Get progress of an async call

Question

I'm using a block of code I got from a blog, to upload images to IMGur using API v3.

It works fine, but I wanted to implement a progress bar system to let the user know how much has been uploaded, if the program deals with high res images.

So far I haven't been able to do so.

I'm not an experienced coder, just doing this as a learning project.

The Code:

public object UploadImage(string image) 
{ 
    WebClient w = new WebClient();
    w.UploadProgressChanged += (s, e) => { };
    w.UploadValuesCompleted += (s, e) => { };
    w.Headers.Add("Authorization", "Client-ID " + ClientId);
    System.Collections.Specialized.NameValueCollection Keys = new System.Collections.Specialized.NameValueCollection(); 
    try 
    { 
        Keys.Add("image", Convert.ToBase64String(File.ReadAllBytes(image))); 
        byte[] responseArray = w.UploadValues("https://api.imgur.com/3/image", Keys);


        dynamic result = Encoding.ASCII.GetString(responseArray); System.Text.RegularExpressions.Regex reg = new System.Text.RegularExpressions.Regex("link\":\"(.*?)\""); 
        System.Text.RegularExpressions.Match match = reg.Match(result); 
        string url = match.ToString().Replace("link\":\"", "").Replace("\"", "").Replace("\\/", "/");
        textBox1.Text = url;
        return url; 
    }
    catch (Exception s) 
    { 
        MessageBox.Show("Something went wrong. " + s.Message); 
            return "Failed!"; 
    } 
}

At first I tried using the events UploadProgressChanged and UploadValuesCompleted, but they are not triggered, my theory is they are triggered when UploadValuesAsync is called instead of UploadValues.

1. How do I implement a progress system?
2. What is the difference between async and normal transfer?

Answer 1

The difference between aync and normal transfer is, that the UploadValues method will block the current thread until all data has been transferred. Because the thread is blocked in this time you can't catch any events too. Therefore you have to use the asynchrony method UploadValuesAsync which will transfer the data in the background and you're able to go on with the execution of your code.
The UploadProgressChanged only fires for the UploadValuesAsync too. Your code should look something like this (Not tested!):

public String UploadImage(string image) 
    { 
        WebClient w = new WebClient();

        w.UploadProgressChanged += (s, e) =>
        {
            myProgressBar.Maximum = (int)e.TotalBytesToSend;
            myProgressBar.Value = (int)e.BytesSent;
        };

        w.UploadValuesCompleted += new UploadValuesCompletedEventHandler(UploadComplete);

        w.Headers.Add("Authorization", "Client-ID " + ClientId);
        System.Collections.Specialized.NameValueCollection Keys = new System.Collections.Specialized.NameValueCollection(); 
        try 
        { 
            Keys.Add("image", Convert.ToBase64String(File.ReadAllBytes(image))); 
            w.UploadValuesAsync("https://api.imgur.com/3/image", Keys);

            return "Uploading..";
        } catch (Exception s) 
        { 
            MessageBox.Show("Something went wrong. " + s.Message); 
                return "Failed!"; 
        } 
    }

public void UploadComplete(Object sender, UploadValuesCompletedEventArgs e)
{
    myProgressBar.Value = 100;

    byte[] responseArray = e.Result;
    dynamic result = Encoding.ASCII.GetString(responseArray); 
    System.Text.RegularExpressions.Regex reg = new System.Text.RegularExpressions.Regex("link\":\"(.*?)\""); 
    System.Text.RegularExpressions.Match match = reg.Match(result); 
    string url = match.ToString().Replace("link\":\"", "").Replace("\"", "").Replace("\\/", "/");
    textBox1.Text = url;
}

Edit
I moved the code after the UploadValuesAsync call into the w.UploadValuesCompleted. You can find the server response in the Result field of the UploadValuesCompletedEventArgs class which is passed to the event in the variable e.
Your method UploadImage will now return Uploading when the progress started and you'll have to do your rest work in the w.UploadValuesCompleted event.