Question

I’m trying to make a simple class for my REST calls so I won’t have the same code in multiple places in my application.

The problem is, I don’t know how to notify an object that called the UploadStringAsync() method from inside the UploadStringCompleted() event handler.

Here is my class, I have added comments to mark the place where I want to notify the object from which the Post method has been called:

using System;
using System.Net;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Documents;
using System.Windows.Ink;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Animation;
using System.Windows.Shapes;

namespace MyProject.Utils
{
    public class Rest
    {
        private WebClient client = new WebClient();

        private void Init()
        {
            client.UploadStringCompleted += new UploadStringCompletedEventHandler(client_UploadStringCompleted);
        }

        public void Post(string uri, string postRequest, object objectToNotify)
        {
            Init();
            client.Headers["Content-Type"] = "application/x-www-form-urlencoded";
            client.UploadStringAsync(new Uri(uri,
                UriKind.RelativeOrAbsolute), "POST", postRequest, objectToNotify);
        }

        private void client_UploadStringCompleted(object sender,
           UploadStringCompletedEventArgs e)
        {
            // here I would like to notify an object from 
            // which the Post() method has been called
            // I don't know how to do this as this method has no idea
            // which object called the method
            // this doesn't work:
            // (e.UserState.GetType())e.UserState.RestCallback(e);
        }
    }
}

EDIT:

My modified code after Jacob’s suggestions:

using System;
using System.Net;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Documents;
using System.Windows.Ink;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Animation;
using System.Windows.Shapes;
using System.Windows.Browser;

namespace MyProject.Utils
{
    public class Rest
    {
        private WebClient client = new WebClient();

        private void Init()
        {
            client.UploadStringCompleted += new UploadStringCompletedEventHandler(client_UploadStringCompleted);
        }

        public void Post(
            string uri, string postRequest,
            Action<UploadStringCompletedEventArgs> callback)
        {
            HtmlPage.Window.Alert("bbb");
            client.Headers["Content-Type"] = "application/x-www-form-urlencoded";
            client.UploadStringAsync(new Uri(uri,
                UriKind.RelativeOrAbsolute), "POST", postRequest, callback);
        }

        private void client_UploadStringCompleted(object sender,
           UploadStringCompletedEventArgs result)
        {
            HtmlPage.Window.Alert("aaa");
            var callback = (Action<UploadStringCompletedEventArgs>)result.UserState;
            callback(result);
        }
    }
}

This is how I’m calling the Post method:

    string postRequest = "id=5":
    Rest restClient = new Rest();
    restClient.Post("http://mywebsite.com/", postRequest, RestCallback);

    .......................

    private void RestCallback(UploadStringCompletedEventArgs result)
    {
        if (result.Error != null)
        {
            ContactFormSuccess.Text = "There was an error sending email message.";
        }
        else
        {
            ContactFormSuccess.Text = "Email message successfully sent.";
        }
    }

Answer 1

You could modify your Rest class so that it’s given a callback delegate rather than the object to notify. It could look something like this:

public void Post(
    string uri, string postRequest, 
    Action<UploadStringCompletedEventArgs> callback)
{
    Init();
    client.Headers["Content-Type"] = "application/x-www-form-urlencoded";
    client.UploadStringAsync(
        new Uri(uri, UriKind.RelativeOrAbsolute), 
        "POST", postRequest, callback);
}

private void client_UploadStringCompleted(object sender,
   UploadStringCompletedEventArgs e)
{
    var callback = (Action<UploadStringCompletedEventArgs>)e.UserState;
    callback(e);
}

Then, when you make the request, the call would look something like this:

var restClient = new Rest();
restClient.Post("http://your/url", "stuff", handleResult);


// ...

private void handleResult(UploadStringCompletedEventArgs result)
{
}