UNIT Unit3;
INTERFACE
USES
   Winapi.Windows, Winapi.Messages, System.SysUtils, System.Variants, System.Classes, Vcl.Graphics,
   Vcl.Controls, Vcl.Forms, Vcl.Dialogs;
type
   TForm3 = class(TForm)
   private
      procedure WMSYSCOMMAND(var Msg: TWMSYSCOMMAND); message WM_SYSCOMMAND;
      procedure WMACTIVATEAPP(var Msg: TWMACTIVATEAPP); message WM_ACTIVATEAPP;
   public
   end;
var
  Form3: TForm3;

IMPLEMENTATION
{$R *.dfm}
uses Unit1;

procedure TForm3.WMSYSCOMMAND(var Msg: TWMSYSCOMMAND);
begin
   if (Application.MainForm.Handle>0) and (Msg.CmdType=SC_MINIMIZE) then begin
      ShowWindow(Form1.Handle, SW_SHOW);
      ShowWindow(Application.MainForm.Handle, SW_MINIMIZE);
   end;
   inherited;
end;

procedure TForm3.WMACTIVATEAPP(var Msg: TWMACTIVATEAPP);
begin
   if IsIconic(Application.MainForm.Handle) then begin
      ShowWindow(Form1.Handle, SW_HIDE);
      ShowWindow(Application.MainForm.Handle, SW_RESTORE);
   end;
   inherited;
end;

END.