Web API post data: object reference not set to an instance of an object

Question

I am trying to get Web API working with POST and I have the following in my Controller: ``` public class mainGridController : ApiController { public class formData { public string module { get; set; } public string group { get; set; } public string staff { get; set; } } public HttpResponseMessage Post([FromBody] formData data) { string string_group = ""; string string_staff = ""; if (data.group != null) { ``` But I seem to be getting "object reference is not set to an instance of an object" for data.group in my "if" statement. Here is my route info: ``` protected void Application_Start(object sender, EventArgs e) { GlobalConfiguration.Configuration.Routes.MapHttpRoute( name: "DefaultApi", routeTemplate: "api/{controller}/{data}", defaults: new { module = System.Web.Http.RouteParameter.Optional, data = System.Web.Http.RouteParameter.Optional} ); } ``` Does anyone know what could be causing this? I am trying to post using jQuery. Here is my jQuery code: ``` var url = "api/mainGrid"; var…

Accepted Answer

The problem is you have specified the `dataType` parameter as `json` but you are passing a JS object - which of course isn't JSON.

You need to convert your `data` object to actual JSON for this to work

```
data: JSON.stringify({
    group: JSON.stringify(checkedGroups),
    staff: JSON.stringify(checkedStaff),
    module: JSON.stringify(selectedModuleSEQ)
}),
```

Web API post data: object reference not set to an instance of an object

Solution

Problem