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procedure TForm1.FormShow(Sender: TObject);
begin
Form1.WindowState:= wsMaximized;
end;					

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function getHeightOfTaskBar : integer;
var hTaskBar:HWND;
    rect : TRect;
begin
     hTaskbar := FindWindow('Shell_TrayWnd', Nil);
     if hTaskBar<>0 then
        GetWindowRect(hTaskBar, rect);

     Result:=rect.bottom - rect.top;
end;

procedure Maximizer; 
begin
    if Form1.WindowState=wsNormal then
       begin
        Form1.WindowState:=wsMaximized;
        Form1.SetBounds(0,0,screen.Width,screen.Height-getHeightOfTaskBar);
       end
       else
       begin
         Form1.WindowState:=wsNormal;
       end;

   //    ShowTrayWindow;
end;