Asp.net-mvc – ASP.Net MVC Html.HiddenFor with wrong value

asp.net-mvcasp.net-mvc-3hidden-fieldshtml.hiddenfor

I'm using MVC 3 in my project, and I'm seeing a very strange behavior.

I'm trying to create a hidden field for a particular value on my Model, the problem is that for some reason the value set on the field does not correspond to the value in the Model.

e.g.

I have this code, just as a test:

<%:Html.Hidden("Step2", Model.Step) %>
<%:Html.HiddenFor(m => m.Step) %>

I would think that both hidden fields would have the same value.
What I do is, set the value to 1 the first time I display the View, and then after the submission I increase the value of the Model field by 1.

So, the first time I render the page both controls have the value 1, but the second time the values rendered are these:

<input id="Step2" name="Step2" type="hidden" value="2" />
<input id="Step" name="Step" type="hidden" value="1" />

As you can see, the first value is correct, but the second value seems to be the same as the first time I display the View.

What am I missing? Are the *For Html helpers caching the values in some way? If so, how can I disable this caching?.

Thanks for your help.

Best Answer

That's normal and it is how HTML helpers work. They first use the value of the POST request and after that the value in the model. This means that even if you modify the value of the model in your controller action if there is the same variable in the POST request your modification will be ignored and the POSTed value will be used.

One possible workaround is to remove this value from the model state in the controller action which is trying to modify the value:

// remove the Step variable from the model state 
// if you want the changes in the model to be
// taken into account
ModelState.Remove("Step");
model.Step = 2;

Another possibility is to write a custom HTML helper which will always use the value of the model and ignore POST values.

And yet another possibility:

<input type="hidden" name="Step" value="<%: Model.Step %>" />

Related Solutions

Asp.net-mvc – A potentially dangerous Request.Form value was detected from the client

I think you are attacking it from the wrong angle by trying to encode all posted data.

Note that a "<" could also come from other outside sources, like a database field, a configuration, a file, a feed and so on.

Furthermore, "<" is not inherently dangerous. It's only dangerous in a specific context: when writing strings that haven't been encoded to HTML output (because of XSS).

In other contexts different sub-strings are dangerous, for example, if you write an user-provided URL into a link, the sub-string "javascript:" may be dangerous. The single quote character on the other hand is dangerous when interpolating strings in SQL queries, but perfectly safe if it is a part of a name submitted from a form or read from a database field.

The bottom line is: you can't filter random input for dangerous characters, because any character may be dangerous under the right circumstances. You should encode at the point where some specific characters may become dangerous because they cross into a different sub-language where they have special meaning. When you write a string to HTML, you should encode characters that have special meaning in HTML, using Server.HtmlEncode. If you pass a string to a dynamic SQL statement, you should encode different characters (or better, let the framework do it for you by using prepared statements or the like)..

When you are sure you HTML-encode everywhere you pass strings to HTML, then set ValidateRequest="false" in the <%@ Page ... %> directive in your .aspx file(s).

In .NET 4 you may need to do a little more. Sometimes it's necessary to also add <httpRuntime requestValidationMode="2.0" /> to web.config (reference).

Asp.net-mvc – Compile Views in ASP.NET MVC

From the readme word doc for RC1 (not indexed by google)

ASP.NET Compiler Post-Build Step

Currently, errors within a view file are not detected until run time. To let you detect these errors at compile time, ASP.NET MVC projects now include an MvcBuildViews property, which is disabled by default. To enable this property, open the project file and set the MvcBuildViews property to true, as shown in the following example:

<Project ToolsVersion="3.5" DefaultTargets="Build" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
  <PropertyGroup>
    <MvcBuildViews>true</MvcBuildViews>
  </PropertyGroup>

Note Enabling this feature adds some overhead to the build time.

You can update projects that were created with previous releases of MVC to include build-time validation of views by performing the following steps:

Open the project file in a text editor.
Add the following element under the top-most <PropertyGroup> element: <MvcBuildViews>true</MvcBuildViews>
At the end of the project file, uncomment the <Target Name="AfterBuild"> element and modify it to match the following:

<Target Name="AfterBuild" Condition="'$(MvcBuildViews)'=='true'">
    <AspNetCompiler VirtualPath="temp" PhysicalPath="$(ProjectDir)\..\$(ProjectName)" />
</Target>

Best Answer

Related Solutions

Asp.net-mvc – A potentially dangerous Request.Form value was detected from the client

Asp.net-mvc – Compile Views in ASP.NET MVC

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