Facebook C# SDK throws ArgumentNullException

问题

I'm struggling with the facebook image upload. I'm using the Facebook C# SDK 5.4.1 to upload a picture from my Silverligth 5 Application (in Browser).

Authentication is working and I get my access token with the needed permissions. (I'm storing my access token in a cookie because I don't want my Silverlight App to reload.)

This is my code:

void img_LoadingCompleted(object sender, EventArgs e)
    {

        Dispatcher.BeginInvoke(new Action(() => { string fbcode = ReadCookie("FBCode");

        ExtendedImage img = sender as ExtendedImage;
        string myAppId = "MY_APPID";
        string myAppSecret = "MY_SECRET";

        FacebookClient fbclient = new FacebookClient(fbcode);
        fbclient.PostCompleted += new EventHandler<FacebookApiEventArgs>(fbclient_PostCompleted);

        FacebookMediaObject image = new FacebookMediaObject
        {
            ContentType = "image/jpg",
            FileName = "Testpic"
        };
        image.SetValue(img.Pixels);

        IDictionary<string, object> photoDetails = new Dictionary<string, object>
            {
                {"message", "Test"},
                {"source", image}
            };

        fbclient.PostAsync("/me/photos", photoDetails);
        }));
    }

    void fbclient_PostCompleted(object sender, FacebookApiEventArgs e)
    {
        if (e.Cancelled)
        {
            Dispatcher.BeginInvoke(new Action(() =>
            {
                MessageBox.Show("Cancelled: "+e.Error);
            }));
        }
    }

The exception is thrown in the PostCompleted event of the FacebookClient.

{System.ArgumentNullException: Der Wert darf nicht NULL sein.
Parametername: stream
   bei System.IO.StreamReader..ctor(Stream stream, Encoding encoding, Boolean detectEncodingFromByteOrderMarks, Int32 bufferSize, Boolean leaveOpen)
   bei System.IO.StreamReader..ctor(Stream stream)
   bei Facebook.FacebookClient.ProcessResponse(HttpHelper httpHelper, Stream responseStream, Type resultType, String& responseStr, Exception& exception, Boolean& cancelled)}

Thanks for your help.

回答1:

I figured out the problem myself.

If the encoding of the image is wrong you'll get the ArgumentNullException because Facebook simply doesn't not respond. I also tried this solution (tweaked the code a little bit because Silverlight 5 doesn't support WriteableBitmap.SaveJpeg()) and the HTTP Error 404 was the response I got.

If anyone else encouters a similar problem (and is confused as I was :-)) maybe I can help with the following solution (using Facebook C# SDK 5.4.1 and Silverlight 5 In-Browser):

JpegEncoder JE = new JpegEncoder();
MemoryStream M = new MemoryStream();
JE.Encode(Img.ToImage(), M);

Byte[] ImgData = new Byte[M.Length];
M.Seek(0, SeekOrigin.Begin);
M.Read(ImgData, 0, (int)M.Length);

FacebookClient fbclient = new FacebookClient(fbcode);
fbclient.UploadProgressChanged += new EventHandler<FacebookUploadProgressChangedEventArgs>(fbclient_UploadProgressChanged);
fbclient.PostCompleted += new EventHandler<FacebookApiEventArgs>(fbclient_PostCompleted);

FacebookMediaObject image = new FacebookMediaObject
{
    ContentType = "image/jpg",
    FileName = "Testpic"
};
image.SetValue(ImgData);

IDictionary<string, object> photoDetails = new Dictionary<string, object>
{
     {"message", "Test"},
     {"source", image}
};

new Thread(new ParameterizedThreadStart((fbc) => { StartWait(); ((FacebookClient)fbc).PostAsync("me/photos", photoDetails); })).Start(fbclient);

Where the variable Img is a WriteableBitmap. For the right encoding I'm using the Imagetools from Codeplex

NOTICE: You need a valid access_token to get this working!

来源：https://stackoverflow.com/questions/9392016/facebook-c-sharp-sdk-throws-argumentnullexception

标签

facebook-c#-sdk