private void openFile()
        {
            OpenFileDialog openFileDialog = new OpenFileDialog();

            openFileDialog.Filter = "Програма за артикли (*.atk)|*.atk";
            openFileDialog.Title  = "Отвори ја програмата";
            if (openFileDialog.ShowDialog() == DialogResult.OK)
            {
                FileName = openFileDialog.FileName;
                try
                {
                    using (FileStream fileStream = new FileStream(FileName, FileMode.Open))
                    {
                        IFormatter formater = new BinaryFormatter();
                        SaveDoc = (SaveDoc)formater.Deserialize(fileStream);
                    }
                }
                catch (Exception ex)
                {
                    MessageBox.Show("Could not read file: " + FileName);
                    FileName = null;
                    return;
                }
                Invalidate(true);
            }
        }
        public Form1()
        {
            InitializeComponent();
            SaveDoc = new SaveDoc();
            Category category = new Category("Алат", 1);

            category.AddProduct(new Product("Клешта", 10));
            lbKategorii.Items.Add(category);
            Category category2 = new Category("Електричен алат", 2);

            category2.AddProduct(new Product("Бруска", 15));
            lbKategorii.Items.Add(category2);
            loadCategory();
        }
 private void newToolStripButton_Click(object sender, EventArgs e)
 {
     SaveDoc = new SaveDoc();
     Invalidate(true);
 }