How to get POST data in WebAPI?

After spending a good bit of time today trying to wrap my brain around the (significant but powerful) paradigm shift between old ways of processing web form data and how it is done with WebAPI, I thought I'd add my 2 cents to this discussion.

What I wanted to do (which is pretty common for web form processing of a POST) is to be able to grab any of the form values I want, in any order. Say like you can do if you have your data in a System.Collections.Specialized.NameValueCollection. But turns out, in WebAPI, the data from a POST comes back at you as a stream. So you can't directly do that.

But there is a cool little class named FormDataCollection (in System.Net.Http.Formatting) and what it will let you do is iterate through your collection once.

So I wrote a simple utility method that will run through the FormDataCollection once and stick all the values into a NameValueCollection. Once this is done, you can jump all around the data to your hearts content.

So in my ApiController derived class, I have a post method like this:

    public void Post(FormDataCollection formData)
    {
        NameValueCollection valueMap = WebAPIUtils.Convert(formData);

        ... my code that uses the data in the NameValueCollection
    }

The Convert method in my static WebAPIUtils class looks like this:

    /// <summary>
    /// Copy the values contained in the given FormDataCollection into 
    /// a NameValueCollection instance.
    /// </summary>
    /// <param name="formDataCollection">The FormDataCollection instance. (required, but can be empty)</param>
    /// <returns>The NameValueCollection. Never returned null, but may be empty.</returns>
    public static NameValueCollection Convert(FormDataCollection formDataCollection)
    {
        Validate.IsNotNull("formDataCollection", formDataCollection);

        IEnumerator<KeyValuePair<string, string>> pairs = formDataCollection.GetEnumerator();

        NameValueCollection collection = new NameValueCollection();

        while (pairs.MoveNext())
        {
            KeyValuePair<string, string> pair = pairs.Current;

            collection.Add(pair.Key, pair.Value);
        }

        return collection;
     }

Hope this helps!

I had a problem with sending a request with multiple parameters.

I've solved it by sending a class, with the old parameters as properties.

<form action="http://localhost:12345/api/controller/method" method="post">
    <input type="hidden" name="name1" value="value1" />
    <input type="hidden" name="name2" value="value2" />
    <input type="submit" name="submit" value="Submit" />
</form>

Model class:

public class Model {
    public string Name1 { get; set; }
    public string Name2 { get; set; }
}

Controller:

public void method(Model m) {
    string name = m.Name1;
}

It is hard to handle multiple parameters on the action directly. The better way to do it is to create a view model class. Then you have a single parameter but the parameter contains multiple data properties.

public class MyParameters
{
    public string a { get; set; } 
    public string b { get; set; }
}

public MyController : ApiController
{
    public HttpResponseMessage Get([FromUri] MyParameters parameters) { ... }
}

Then you go to:

http://localhost:12345/api/MyController?a=par1&b=par2

Reference: http://www.asp.net/web-api/overview/formats-and-model-binding/parameter-binding-in-aspnet-web-api

If you want to use "/par1/par2", you can register an asp routing rule. eg routeTemplate: "API/{controller}/{action}/{a}/{b}".

See http://www.asp.net/web-api/overview/web-api-routing-and-actions/routing-in-aspnet-web-api

Try this.

public string Post(FormDataCollection form) {
    string par1 = form.Get("par1");

    // ...
}

It works for me with webapi 2

I found for my use case this was much more useful, hopefully it helps someone else that spent time on this answer applying it

public IDictionary<string, object> GetBodyPropsList()
        {
            var contentType = Request.Content.Headers.ContentType.MediaType;
            var requestParams = Request.Content.ReadAsStringAsync().Result;

            if (contentType == "application/json")
            {
                return Newtonsoft.Json.JsonConvert.DeserializeObject<IDictionary<string, object>>(requestParams);
            }
            throw new HttpResponseException(HttpStatusCode.UnsupportedMediaType);
        }

None of the answers here worked for me. Using FormDataCollection in the post method seems like the right answer but something about my post request was causing webapi to choke. eventually I made it work by including no parameters in the method call and just manually parsing out the form parameters like this.

public HttpResponseMessage FileUpload() {
    System.Web.HttpRequest httpRequest = System.Web.HttpContext.Current.Request;
    System.Collections.Specialized.NameValueCollection formData = httpRequest.Form;
    int ID = Convert.ToInt32(formData["ID"]);
    etc

Is there a way to handle form post data in a Web Api controller?

The normal approach in ASP.NET Web API is to represent the form as a model so the media type formatter deserializes it. Alternative is to define the actions's parameter as NameValueCollection:

public void Post(NameValueCollection formData)
{
  var value = formData["key"];
}

    ON WEB API.


    [HttpGet]
    [Route("api/Get_EXCUTA_PROCEDURE_IBESVNDACMVDD")]
    public IHttpActionResult Get(int CodigoPuxada...)
    {
        string retornoErro = string.Empty;
        try
        {
            //int codigoPuxada = entrada.CodigoPuxada;

            SetKeyAtual(CodigoPuxada);

            var repo = new ItemBroker_Dim_Canal_BookRepositorio(ConnectionString);

            try
            {
                var dadosRetorno = repo.ExcuteProcedure_Busca_vbc_(CodigoPuxada,...); //  method return object  (dataset)
                return Ok(dadosRetorno);
            }
            catch
            {
                throw;
            }
        }
        catch (Exception ex)
        {
            retornoErro = ex.Message;
            if (ex.InnerException != null)
                retornoErro = ex.InnerException.ToString();
        }

        return Ok(retornoErro); 
    }


    Other projet invoke web api...
    (USING RESTSHARP DLL)

    RestClient clientHttpPost1 = null;
    string dadosVbc123 = string.empty;
                
    clientHttpPost1 = new RestSharp.RestClient($"{urlWebApiAvante}Get_EXCUTA_PROCEDURE_IBESVNDACMVDD?CodigoPuxada=...");

    RestSharp.RestRequest request2 = new RestSharp.RestRequest(RestSharp.Method.GET);
    request2.RequestFormat = RestSharp.DataFormat.Json;
    request2.AddHeader("Content-Type", "application/json;charset=utf-8");
    string strAux1 = string.Empty;
    request2.Timeout = 180000;
    RestSharp.IRestResponse response = clientHttpPost1.Execute(request2);
    if ((response != null) && response.StatusCode == System.Net.HttpStatusCode.OK)
    {
        try
        {
            var dataObjects = response.Content.ToString().Trim();
            dadosVbc123 = dataObjects.ToString().Replace("\t", "");
            if (dadosVbc123.Trim() == "{\"IBESVNDACMVDD\":[]}")
            dadosVbc123 = string.Empty;
        }
        ...
    }

    //  converting  JSON to dataset
    string val1 = dadosVbc123.Replace("{\"IBESVNDACMVDD\":", "").Replace("}]}", "}]");
    DataTable dtVBC123 = (DataTable)Newtonsoft.Json.JsonConvert.DeserializeObject(val1, (typeof(DataTable)));