Pass a Dictionary<string,string> parameter in web api

Question

I'm trying to pass a Dictionary<string,string> object as a parameter to my web api method but if I inspect the log file it always comes through with a count of 0:

Web api method:

[HttpPost]
[ActionName("SendPost")]
public void SendPost([FromBody] Dictionary<string,string> values)
{
    using (var sw = new StreamWriter("F:\\PostTest.txt", true))
    {
        sw.WriteLine("Number of items in the dictionary - " + values.Count);
    }
}

Logic which calls the web api:

public HttpResponseMessage Send(string uri, string value)
{
    HttpResponseMessage responseMessage = null;

    using (var client = new HttpClient())
    {
        client.BaseAddress = new Uri(URI);
        client.DefaultRequestHeaders.Accept.Clear();
        client.DefaultRequestHeaders.Accept.Add(new MediaTypeWithQualityHeaderValue("application/json"));

        var content = new FormUrlEncodedContent
            (
                new Dictionary<string, string> { { "value", value } }
            );

        responseMessage = client.PostAsync(uri, content).Result;
    }
    return responseMessage;
}

Yuval Itzchakov · Accepted Answer · 2015-09-17 09:52:20Z

8

The problem is with the fact that you're saying the content-type is "application/json", yet you pass it as FormUrlEncodedContent. You need to either use StringContent and serialize the content to JSON yourself, or you can use the extention method HttpClientExtensions.PostAsJsonAsync which serializes the content to JSON for you:

public async Task<HttpResponseMessage> SendAsync(string uri, string value)
{
    using (var client = new HttpClient())
    {
        client.BaseAddress = new Uri(URI);
        client.DefaultRequestHeaders.Accept.Clear();
        client.DefaultRequestHeaders.Accept.Add(
                        new MediaTypeWithQualityHeaderValue("application/json"));

        return await client.PostAsJsonAsync(uri, content);
    }
}

answered Sep 17, 2015 at 9:52

Yuval Itzchakov

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4 Comments

Denys Wessels Over a year ago

I've changed my method to use PostAsJsonAsync but it's still saying the dictionary count in the log file is 0.Should I also change how I'm passing through the content in my example?

Yuval Itzchakov Over a year ago

@DenisWessels Did you use the code I posted? Or did you modify yours?

Denys Wessels Over a year ago

Sorry I'm being silly, I read your explanation properly and changed my logic to use PostAsJsonAsync and pass through the dictionary directly without creating FormUrlEncodedContent.Now it's working!

Yuval Itzchakov Over a year ago

@DenisWessels Great :)

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