Model not binding after posting in MVC?

Question

I am trying to sum two number using a from submit. HttpGet is working properly but on submit of the form I am unable to show it in view ..

public class CalculatorController : Controller
    {
        //
        // GET: /Calculator/

        public ActionResult Index()
        {
            return View();
        }
        [HttpGet]
        public ActionResult Sum()
        {
            CalculatorModel model = new CalculatorModel();
            model.FirstOperand = 3;
            model.SecondOperand = 4;
            model.Result = model.FirstOperand + model.SecondOperand;
            //Return the result
            return View(model);
        }

        [HttpPost]
        public ActionResult Sum(CalculatorModel model)
        {
            model.Result = model.FirstOperand + model.SecondOperand;
            //Return the result
            return View(model);
        }

    }

---

@model HTMLHelpersDemo.Models.CalculatorModel
@{
    ViewBag.Title = "Sum";
}

<h2>Sum</h2>

@using (Html.BeginForm("Sum", "Calculator", FormMethod.Post))
{
    <table border="0" cellpadding="3" cellspacing="1" width="100%">
        <tr valign="top">
            <td>
                @Html.LabelFor(model => model.FirstOperand)
                @Html.TextBoxFor(model => model.FirstOperand)
            </td>
        </tr>
        <tr valign="top">
            <td>
                @Html.LabelFor(model => model.SecondOperand)
                @Html.TextBoxFor(model => model.SecondOperand)
            </td>
        </tr>
        <tr valign="top">
            <td>
                @Html.LabelFor(model => model.Result)
                @Html.TextBoxFor(model => model.Result)
            </td>
        </tr>
    </table>
    <div style="text-align:right;">
        <input type="submit" id="btnSum" value="Sum values" />
    </div>
}

Initially it's showing 7 as 3 plus 4

but when I changed my value and post it it's not showing the old value ..Have debugged in controller it's showing perfectly but not posting to view properly

Answer 1

You need to clear the previous result value from model state dictionary. You may use the ModelState.Clear() method to do that.

[HttpPost]
public ActionResult Sum(CalculatorModel model)
{
    ModelState.Clear();
    model.Result = model.FirstOperand + model.SecondOperand;         
    return View(model);
}