//uri of asp.net web api
readonly string uri = "http://192.168.1.101//WebApiDemo/api/Values";

//This Function call in Android on button click event
public async Task<String> GetCarsAsync()
{
    using (HttpClient httpClient = new HttpClient())
    {
        var response = await httpClient.GetStringAsync(uri);
        return JsonConvert.DeserializeObject<String>(response);
    }
}