Christopher Kellner Christopher Kellner - 2 months ago 20
ASP.NET (C#) Question

ASP MVC 5 controller parameter does not become null

I ran into the following problem:

I've got a asp.net mvc 5 controller with a reference type as a parameter:

[Route("")]
[HttpGet]
public ActionResult GetFeeds(Location location)
{
if (location == null)
{
// init location or smth
}

// Do smth with location

return new EmptyResult();
}


You will notice that I'm using AttributeRouting. There are NO other methods with the name of this action.

However - this is my location class:

public class Location : ILocation
{
public DbGeography Coordinates { get; set; }

public double Latitude { get; set; }

public double Longitude { get; set; }
}


Nothing special here (the interface defines all of those properties).

If I'm accessing the controllers action (actually using powershell) and passing something like:

http://localhost:2000/Feed?latitude=23.1&longitude=37


everthing works fine but if I'm using

http://localhost:2000/Feed


the location parameter is NOT null (it is a new Location with default values), which is the behavior I want to have :( .

Does anyone have an idea why this happens?

Thanks in advance

Answer

The MVC model binder has taken over. What I originally posted would work in instances that do not go through the model binder. However, based on other answers on SO and my own quick testing, it appears that a viewmodel parameter will never be null due to how the binder works and ties properties to form values.

In your instance, I would check if both latitude and longitude are null to see if nothing was passsed. Which means you will need to make them nullable on your ViewModel

public class Location : ILocation
    {
       public DbGeography Coordinates { get; set; }

       public double? Latitude { get; set; }

       public double? Longitude { get; set; }
    }

Updated Controller Code

if (location.Latitude == null && location.Longitude == null)
    {
        // init location or smth
    }
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