阻止form移动到桌面以外

    procedure FormMove(var Msg: TWMMove); message WM_MOVE;

procedure TForm1.FormMove(var Msg: TWMMove);
var
  WorkArea: TRect;
begin
  inherited;
  if SystemParametersInfo(SPI_GETWORKAREA, 0, @WorkArea, 0) then
  begin
    if Left < WorkArea.Left then
      Left := WorkArea.Left
    else if Left + Width > WorkArea.Right then
      Left := WorkArea.Right - Width;
    if Top < WorkArea.Top then
      Top := WorkArea.Top
    else if Top + Height > WorkArea.Bottom then
      Top := WorkArea.Bottom - Height;
  end;
end;