How do I accept an array as an ASP.NET MVC controller action parameter?

Question

I have an ASP.net MVC controller called Designs that has an action with the following signature:

public ActionResult Multiple(int[] ids) 

However, when I try to navigate to this action using the url:

http://localhost:54119/Designs/Multiple?ids=24041,24117 

The ids parameter is always null. Is there any way to get MVC to convert the ?ids= URL query parameter into an array for the action? I've seen talk of using an action filter but as far as I can tell that will only work for POSTs where the array is passed in the request data rather than in the URL itself.

Answer 1

The default model binder expects this url:

http://localhost:54119/Designs/Multiple?ids=24041&ids=24117 

in order to successfully bind to:

public ActionResult Multiple(int[] ids) {     ... } 

And if you want this to work with comma separated values you could write a custom model binder:

public class IntArrayModelBinder : DefaultModelBinder {     public override object BindModel(ControllerContext controllerContext, ModelBindingContext bindingContext)     {         var value = bindingContext.ValueProvider.GetValue(bindingContext.ModelName);         if (value == null || string.IsNullOrEmpty(value.AttemptedValue))         {             return null;         }          return value             .AttemptedValue             .Split(',')             .Select(int.Parse)             .ToArray();     } } 

and then you could apply this model binder to a particular action argument:

public ActionResult Multiple([ModelBinder(typeof(IntArrayModelBinder))] int[] ids) {     ... } 

or apply it globally to all integer array parameters in your Application_Start in Global.asax:

ModelBinders.Binders.Add(typeof(int[]), new IntArrayModelBinder()); 

and now your controller action might look like this:

public ActionResult Multiple(int[] ids) {     ... } 

Answer 2

To extend on Darin Dimitrov's answer, something you can get away with is accepting a simple string in your URL parameter and converting it to an array yourself:

public ActionResult Multiple(string ids){   int[] idsArray = ids.Split(',').Select(int.Parse).ToArray();   /* ...process results... */ } 

If you get a parse error while doing this (because someone passed you a malformed array), you can cause your exception handler to return a 400 Bad Request error instead of the default, more unfriendly 404 Not Found error that MVC returns when an endpoint is not found.