private void SetDataSources() { var allProducts = ProductOperations.GetAll()?.ItemList ?? new List <ProductDto>(); var branchProducts = ddlBranches.SelectedValue == "0" ? new List <ProductDto>() : ProductOperations.GetAllByStoreId(int.Parse(ddlBranches.SelectedValue)); RadListBoxSource.DataSource = branchProducts.Count > 0 ? allProducts.Where(p => !branchProducts.Contains(p)) : allProducts; RadListBoxSource.DataBind(); RadListBoxDestination.DataSource = branchProducts; RadListBoxDestination.DataBind(); }