WP8 で WebRequest を使うとき、GetResponse() を await したいよね!

Downloader1.cs

private static Task<WebResponse> GetResponseAsync(WebRequest request)
{
    return Task.Run<WebResponse>(() =>
        {
            AutoResetEvent autoResetEvent = new AutoResetEvent(false);

            // BeginGetResponse で autoResetEvent を発火させる
            IAsyncResult asyncResult = request.BeginGetResponse(r => autoResetEvent.Set(), null);

            // autoResetEvent.Set() の発火を待つ。すなわちここでブロックする
            autoResetEvent.WaitOne();

            return request.EndGetResponse(asyncResult);
        });
}

Downloader2.cs

var uri = new Uri("http://hoge.moge...");
string result;

var req = HttpWebRequest.Create(uri);
using (var res = await GetResponseAsync(req))
using (var stream = res.GetResponseStream())
using (var rdr = new StreamReader(stream))
{
    result = await rdr.ReadToEndAsync();
}