Using HttpClient for Rest service

MatteoPolito · October 2013

Hi guys,

I have to consume a Rest Service, created using Asp.Net Web API (but this is not important), on a project with Xamarin iOS.
I know that I can use ServiceStack or RestSharp but I want to try to use HttpClient.

To deserialise response I need to use method "ReadAsAsync" contained in "System.Net.Http.Formatting" but this It's not included in Framework. I've tried to use assembly contained in Mono 3.2.3 but I have this error:

Error CS1705: Assembly System.Net.Http.Formatting, Version=4.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35' referencesSystem.Net.Http, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a' which has a higher version number than imported assembly `System.Net.Http, Version=2.0.5.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a' (CS1705)

I want to ask to you how properly use HttpClient to consume Rest Service?

I want simply to execute this code on my Xamarin.iOS app:

HttpResponseMessage response = client.GetAsync("api/products").Result; // Blocking call!
if (response.IsSuccessStatusCode)
{
// Parse the response body. Blocking!
var products = response.Content.ReadAsAsync<IEnumerable>().Result;
foreach (var p in products)
{
Console.WriteLine("{0}\t{1};\t{2}", p.Name, p.Price, p.Category);
}
}
else
{
Console.WriteLine("{0} ({1})", (int)response.StatusCode, response.ReasonPhrase);
}

I hope you help me.

Thanks!!

DannyC · October 2013

@mapo80 not sure if you are returning XML or Json but would suggest returning JSON and parsing with Json.net. Check out the store component.

http://components.xamarin.com/view/json.net

MatteoPolito · October 2013

Yes, rest service returns JSON. Yes, now I'm using json.net with this code:

string path = "";
HttpResponseMessage response = Client.GetAsync(path).Result;
if (response.IsSuccessStatusCode)
{
var object = JsonConvert.DeserializeObject (response.Content.ReadAsStringAsync ().Result);

}

Is this right? So, it's not possible to use System.Net.Http.Formatting!

Thanks for your answer.

Spartan · December 2013

To use Formatting please install the PCL library Microsoft ASP.NET Web API 2 Client using Nuget.

MatteoPolito · December 2013

Great, thanks! I'll try it.

GrantCause · December 2013

@mapo80 here is what I would do:

`
Create a product item class file as follows:

public class ProductItem
{
    public ProductItem ()
    {
    }

    public string name { get; set; }
    public string price { get; set; }
    public string category { get; set; }
}

This task can be made easier by using http://json2csharp.com/ and giving it the JSON output from your call or the URL for the call.

Once you have this then use the following to make the HTTP request / response calls where SearchRequest is the URL Encoded http web address of your API. Note only URL encode the parameters to the request usually this is the stuff after &param= in quotes:

    private string UrlEncodeParameter(string paramToEncode)
    {
        string urlEncodedParam = string.Empty;

        // remove whitespace from search parameter and URL encode it
        urlEncodedParam = paramToEncode.Trim();
        urlEncodedParam = Uri.EscapeDataString(urlEncodedParam);

        return urlEncodedParam;
    }

    private HttpWebRequest SetHttpRequest(string apiCredentials, string SearchRequest)
    {
        _httpRequest = (HttpWebRequest)null;

        if (string.IsNullOrEmpty(SearchRequest))
            throw new ArgumentNullException(string.Format("A search request is required by the Search method"));

        // Attempt to establish http request
        try
        {
            _httpRequest = (HttpWebRequest)HttpWebRequest.Create(new Uri(SearchRequest));
            _httpRequest.Credentials = new NetworkCredential (apiCredentials, apiCredentials);
        } catch (Exception ex) {
            string message = string.Format("Error creating request.  Check inner details for more info: {0}", SearchRequest);
            var requestException = new ApplicationException(message, ex);
            throw requestException;
        }

        return _httpRequest;
    }


    public HttpWebResponse Search()
    {
        // Attempt to get http response
        HttpWebResponse response = (HttpWebResponse)null;
        try
        {
            response = (HttpWebResponse)apiSearchParameters.HttpRequest.GetResponse();
            if (response.StatusCode != HttpStatusCode.OK) {
                throw new Exception(String.Format("Server error (HTTP {0}: {1}).", response.StatusCode,
                    response.StatusDescription));
            }
            return response;
        }
        catch (Exception ex)
        {
            Console.WriteLine(ex.Message);
            return response;
        }
    }

Now using Newtonsoft.Json.Net deserialise the Product Item from the JSON response:

        // Create a basic search request
        HttpWebRequest httpWebRequest = SetHttpRequest("your api credentials", “your URL encoded http url for the API");
        Console.WriteLine("httpWebRequest = " + httpWebRequest.Address.AbsoluteUri);

        // Perform search
        try
        {
            HttpWebResponse httpRes = Search();
            if (httpRes != null)
            {
                var responseStream = httpRes.GetResponseStream();

                var json = (JsonObject)JsonObject.Load(responseStream);

                var deserializedJsonRecords = JsonConvert.DeserializeObject<ProductItem>(json.ToString());

               var searchResults = new List<ProductItem>();

               searchResults = (
                  from result in deserializedJsonRecords
                  select new ProductItem {
                      name = result.name,
                      price = result.price, 
                      category = result.category
                  }
               ).ToList();
            }
        } catch (Exception ex) {
            Console.WriteLine(ex.Message);
        }

Hope this helps.
`

MatteoPolito · December 2013

Ok, thanks for your answer.

SKall · December 2013

Don't use a blocking web call. Here is an example client which uses abstracted serializers (and supports Json.NET and ServiceStack plugins):

https://github.com/sami1971/SimplyMobile/blob/master/Core/SimplyMobile.Web/RestClient.cs

MatteoPolito · December 2013

Great thanks.

My goal is to create a project for my rest service that I can use in my MonoDroid and MonoTouch application.

I don't want to create a project for every application. I've seen that HttpClient is platform specific (http://forums.xamarin.com/discussion/7719/using-httpclient).

I've to use pcl version of HttpClient?

SKall · December 2013

HttpClient can be PCL if you don't want WP8 support. If you do, then either create an interface for the web client and then use DI at runtime. Using Microsoft's async HttpClient PCL library has been troublesome.

softlion · December 2013

HttpClient can be PCL if you don't want WP8 support

That is not true. I have http client set up in the same pcl project used by all 3 platforms.

Using Microsoft's async HttpClient PCL library has been troublesome.

In fact, it is Xamarin error messages which are buried, especially for iOS compilation (it should be better for the next release). It works perfectly with no problem. Just never install the HttpClient PCL package in your ios/android project, only in pcl projects. Just reference System.Http from mono in android/ios. And also never add the Microsoft.Bcl package in your ios/android project (ignore the warning).

Shamnad · April 2014

can anyone can help me to retriving value from a server using json webservice

Shamnad · April 2014

anyone can help me to retriving value from a server using json webservice

RichardHopkins · May 2014

@Shamnad‌

I'm assuming you're asking how to communicate with a web service by both sending and receiving json.

Here's a bare bones method that should be enough for you to modify it to your needs.

public static async Task<string> SendAndReceiveJsonRequest()
{
    string responseStr = null;
    string uri = "uri-to-send-the-data-to";

    // Create a json string with a single key/value pair.

    var json = new JObject(new JProperty("json-key-name", value)).ToString();

    using (var httpClient = new HttpClient())
    {        
        //create the http request content

        HttpContent content = new StringContent(json);

        try
        {
            // Send the json to the server using POST

            Task<HttpResponseMessage> getResponse = httpClient.PostAsync(uri, content);
            // Wait for the response and read it to a string var

            HttpResponseMessage response = await getResponse;
            responseStr = await response.Content.ReadAsStringAsync();
        }
        catch (Exception e)
        {
            Console.WriteLine("Error communicating with the server: " + e.Message);
        }
    }
    return responseStr;
}

You'll probably need to add references to your project for json.net and system.net.http. I'm assuming you can parse the json once it's returned.

h8tow8 · May 2014

can anyone help me to understand why when I use similar code to Richard's I get the following error:

{System.Net.WebException: Error: ConnectFailure (Connection timed out) ---> System.Net.Sockets.SocketException: Connection timed out
at System.Net.Sockets.Socket.Connect (System.Net.EndPoint remoteEP) [0x00000] in :0
at System.Net.Web...

I post the same json string to the same url using fiddler and have no problems but does not matter what i do i always get this error calling PostAsync from android.

SKall · May 2014

Are you trying to call a service on a localhost? If so, try address 10.0.2.2 instead of localhost or 127.0.0.1. If not, check that you can connect to the address in question from the Android device.

h8tow8 · May 2014

Sami, thank you for your advise that got me thinking ;~).
I was 100% convinced that these is something to do with android/xamarin and portable libraries i use but it turned out the firewall on my windows.

PriyabrataDash · June 2014

I faced in adding the Microsoft HttpClient Libraries reference to Xamarin Studio using NuGet Pachage manager.
After a lot of digging I found out the problem is with "Target Frameworks" Build options.
If you have checked "Silverlight 4" as a target Framework for your project you may face Adding reference issue.
If this is the case with you simply go to 'Project->Options->Build->General->Under Target Framework, untick Silverlight 4 option.

Just refresh the Project & Build. It worked for me.

MikeKenyon.7267 · June 2014

I am having no success with 10.0.2.2, is there something else to try?

MartinUshima · July 2014

@h8tow8 did you try in a device?

I'm getting the same error, (ConnectFailure (Connection timed out)), when using HttpClient and testing in a device.

h8tow8 · July 2014

my problem was silly - i had a firewall turned on on a pc where the web service was running ;~)
once i disabled it - all was good

MartinUshima · July 2014

Fixed.

It was a DNS setting and the IT area help me solve it.

Thanks!

Shamnad · December 2014

hai guys,

          i have a problem on populating table view in xamarin ios 
          i have a string in an url, which is like this (25*SALADS*36.png$28*OMELETTE*36.png$29*PASTA*36.png$30*MEAT  DISHES*36.png$32*SALADS*food2.png$33*SOUPS*food.png$)

i need to populate table view using this String i can fetch the data to an array
but how can i populate table view using that array?

this is my code in controller

    using System;
    using System.CodeDom.Compiler;
    using System.Collections.Generic;
    using System.Drawing;
    using System.Net;
    using System.Threading;
    using System.IO;
    using System.Net.Http;
    using System.Collections;
    using System .Linq; 
    using System.Diagnostics;
    using System.Threading.Tasks;
    using MonoTouch.Foundation;
    using MonoTouch.UIKit;
    namespace project
    {

public class cm_item
    {
        // category id
        public int cat_id { get; set; }
        // category Name 
        public string cat_name { get; set; }
        // image url from server
        public string cat_url { get; set; }
    }

        partial class specialViewController : UIViewController
        { 
            cm_item[]ns;//total records  
            public specialViewController (IntPtr handle) : base (handle)
            {

            }     
            public async override void ViewDidLoad()
            {
                base.ViewDidLoad();              
                var table = new UITableView (new RectangleF (0, 0, View.Bounds.Width, View.Bounds.Height));

                View.Add (table);

                Task<string> siz = getall ();           //  progress.Show(); 
            //    var s = await siz; 
            } 
            /// <summary>
            /// async data loading.
            /// </summary>

            async Task<string> getall() 
            { 
                var req = "http://xam.dimindserver.co.in/category/display?id=1";// calling the string from the url 
                HttpClient client = new HttpClient ();
                Task<string> getStringTask = client.GetStringAsync (req);
                string urlContents = await getStringTask;
                if (urlContents != "") {
                    int inc = 0;
                    int totalRec = Convert.ToInt32 (urlContents.Split ('$').Count ());
                    ns = new cm_item[totalRec - 1];
                    foreach (System.String  mans in  urlContents.Split('$')) {
                        if (mans != "") {
                            System.String[] singCate = mans.ToString ().Split ('*');
                            if (singCate.Count () != 0) {                            
                                cm_item Cm_Cate = new  cm_item ();
                                Cm_Cate.cat_id = Convert.ToInt32 (singCate [0].ToString ());                    //id form db 
                                Cm_Cate.cat_name = singCate [1].ToString ();  
                                Cm_Cate.cat_url = singCate [2];
                                ns [inc] = Cm_Cate; 
                                inc++; 
                            }

                        }
                      }  
                    };

                return "True"; 

                } 

            }
            }

i have another Class for data source

    using System;
    using System.Drawing;

    using MonoTouch.Foundation;
    using MonoTouch.UIKit;

    namespace project
    {
        public class itemsTableSource:UITableViewSource
        {
            cm_item[] _category;
            UINavigationController _controller;
            string cellIdentifier = "TableCell";

            public itemsTableSource (cm_item[] category, UINavigationController controller)
            {
                _category = category;
                _controller = controller;
            }
            public override int RowsInSection (UITableView tableview, int section)
            {
                return _category.Length;
            }
            public override UITableViewCell GetCell (UITableView tableView, NSIndexPath indexPath)
            {
                UITableViewCell cell = tableView.DequeueReusableCell("TableCell");
                if (cell == null) {
                    cell = new UITableViewCell (UITableViewCellStyle.Subtitle, "TableCell");
                }

                cell.TextLabel.Text = _category[indexPath.Row].cat_name;
                cell.Accessory = UITableViewCellAccessory.DetailDisclosureButton;
                return cell;
            }
        }


    }

how can i populate table view using that array

Shamnad · December 2014

i got my error ..with help of some other friends............

SagarPanwala · August 2016

@MartinUshima : Can you please tell me in detail , how you have fixed it? I'm facing this connect failure issue on user device also.

MartinUshima · August 2016

@SagarPanwala, the scenario that I was facing was that the services that I was consuming were outside my company network. So, I talked with the IT guys in my company, specified them the IPs addresses and URLs that I was trying to connect to. They register that info in the allowed or trusted source and that was it.

It had nothing to do with code, just network settings.

The issue is that those settings are managed by the IT area, nothing to do with me.

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