Webmatrix: passing ModelState to partial page

Question

I am building a WebPages site and have an issue when I try to pass ModelState data to a partial page.

Here is the code for Create.cshtml:

@{
    Page.Title = "Create Fund";

    var name = "";

    if (IsPost) {
        name = Request.Form["name"];

        if (!name.IsValidStringLength(2, 128)) {
            ModelState.AddError("name", "Name must be between 2 and 128 characters long.");
        }
    }
}

@RenderPage("_fundForm.cshtml", name)

Here is the code for _fundForm.cshtml:

@{
    string name = PageData[0];
}

<form method="post" action="" id="subForm">
    <fieldset>
        @Html.ValidationSummary(true)
        <legend>Fund</legend>
        <p>
            @Html.Label("Name:", "name")
            @Html.TextBox("name", name)
            @Html.ValidationMessage("name", new { @class = "validation-error" })
        </p>
        <p>
            <input type="submit" name="submit" value="Save" />
        </p>
    </fieldset>
</form>

The issue I am having is when there is an error for "name", the validation error does not display. Is there a special way to pass ModelState between the two pages?

_fundForm is going to be shared between Create.cshtml and Edit.cshtml.

Answer 1

ModelState is a readonly property of System.Web.WebPages.WebPage class. Its backing field is a private ModelStateDictionary and is initialized at first access. I can't see any way to force ModelState across pages, apart from doing it via reflection as seen in SO question: Can I change a private readonly field in C# using reflection?

Otherwise, you can simply use a third parameter in the invocation, like this:

@RenderPage("_fundForm.cshtml", name, ModelState);

In effect, the first parameter after the page name will become the Model of the new page, so there is enough space (i.e. the next parameter) to pass the ModelState.

In your "_fundForm.cshtml" merge the ModelState received by the calling page with the local one, like this:

@{
    //In _fundForm.cshtml
    var ms = PageData[1];
    ModelState.Merge((ModelStateDictionary)ms);
}