procedure TfmTemplateOfInventory.Click(Sender: TObject);
begin
StretchHandle1.Detach;
if (Sender is TGroupBox) then
  begin
  perSenderChild:=Sender;      
  StretchHandle1.Attach(Sender as TGroupBox);
  end else
    if (Sender is TEdit) then
      begin
      perSenderChild:=Sender; 
      StretchHandle1.Attach(Sender as TEdit);
      end else
        if (Sender is TLabel) then
          begin
          perSenderChild:=Sender; 
          StretchHandle1.Attach(Sender as TLabel);
          end else
            if (Sender is TCheckBox) then
              begin
              perSenderChild:=Sender; 
              StretchHandle1.Attach(Sender as TCheckBox);
              end else
                if (Sender is TMemo) then
                  begin
                  perSenderChild:=Sender;  
                  StretchHandle1.Attach(Sender as TMemo);
                  end ;
end;

procedure WndProc(var Message: TMessage); override;

procedure TfmTemplateOfInventory.WndProc(var Message: TMessage);
var
  MousePoint: TPoint;
  WndHnd: THandle;
  aName: array [0..255] of Char; 
begin
  with Message do
    case Msg of

      CM_MOUSELEAVE:
        begin
          GetCursorPos(MousePoint);
          WndHnd := WindowFromPoint(MousePoint);
          Label8.Caption:= IntToStr( WndHnd);
          GetClassName(WndHnd, aName, 256)   ;
          Label10.Caption:=  aName;
        end;

      CM_MOUSEENTER:
        begin
        GetCursorPos(MousePoint);
        WndHnd := WindowFromPoint(MousePoint);
        Label9.Caption:= IntToStr( WndHnd);
        end;
    end;
  inherited WndProc(Message);
end;

type
  TMyComboBox = class(StdCtrls.TComboBox)
  private
    procedure WMLBUTTONDOWN(var msg: TMessage); message WM_LBUTTONDOWN;
end; 



type
  TfmTemplateOfInventory = class(TForm)
//....

  private
    procedure WndProc(var Message: TMessage); override;

var
   perSenderChild: TObject
   MousePoint: TPoint; 
end;


//тут получаем координаты курсора на форме 
procedure TfmTemplateOfInventory.WndProc(var Message: TMessage);
var
  WndHnd: THandle;
begin
  with Message do
    case Msg of

      CM_MOUSELEAVE:
        begin
          GetCursorPos(MousePoint);
          WndHnd := WindowFromPoint(MousePoint);
        end;
    end;
  inherited WndProc(Message);
end;


procedure TMyComboBox.WMLBUTTONDOWN(var msg: TMessage);
begin
inherited;
  case msg.Msg of
    WM_LBUTTONDOWN:
      begin
      fmTemplateOfInventory.StretchHandle1.Detach;
      fmTemplateOfInventory.StretchHandle1.Attach(FindDragTarget(MousePoint,true));
      perSenderChild:=FindDragTarget(MousePoint,true);
      end
  end;
end;