等待Windows Phone 7上的WebRequest

Question

I'm doing some work with Google APIs in Windows Phone 7 using OAuth2.

Before I can make a call to the API I need to update the access token (if required).

The issue I'm having is waiting for the async request updating the token to finish before proceeding with call to the API.

I've got it working with the code below, but I'm not happy with it. I'm looking for a better alternative to simply polling a variable in a while loop.

    /// <summary>
    /// Calls the API.
    /// </summary>
    /// <param name="callback">The callback.</param>
    /// <param name="api">The API.</param>
    /// <param name="queryStrings">The query strings.</param>
    public static void CallApi(AsyncCallback callback, string api, Dictionary<string, string> queryStrings = null)
    {
        var uri = new Uri(string.Format("{0}{1}{2}", ApiBaseUrl, api, queryStrings.ToQueryString()));

        if (accessTokenExpires < DateTime.Now.AddSeconds(300))
        {
            RefreshAccessToken();
        }

        // Start new thread so we don't lock up the UI thread while waiting
        var thread = new Thread(
            () =>
                {
                    // Wait for the access token to be updated
                    while (accessTokenExpires < DateTime.Now.AddSeconds(300)) ;

                    var request = WebRequest.CreateHttp(uri);
                    request.Headers["Authorization"] = string.Format("OAuth {0}", accessToken);
                    request.BeginGetResponse(callback, request);
                });

        thread.Start();
    }

    /// <summary>
    /// Refresh the access token.
    /// </summary>
    private static void RefreshAccessToken()
    {
        if (Config.GoogleOAuthRefreshToken == string.Empty)
        {
            // TODO - Present the OAuth popup to the user
            return;
        }

        var uri = new Uri(GetTokenUrl);

        var request = WebRequest.CreateHttp(uri);
        request.Method = "POST";
        request.ContentType = "application/x-www-form-urlencoded";

        request.BeginGetRequestStream(RefreshToken_GetRequest, request);
    }

Answer 1

I think you have the beginnings of what you need, but just need to use the Async nature of the WebRequest to it's fullest. Here is an example of how this can be done

public static void CallApi(AsyncCallback callback, string api, Dictionary<string, string> queryStrings = null)
{
    var uri = new Uri(string.Format("{0}{1}{2}", ApiBaseUrl, api, queryStrings.ToQueryString()));

    RefreshAccessToken(() =>
        {
            var request = WebRequest.CreateHttp(uri);
            request.Headers["Authorization"] = string.Format("OAuth {0}", accessToken);
            request.BeginGetResponse(callback, request);
        });
}

private static void RefreshAccessToken(Action callback)
{
    if(IsTokenExpired() == false)
    {
        if(callback != null) callback();
        return;
    }
    if (Config.GoogleOAuthRefreshToken == string.Empty)
    {
        // TODO - Present the OAuth popup to the user
        return;
    }

    var uri = new Uri(GetTokenUrl);

    var request = WebRequest.CreateHttp(uri);
    request.Method = "POST";
    request.ContentType = "application/x-www-form-urlencoded";

    request.BeginGetRequestStream(asyncResult =>
    {
        // Do anything for POST
        request.BeginGetResponse(asyncResult2 =>
        {
            // Read stream, and process
            if(callback != null) callback();
        }, null);
    }, request);
}

private bool IsTokenExpired()
{
    return accessTokenExpires < DateTime.Now.AddSeconds(300);
}

Answer 2

Have you considered using the Async-CTP or VS 2012 to convert this logic into a Task.Delay call? It can probably even help with your web request code.