Problem with pre-select values on PostBack

[Sebastien Veilleux]

We are using the multiselect control with values pre-selection and ToDataSourceResult instance as describe in documentation.

Unfortunately, when we post our model and its ModelState is invalid, we return to the view and the control fails to display the pre-selection and the search also stop working.

Here is some sample snippet.

Model

public class CreateModel
{
    [Required]
    public string Name { get; set; }

    public List<int> ProductIds { get; set; }
    public List<Product> InitialProducts { get; set; }
}

public class Product
{
    public int ProductId { get; set; }
    public string ProductName { get; set; }
}

Controller

public class HomeController : Controller
{
    [HttpGet]
    public ActionResult Create()
    {
        var initialProduct = GetProductList().First();

        var model = new CreateModel
        {
            InitialProducts = new List<Product>(new[] { initialProduct }),
            ProductIds = new List<int>(new[] { initialProduct.ProductId })
        };

        return View(model);
    }

    [HttpPost]
    public ActionResult Create(CreateModel model)
    {
        if (ModelState.IsValid)
            return RedirectToAction("Success");

        model.InitialProducts = GetProductList().Where(p => model.ProductIds.Contains(p.ProductId)).ToList();

        return View(model);
    }

    [HttpGet]
    public ActionResult Success()
    {
        return View();
    }

    private static IEnumerable<Product> GetProductList()
    {
        return new[]
        {
            new Product { ProductId = 1, ProductName = "Chai" },
            new Product { ProductId = 2, ProductName = "Chang" },
            new Product { ProductId = 3, ProductName = "Book" },
            new Product { ProductId = 4, ProductName = "Fork" },
            new Product { ProductId = 5, ProductName = "Knife" },
            new Product { ProductId = 6, ProductName = "Spoon" },
            new Product { ProductId = 7, ProductName = "Dish" },
            new Product { ProductId = 8, ProductName = "Glass" },
            new Product { ProductId = 9, ProductName = "Cup" }
        };
    }

    [HttpPost]
    public JsonResult GetDataSourceProducts([DataSourceRequest] DataSourceRequest request)
    {
        var products = GetProductList();

        if (request.Filters != null && request.Filters.Count > 0)
        {
            var filter = (FilterDescriptor)request.Filters[0];
            products = products.Where(p => p.ProductName.ToLower().Contains((string)filter.Value)).AsEnumerable();
        }

        return Json(products.ToDataSourceResult(request), JsonRequestBehavior.AllowGet);
    }
}

View

@using (Html.BeginForm("Create", "Home"))
{
    <div>
        @Html.Kendo().TextBoxFor(m => m.Name)
        @Html.ValidationMessageFor(m => m.Name)
    </div>

    <div>
        @(Html.Kendo().MultiSelectFor(m => m.ProductIds)
              .DataTextField("ProductName")
              .DataValueField("ProductId")
              .Placeholder("Select products...")
              .AutoBind(false)
              .DataSource(source => source
                  .Custom()
                  .ServerFiltering(true)
                  .Type("aspnetmvc-ajax")
                  .Transport(transport => transport.Read(read => read.Action("GetDataSourceProducts", "Home")))
                  .Schema(schema => schema.Data("Data").Total("Total"))
              )
              .Filter(FilterType.Contains)
              .Value(Model.InitialProducts)
              )
    </div>

    <div>
        <button id="Save" type="submit">Save</button>
    </div>
}

 

Is there any kind of work around for this?

[Georgi Krustev]

Hello Sebastien Veilleux,

When same view is returned, the MVC wrapper will retrieve the values from the ModelState, because it needs to display the erroneous form state. In this case, the Value of the widget will not be equal to the Model.InitialProducts, but equal to the posted ProductIds. 

This is an expected behavior, and the only workaround is to remove the values from the ModelState (as it is shown in the aforementioned forum thread).

Regards,
Georgi Krustev
Telerik

[Sebastien Veilleux]

Thanks it is good to know.

I use ModelState.Remove("ProductIds") and it works now as I expected.