Asp.Net MVC view does not display model changes made by controller

Question

I am new to ASP.NET MVC and need some help.
When the action "P01" is triggered by post, I get a strongly typed model as a parameter, change the properties of the instance of this model and call "return View (model)".
The im view uses the syntax "@ Html.TextBoxFor (m => m.p01campo01)". Someone here had a similar problem and got advice on using im using syntax.
Someone here uses the syntax "<% = Html.TextBox (" Person.LastName ", ViewData.Model.LastName) → The problem is that when rendering a view, the text field has the last published value, and not the value assigned in the controller .

Thanks to everyone who tried to help me here, I will answer the first answer that works.

There is my code:

*************************************************
using System;
using System.Collections.Generic;
using System.ComponentModel.DataAnnotations;
using System.Globalization;
using System.Linq;
using System.Web;
using System.Web.Mvc;
using System.Web.Security;

namespace MyTest.Models
{
    //-------
    public class testePg01
    {        
        [DataType(DataType.Text)]
        [Display(Name = "p01campo01")]
        public string p01campo01 { get; set; }

        [DataType(DataType.Text)]
        [Display(Name = "p01campo02")]
        public string p01campo02 { get; set; }

    }
    //-------
}
*************************************************

*************************************************
using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.Mvc;
using MyTest.Models;

namespace MyTest.Controllers
{
    public class TesteController : Controller
    {
        //-------
        [AcceptVerbs(HttpVerbs.Get)]        
        public ActionResult P01()
        {
            return View();
        }
        //-------
        [AcceptVerbs(HttpVerbs.Post)]
        [ValidateAntiForgeryToken]
        public ActionResult P01(testePg01 model)
        {
            model.p01campo01 = model.p01campo01 + "#updatedHereButNotInView";
            model.p01campo02 = model.p01campo02 + "#updatedHereButNotInView";
            return View(model); // it dont return updated
        }
        //-------

    }
}
*************************************************

*************************************************
@model MyTest.Models.testePg01

@{
    ViewBag.Title = "P01";
}

<h2>P01</h2>

<script src="@Url.Content("~/Scripts/jquery.validate.min.js")" type="text/javascript"></script>
<script src="@Url.Content("~/Scripts/jquery.validate.unobtrusive.min.js")" type="text/javascript"></script>

@Html.ValidationSummary(true, "Erro na pagina.")

@using (Html.BeginForm()) {
    @Html.AntiForgeryToken()
    <div>    
        <fieldset>
            <legend>Test P01</legend>

            <div class="editor-label">
                @Html.LabelFor(m => m.p01campo01)
            </div>
            <div class="editor-field">
                @Html.TextBoxFor(m => m.p01campo01)
                @Html.ValidationMessageFor(m => m.p01campo01)
            </div>

            <div class="editor-label">
                @Html.LabelFor(m => m.p01campo02)
            </div>
            <div class="editor-field">
                @Html.TextBoxFor(m => m.p01campo02)
                @Html.ValidationMessageFor(m => m.p01campo02)
            </div>
            <p>
                <input type="submit" value="P01" />
            </p>
        </fieldset>
    </div>
}
*************************************************

Answer 1

Since HttpPost HTML helpers are first looking for POSTED data and only then to the model.

You must remove the property from the state:

[AcceptVerbs(HttpVerbs.Post)]
[ValidateAntiForgeryToken]
public ActionResult P01(testePg01 model)
{
    ModelState.Remove("p01campo01");
    ModelState.Remove("p01campo02");

    model.p01campo01 = model.p01campo01 + "#updatedHereButNotInView";
    model.p01campo02 = model.p01campo02 + "#updatedHereButNotInView";

    return View(model);         
}

Since ModelState is a dictionary, you can also use Clear()to remove all properties from a state:

ModelState.Clear();

By the way, you can use MVC3 [HttpPost]and [HttpGet]insted[Acceptverb(...)]

Answer 2

Model changes made in the message are not displayed by default. Instead, it uses what was passed in the model to the controller method. To fix this, try adding:

ModelState.Clear();

immediately before RedirectToAction.

Answer 3

This is a very ugly workaround you can try

 public class TesteController : Controller
    {
        //-------
        [AcceptVerbs(HttpVerbs.Get)]        
        public ActionResult P01(string val1,string val2)
        {
            var model = new testePg01();
            if(!(String.IsEmptyOrNull(val1)&&String.IsEmptyOrNull(val2)))
                  { 
                       model.p01campo01  = val1;
                       model.p01campo02 = val2;

                  }
            return View(model);
        }
        //-------
        [AcceptVerbs(HttpVerbs.Post)]
        [ValidateAntiForgeryToken]
        public ActionResult P01(testePg01 model)
        {
            model.p01campo01 = model.p01campo01 + "#updatedHereButNotInView";
            model.p01campo02 = model.p01campo02 + "#updatedHereButNotInView";
            return RedirectToAction("P01",{val1=model.p01campo01,val2=model.p01campo02})          
        }
   }

Answer 4

Ignore the PRG sentence below. This is ugly. Use instead:

public ActionResult P01(TestePg01 model)
    {
        model.P01campo01 = model.P01campo01 + "#updatedHereButNotInView";
        model.P01campo02 = model.P01campo02 + "#updatedHereButNotInView";
        ModelState.Clear(); //this will re-populate the view

        return View(model);
    }

Use the post-redirect-get pattern:

    public class TesteController : Controller
{
    //-------
    [AcceptVerbs(HttpVerbs.Get)]
    public ViewResult P01(TestePg01 o)
    {
        return base.View(o);
    }
    //-------
    [AcceptVerbs(HttpVerbs.Post)]
    [ValidateAntiForgeryToken]
    public ActionResult P01Post(TestePg01 model)
    {
        model.P01campo01 = model.P01campo01 + "#updatedHereButNotInView";
        model.P01campo02 = model.P01campo02 + "#updatedHereButNotInView";
        return RedirectToAction("P01", model);
    }
    //-------
}

in view:

@using (Html.BeginForm("P01Post", "Teste")) {//...}