ASP.net MVC route parameter exception

Question

I have and action which takes a userId parameter:

~/Users/Show?userId=1234

Everything works fine except when the userId provided is not an int or is missing.

Then it throws this exception:

            Message: The parameters dictionary contains a null entry for parameter 'userId' of 
    non-nullable type 'System.Int32' for method 'System.Web.Mvc.ActionResult Show(Int32, 
System.Nullable`1[System.Boolean], System.String)' in 'S4U.Web.Mvc.Controllers.ProfileController'. An optional parameter must be a reference type, 
    a nullable type, or be declared as an optional parameter.
        Parameter name: parameters

..after which the user is redirected to the error page.

How do I configure the route so the action isn't hit at all and it throws a 404 instead?

Michal B. · Accepted Answer · 2012-03-02 11:53:34Z

4

Don't use a string as suggested somewhere below. Use:

public ActionResult (int userId = 0)
{

}

That's the best practise.

You can also do:

public ActionResult (int? userId)
{
    if (userId.HasValue)
    {
        //...
    }
}

answered Mar 2, 2012 at 11:53

Michal B.

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Rob West · Accepted Answer · 2012-03-02 11:55:04Z

1

As mentioned in my comment on Ufuk Hacıoğulları's answer you should handle validation either through adding a constraint to a route, through having a nullable type if the parameter can be empty.

For the former approach if you have an appropriate constraint this means your route will not be picked up - you will need a catch all route or other error handling. For the nullable type you can test in the action whether it has a value and act accordingly.

Keeping action paramters as strong types is a pattern to aim for.

answered Mar 2, 2012 at 11:55

Rob West

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