Question

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.

Answer 1

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 %>" />