How to use ViewModels in ASP.NET MVC?

Question

I just started learning about ViewModels in ASP.NET MVC. So, I thought of implementing a sample example as below:

Business Entity

public class AddModel
{
    public int a { get; set; }
    public int b { get; set; }

    public int Add()
    {
        return (this.a + this.b);
    }
}

Add ViewModel

public class AddViewModel
{
    public AddModel addModel;
    public int Total { get; set; }
}

Controller

public class AddController : Controller
{
    [HttpPost]
    public JsonResult Add(AddViewModel model)
    {

        int iSum = model.addModel.a + model.addModel.b;
        model.Total = iSum;
        return Json(model);

    }

    public ActionResult Index()
    {
        return View();
    }
}

View Implementation

@model ViewModelApplication.AddViewModel
<script type="text/javascript" src="../../Scripts/MicrosoftAjax.js"></script>
<script src="../../Scripts/MicrosoftMvcAjax.debug.js" type="text/javascript"></script>
<script type="text/javascript">
    function Callback(data) {
        alert("I am sucess call");
    }

    function Failed() {
        alert("I am a failure call");
    }
</script>

@using (Ajax.BeginForm("Add", "Add", new AjaxOptions { OnSuccess = "Callback", OnFailure = "Failed" }))
{
    <table align="center">
        <tr>
            <td class="tdCol1Align">
                <label>
                    Number1</label>
            </td>
            <td class="tdCol2Align">
                @Html.TextBoxFor(Model => Model.addModel.a)
            </td>
        </tr>
        <tr>
            <td class="tdCol1Align">
                <label>
                    Number2</label>
            </td>
            <td class="tdCol2Align">
                @Html.TextBoxFor(Model => Model.addModel.b)
            </td>
        </tr>
        <tr>
            <td colspan="2" align="center">
                <input type="submit" value="Add" class="button" />
            </td>
        </tr>
    </table>
}

The problem here is that I am unable to retrieve the values entered into the text boxes whenever the Add button is clicked; the corresponding AJAX action is being it.

When I try to access the values of a and b, I get nulls instead of the values entered into the text boxes.

I am not sure where I am going wrong. Please help.

Answer 1

your view model should look like this

public class AddViewModel
    {
        public int a { get; set; }
        public int b { get; set; }
        public int Total { get; set; }
    }

and in the cshtml

            <td class="tdCol2Align">
                @Html.TextBoxFor(m=> m.a)
            </td>

            <td class="tdCol2Align">
                @Html.TextBoxFor(m=> m.b)
            </td>

in the controller

        [HttpPost]
        public JsonResult Add(AddViewModel model)
        {
            int iSum = model.a + model.b;
            model.Total = iSum;
            return Json(model);

        }

Edit

View model is there to render your views don't place any logic inside that. if you have more complex model then it will be hard to map Model with ViewModel. for this you can use AutoMapper or ValueInjector for mapping between model and view model.

link for automapper http://automapper.codeplex.com/

link for value injector http://valueinjecter.codeplex.com/

hope this helps