How to return some values from an asynchronous Task

Question

I'm uploading a file using multipart data form and I need to keep the file description of the uploaded file. I'm using the following code

FileDescription temp = new FileDescription();
var task = Request.Content.ReadAsMultipartAsync(streamProvider).ContinueWith<IEnumerable<FileDescription>>(t =>
{

    if (t.IsFaulted || t.IsCanceled)
    {
        throw new HttpResponseException(HttpStatusCode.InternalServerError);
    }

    var fileInfo = streamProvider.FileData.Select(i =>
    {
        var info = new FileInfo(i.LocalFileName);
        temp.AssociatedSchool = 1;
        temp.FileName = info.Name;
        temp.LocalFileName = i.LocalFileName;
        temp.FileSize = info.Length / 1024;
        temp.IsFileValid = true;
        temp.NoOfRecords = 1;
        temp.UploadedBy = 1;
        return temp;
    });
    return fileInfo;
});

This code doesnt set the values to the temp object. Can anyone tell me an alternate way to get the values? task.Result is always null. How can i get the values out of the thread?

what is a type of streamProvider? and it's FileData property — potehin143, Jan 16 '14 at 07:26
@potehin143 type is MultipartFormDataStreamProvider. I tried your answer, its not working. I need the value of file description used with the task for another variable. Is that possible? — NewBie, Jan 16 '14 at 07:31
It's strange that you trying to process collection (FileData) but use the same local var temp. What do you want to see in results? The collection if FileDescriptors? or single FileDescriptor for the First element of FileData? — potehin143, Jan 16 '14 at 07:42

score 1 · Answer 1 · answered Jan 16 '14 at 08:18

Try change your sample like this

var descriptions = Request.Content.ReadAsMultipartAsync(streamProvider)
                          .ContinueWith<IEnumerable<FileDescription>>(t =>
            {
                if (t.IsFaulted || t.IsCanceled)
                {
                    throw new HttpResponseException(HttpStatusCode.InternalServerError);
                }

                var fileInfo = streamProvider.FileData.Select(i =>
                {
                    var info = new FileInfo(i.LocalFileName);
                    return new FileDescription(){
                        AssociatedSchool = 1;
                        FileName = info.Name;
                        LocalFileName = i.LocalFileName;
                        FileSize = info.Length / 1024;
                        IsFileValid = true;
                        NoOfRecords = 1;
                        UploadedBy = 1;
                    }
                });
                return fileInfo;
            }).Result;

var temp = descriptions.First();//Possibly you need FirstOrDefault

How to return some values from an asynchronous Task

1 Answers1