aus externen Anwendungen (wie zum Beispiel WordPad oder Microsoft Word)
 in ein TMemo des eigenen Delphi-Programms.
}
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 übernehmen aus einer
  anderen Anwendung (wie zum Beispiel WordPad)
  übernehmen.
  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
        { Private declarations }
        // 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
        { Public declarations }
    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.