var
  User32ModH: HMODULE;
  SetLayeredWindowAttributes: TSetLayeredWindowAttributes = nil;

procedure ShowDropBin(Sender: TMenuItem);
begin
  if Assigned(frmDropBin) then frmDropBin.Close
  else begin
    frmDropBin := TfrmDropBin.CreateParented(GetDesktopWindow);
  end;
end;

constructor TfrmDropBin.Create(AOwner: TComponent);
begin
  inherited Create(AOwner);
  Width := 32;
  Height := 32;
end;

procedure TfrmDropBin.CreateParams(var Params: TCreateParams);
begin
  inherited CreateParams(Params);
  with Params do begin
    Style := WS_POPUP or WS_CLIPSIBLINGS {or WS_BORDER};
    ExStyle := WS_EX_TOOLWINDOW or WS_EX_TOPMOST;
  end;
end;

procedure TfrmDropBin.CreateWnd;
begin
  inherited CreateWnd;
  Visible := True;
  // 为 2000/XP 创建半透明、穿透效果
  if Assigned(SetLayeredWindowAttributes) then begin
    SetWindowLong(Handle, GWL_EXSTYLE, GetWindowLong(Handle, GWL_EXSTYLE) or WS_EX_LAYERED);
    SetLayeredWindowAttributes(Handle, clWhite, 128, LWA_ALPHA or LWA_COLORKEY);
  end;
  // 设置为接受拖拽
  OleCheck(RegisterDragDrop(Handle, Self));
end;

procedure TfrmDropBin.DestroyWnd;
begin
  if HandleAllocated then RevokeDragDrop(Handle);
  inherited DestroyWnd;
end;

function TfrmDropBin.DragEnter(const dataObj: IDataObject; grfKeyState: Longint; pt: TPoint; var dwEffect: Longint): HResult; stdcall;
begin
  //
  // 也可以在此判断是否接受拖拽,修改 dwEffect 可以得到不同的效果
  //
  dwEffect := DROPEFFECT_COPY;
  Result := S_OK;
end;

function TfrmDropBin.IDropTarget_DragOver(grfKeyState: Longint; pt: TPoint; var dwEffect: Longint): HResult; stdcall;
begin
  dwEffect := DROPEFFECT_COPY;
  Result := S_OK;
end;

function TfrmDropBin.DragLeave: HResult; stdcall;
begin
  Result := S_OK;
end;

function TfrmDropBin.Drop(const dataObj: IDataObject; grfKeyState: Longint; pt: TPoint; var dwEffect: Longint): HResult; stdcall;
begin
  //
  // 处理 dataObj 中包含的拖拽内容
  //
  dwEffect := DROPEFFECT_NONE;
  Result := S_OK;
end;

procedure TfrmDropBin.DoClose(var Action: TCloseAction);
begin
  Action := caFree;
  frmDropBin := nil;
end;

procedure TfrmDropBin.WMNCHitTest(var Msg:TWMNCHitTest);
begin
  // 通过 Client 区拖动窗口
  DefaultHandler(Msg);
  if Msg.Result = HTCLIENT then
  Msg.Result:= HTCAPTION;
end;

initialization
  OleInitialize(nil);
  // 为兼容 Win9x
  User32ModH := GetModuleHandle(''User32.dll'');
  if User32ModH <> 0 then @SetLayeredWindowAttributes := GetProcAddress(User32ModH, ''SetLayeredWindowAttributes'');

finalization
  OleUninitialize;
 
end.