problems in silverlight 4 when using Action callbacks to check for successful file upload

So the async requirement for silverlight ends up in some really convoluted code!!

Im uploading a file just exactly like this answer suggests.

The difference is Im posting the file to an MVC action method. Everything works file except, like I commented on the bottom of that answer, I don't get any callback for when the file DOES NOT successfully upload.

So I created another action method in my mvc app (Services/CheckForFile/{id}) and it returns a string depending on whether the file is found.

Now, how and when do I call this mvc action method is the problem:

  void DoUpload() { //Gets call on BtnUpload.Click
              //opn is an OpenFileDialog
            up.UploadFile(_filename, opn.File.OpenRead(),
                e =>
                {
                 //do some ui stuff here.
                  BeginCheck();// calling this causes PROBLEMS!  
                });
    }
    private void BeginCheck()
    {
        Uploader up = new Uploader();
        up.CheckForFile(_filename, success =>
        {
            if (!success)
            {
                MessageBox.Show("There was problem uploading the file. Please try again", "Error", MessageBoxButton.OK);
            }
        });
    }

Here is the problem: When the BeginCheck() function runs, the file, for some reason, NEVER uploads! If I comment it out it does!? It seems like The BeginCheck() runs during the upload or something? Shouldn't it run after!?

How/where would I call BeginCheck() after the upload, to ensure the file has been uploaded?

Here is how I defined the Uploader class:

 public class Uploader
    {
        public void UploadFile(string fileName, Stream data, Action<Exception> callback)
        {
            UriBuilder ub = new UriBuilder(_mvcurl+"Services/UploadFile/" + fileName);
            WebClient c = new WebClient();
            c.OpenWriteCompleted += (sender, e) =>
            {
                try
                {
                    PushData(data, e.Result);
                    e.Result.Close();
                    data.Close();  //this does not block.
                    callback(null);//this ALWAYS hits!
                }
                catch (Exception err)
                {
                    if (callback != null)
                    {
                        callback(err);
                    }
                }
            };
            c.OpenWriteAsync(ub.Uri);
        }
        public void CheckForFile(string filename, Action<bool> callback)
        {
            UriBuilder ub = new UriBuilder(_mvcurl+"Services/CheckForFile/" + fileName);
            WebClient c = new WebClient();
            c.OpenReadCompleted += (sender, e) =>
                {
   开发者_如何学运维                 using (StreamReader sw = new StreamReader(e.Result))
                    {
                        if (sw.ReadToEnd().Equals("Found", StringComparison.InvariantCultureIgnoreCase))
                        {
                            callback(true);
                        }
                        else
                        {
                            callback(false);
                        }
                    }
                };
            c.OpenReadAsync(ub.Uri);
        }
        private void PushData(Stream input, Stream output)
        {//4KB is not a limitation. We only copy 4Kb at a time from in to out stream
            byte[] buffer = new byte[4096];
            int bytesRead;
            while ((bytesRead = input.Read(buffer, 0, buffer.Length)) != 0)
            {
                output.Write(buffer, 0, bytesRead);
            }
        }
    }

---

I'm embarrased to say that the original answer of mine to which you refer isn't entirely accurate. It seems to work for what the OP wanted but in fact the code doesn't block at the point that I thought it did. In reality what you are actually looking for is the WriteStreamClosed event, its here that you can discover any failure of the request.

Here is an ammended version that works the way you are expecting:-

        public void UploadFile(string fileName, Stream data, Action<Exception> callback)
        {
            UriBuilder ub = new UriBuilder(_mvcurl+"Services/UploadFile/" + fileName);
            WebClient c = new WebClient();
            c.OpenWriteCompleted += (sender, e) =>
            {
                try
                {
                    PushData(data, e.Result);
                    e.Result.Close();
                    data.Close();  //this does not block.
                }
                catch (Exception err)
                {
                    if (callback != null)
                        callback(err);
                }
            };
            c.WriteStreamClosed += (sender, e) =>
            {
                if (callback != null)
                    callback(e.Error);
            }
            c.OpenWriteAsync(ub.Uri);
        }

Now your BeginCheck will only run after the server has responded to the file upload.