Asp.net MVC ModelState.Clear
asp.net-mvc, modelstate, post-redirect-get
Solution
I think is a bug in MVC. I struggled with this issue for hours today.
Given this:
public ViewResult SomeAction(SomeModel model)
{
model.SomeString = "some value";
return View(model);
}
The view renders with the original model, ignoring the changes. So I thought, maybe it does not like me using the same model, so I tried like this:
public ViewResult SomeAction(SomeModel model)
{
var newModel = new SomeModel { SomeString = "some value" };
return View(newModel);
}
And still the view renders with the original model. What's odd is, when I put a breakpoint in the view and examine the model, it has the changed value. But the response stream has the old values.
Eventually I discovered the same work around that you did:
public ViewResult SomeAction(SomeModel model)
{
var newModel = new SomeModel { SomeString = "some value" };
ModelState.Clear();
return View(newModel);
}
Works as expected.
I don't think this is a "feature," is it?
Problem
Can anyone give me a succinct definition of the role of ModelState in Asp.net MVC (or a link to one). In particular I need to know in what situations it is necessary or desirable to call `ModelState.Clear()`. Bit open ended huh... sorry, I think it might help if tell you what I'm acutally doing: I have an Action of Edit on a Controller called "Page". When I first see the form to change the Page's details everything loads up fine (binding to a "MyCmsPage" object). Then I click a button that generates a value for one of the MyCmsPage object's fields (`MyCmsPage.SeoTitle`). It generates fine and updates the object and I then return the action result with the newly modified page object and expect the relevant textbox (rendered using `<%= Html.TextBox("seoTitle", page.SeoTitle)%>`) to be updated ... but alas it displays the value from the old model that was loaded. I've worked around it by using `ModelState.Clear()` but I need to know why / how it has worked so I'm not just doing it blindly. PageController: ``` [AcceptVerbs("POST")] public ActionResult Edit(MyCmsPage page, string submitButton) { // add the seoTitle to the current page object page.GenerateSeoTitle(); // why must I do this? ModelState.Clear(); // return the modified page object return View(page); } ``` Aspx: ``` <%@ Page Language="C#" MasterPageFile="~/Views/Shared/Site.Master" Inherits="System.Web.Mvc.ViewPage<MyCmsPage>" %> .... <div class="c"> <label for="seoTitle"> Seo Title</label> <%= Html.TextBox("seoTitle", page.SeoTitle)%> <input type="submit" value="Generate Seo Title" name="submitButton" /> </div> ```