Refresh listbox after adding

I have a listbox in C# and want it to refresh after I added a new item(which gets opened with a new form dialog)

Here is my code which doesn't work.

    private void showAllItems()    {        itemList = Db.getAllItems();        lb_itemList.DataSource = itemList;    }    private void showItemPreview(object sender, EventArgs e)    {        string curItem = lb_itemList.SelectedItem.ToString();        briefPreviewList = Db.getItemBriefPreview(curItem);        string itemInfos = string.Join(",", briefPreviewList.ToArray());        string[] infos = itemInfos.Split(',');        l_itemDB.Text = curItem;        l_CategoryDB.Text = infos[0];    }    private void b_addItem_Click(object sender, EventArgs e)    {        int uid = 1;        AddItem addItemForm = new AddItem(uid);        addItemForm.ShowDialog();        CurrencyManager cm = (CurrencyManager)BindingContext[itemList];        cm.Refresh();    }