MVC ViewModel未在View中填充

Question

I am trying to take an input from a text box, replace some strings within it - and return both the original and the replacement strings to the View, and populate two separate text boxes.

My simple view model is:

public class WordsToConvert
{
    public string Original { get; set; }
    public string Replacement { get; set; }
}

My cshtml file has a form, which is the same form I would like populated when the Post returns to the same view:

            @Html.EditorFor(model => model.Original, 
                  new { htmlAttributes = new { @class = "form-control" } })

            @Html.EditorFor(model => model.Replacement, 
                  new { htmlAttributes = new { @class = "form-control" } })

My controller is very simple (just to get started):

    // POST: WTC
    [HttpPost]
    [ValidateAntiForgeryToken]
    public ActionResult WTC([Bind(Include = "Original,Replacement")] WordsToConvert wordsToConvert)
    {
        if (ModelState.IsValid)
        {
            wordsToConvert.Replacement = "Test " + wordsToConvert.Original;
            return View(wordsToConvert); // <---- at this point Watch shows wordsToConvert.Replacement as "Test whatever other text"
        }

        return View(wordsToConvert);
    }

I can see wordsToConvert.Replacement changing in the Watch window in VS - but when the View displays it again, it's blank.

If I add @Model.Replacement to the view - then I can see the updated "original" with "Test - xxxxx" at the front.

Is there anything I can do to get the Replacement text to show in the replacement textbox/EditorFor?

Thanks, Mark

Answer 1

This is a well known gotcha in MVC.

ModelState.Clear();

Will fix the issue. You can also do it individually if you want to target just one field:

ModelState.Remove("Replacement");

The reason is complicated, and has to do with a choice the MVC team made to try and do the right thing most of the time for people (but sometimes this is the wrong thing for some people).

http://blogs.msdn.com/b/simonince/archive/2010/05/05/asp-net-mvc-s-html-helpers-render-the-wrong-value.aspx