Async HTTP Post data in single function using Async CTP

Question

I'm trying use Async CTP to build single function that run async and return a value.

here is my sample code. i don't know why it dont fill the "resp" variable at return.

public async Task<string> sendRequest(string url, string postdata)
{
    WebClient client = new WebClient();
    byte[] data = Encoding.UTF8.GetBytes(postdata);
    Uri uri = new Uri(url);
    client.UploadDataAsync(uri,"POST", data);
    string resp = "";
    await TaskEx.Run(()=>
    client.UploadDataCompleted += (e, s) =>
    {
        resp = System.Text.Encoding.UTF8.GetString(s.Result);
    });
    return resp;
}

Also I tried this but the program freeze ( do nothing more not just for a while ). maybe any correction can help.

public async Task<string> sendRequest(string url, string postdata)
{
    string resp = "";
    WebClient client = new WebClient();
    byte[] data = Encoding.UTF8.GetBytes(postdata);
    Uri uri = new Uri(url);
    data = await TaskEx.Run(()=>client.UploadData(uri,"POST", data));

    return System.Text.Encoding.UTF8.GetString(data);
}

Answer 1

You could, instead, use the UploadDataTaskAsync extension method (part of the CTP), and not have to write that plumbing code yourself:

public async Task<string> sendRequest(string url, string postdata)
{
    WebClient client = new WebClient();
    byte[] data = Encoding.UTF8.GetBytes(postdata);
    Uri uri = new Uri(url);
    resp = System.Text.Encoding.UTF8.GetString(await client.UploadDataTaskAsync(uri,"POST", data));
    return resp;
}

The implementation of that extension method handles the event subscription correctly, and ensures that the task is completed when the event actually fires.