How do I use Optional Parameters in an ASP.NET MVC Controller

Solution 1:

The string should be ok, as it'll get passed as an empty string. For int, make it nullable:

public ActionResult Index(string Country, int? Regions)

Also, you'll note I capitalized it in the same was as your querystring.

Edit

Note that ASP.NET now allows you to define default parameters. E.g.:

public ActionResult Index(string Country, int Regions = 2)

However, IMHO I'd recommend that you only use the default where it makes semantic sense. For example, if the purpose of the Regions parameter were to set the # of regions in a country, and most countries have 2 regions (North and South) then setting a default makes sense. I wouldn't use a "magic number" that signifies a lack of input (e.g., 999 or -1) -- at that point you should just use null.

Solution 2:

I know this is quite old, but for posterity it's important to note that as of C# 2010 (aka 4.0, released with .NET 4) you could use an optional argument if you wanted to avoid the potential pitfalls that come with nullable types. Your method signature would look like this:

public ActionResult Index(string Country, int Regions = -1)