private struct ContextMenuActionKey
{
    public const string Add = "Add";
}

public void OnContextMenuItemClicked(object sender, ToolStripItemClickedEventArgs e)
{
    var actionKey = Convert.ToString(e.ClickedItem.Tag);

    switch (actionKey)    
    {
        case ContextMenuActionKey.Add:
            newForm f = new newForm(BindingSource);
            f.ShowDialog();
            break;
    }
}

public void OnViewMouseUp(object sender, MouseEventArgs e)
{
    var contexMenu = new ContextMenuStrip();

    if (e.Button == MouseButtons.Left)
    {
        return;
    }

    ToolStripItem item = contexMenu.Items.Add("Добавить");
    
    item.Enabled = true;
    item.Tag = ContextMenuActionKey.Add;

    contexMenu.Show(Control.MousePosition);
    contexMenu.ItemClicked += OnContextMenuItemClicked;
}

Item.Click += new System.EventHandler(AddMenuStripClick);