The value of the textbox doesn't change with ViewBag

Question

I wrote a short program but I'm not getting the expected result. Consider this view which simply is a form with two textboxes and a submit button:

@{ ViewBag.Title = "Index"; }
@using (Html.BeginForm("Index", "Home", FormMethod.Post))
{
    @Html.TextBox("Box1", (string)ViewBag.TextBox1)
    @Html.TextBox("Box2", (string)ViewBag.TextBox2)
    <input type="submit" value="Search" />
}

Here's my controller:

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

[HttpPost]
public ActionResult Index(string Box1, string Box2)
{
    ViewBag.TextBox1 = Box2;
    ViewBag.TextBox2 = Box1;
    return View("index",ViewBag);
}

Basically, I'm trying to switch the content of textbox1 and textbox2 when someone clicks the submit button. But no matter what I try it's not working (ie the values stay where they are). At first I thought may be the ?? has something to do with it but I commented out the lines with ?? but still got the same result. The instead of just doing return view() I tried return view("index", ViewBag) but that didn't make any difference. Anyone know what am I doing wrong here?

Its because the vales of `Box1` and `Box2` have been added to `ModelState` in your POST method, and the html helpers use the values from `ModelState` when they exist (refer [this answer](http://stackoverflow.com/questions/26654862/textboxfor-displaying-initial-value-not-the-value-updated-from-code/26664111#26664111) for an explanation. The correct approach is to follow the PRG pattern — , Sep 11 '15 at 22:07
@StephenMuecke Thank you. I was totally on wrong path on that one. — Zuzlx, Sep 11 '15 at 23:23

score 3 · Accepted Answer · answered Sep 11 '15 at 23:28

3

Just clear your model state and it will work. Replace your POST method with this code:

[HttpPost]
public ActionResult Index(string Box1, string Box2)
{
    ModelState.Clear();
    ViewBag.TextBox1 = Box2;
    ViewBag.TextBox2 = Box1;
    return View();
}

answered Sep 11 '15 at 23:28

Hernan Guzman

1,235
8
14

@herman guzman Thank you. Accepted answer. My own answer brought fear and tears into my heart. I knew it had to be a better way. – Zuzlx Sep 12 '15 at 14:13

score -2 · Answer 2 · answered Sep 11 '15 at 23:24

Here's what needs to be done on the controller. Talking about wordy for such a simple task:

    [HttpPost]
    public ActionResult Index(string Box1, string Box2)
    {

        ModelState.SetModelValue("Box1", new ValueProviderResult(Box2, string.Empty, System.Globalization.CultureInfo.InvariantCulture));
        ModelState.SetModelValue("Box2", new ValueProviderResult(Box1, string.Empty, System.Globalization.CultureInfo.InvariantCulture));


        return View();
    }

The value of the textbox doesn't change with ViewBag

2 Answers2