BackgroundTransferRequest WP7

问题

I am using the Background Transfer to upload Photographs to my Web Service. As the Photograph uploads can consume significant time and memory, I thought it might be a nice idea to use the background transfer request to accomplish this. After the photo is uploaded, I want to obtain the Id of the uploaded photo and then use it for post-processing. However, it turns out I can't do that in a background transfer request.

Per my understanding, Background Transfer works using the following logic ONLY:

You have to obtain the file you want to upload and then save/copy it to your app's Isolated Storage under the folder: shared/transfers. This is extremely important. Apparently, using file in a different location didn't work for me. Maybe it isn't the shared/transfers as much as it is a 'relative' path. But I would stick to the same conventions.
After you have saved the file in that location, your background request can be created based on that. It doesn't look like you can pass POST CONTENT other than the file contents, so any other parameters like file name, mime type etc. will need to be passed as QUERY String parameters only. I can understand this, but it would've been nice if I could pass both as POST Content. I don't think HTTP has a limitation on how this works.

Here is some code for creating a request using Hammock:

string url = App.ZineServiceAuthority + "articles/save-blob?ContainerName={0}&MimeType={1}&ZineId={2}&Notes={3}&IsPrivate={4}&FileName={5}";
url = String.Format(url, userId, "image/jpg", ZineId, txtStatus.Text, true, UploadFileName);

var btr = new BackgroundTransferRequest(new Uri(url, UriKind.Absolute));
btr.TransferPreferences = TransferPreferences.AllowCellularAndBattery;
btr.Method = "POST";
btr.Headers.Add("token", IsolatedStorageHelper.GetTravzineToken());
btr.UploadLocation = new Uri(@"/shared\transfers/" + UploadFileName, UriKind.Relative);
btr.TransferStatusChanged += new EventHandler<BackgroundTransferEventArgs>(btr_TransferStatusChanged);
btr.TransferProgressChanged += new EventHandler<BackgroundTransferEventArgs>(btr_TransferProgressChanged);

BackgroundTransferService.Add(btr);

In my case, I am literally passing all the necessary parameters using the query string. On a successful save, my Web Service returns back the Id of the Photo I just uploaded. However: There is NO way (or at least I know of) to obtain and evaluate the RESPONSE. The Background Transfer Request Event handlers do not expose a RESPONSE. Here are my event handlers:

void btr_TransferProgressChanged(object sender, BackgroundTransferEventArgs e)
{
    bool isUploading = e.Request.TotalBytesToSend > 0 ? true : false;
    lblStatus.Text = isUploading ? "Uploading" + e.Request.BytesSent.ToString() + " sent" : "Done";
}

void btr_TransferStatusChanged(object sender, BackgroundTransferEventArgs e)
{
    if (e.Request.TransferStatus == TransferStatus.Completed)
    {

        using (IsolatedStorageFile iso =
               IsolatedStorageFile.GetUserStoreForApplication())
        {
            if (iso.FileExists(e.Request.UploadLocation.OriginalString))
                iso.DeleteFile(e.Request.UploadLocation.OriginalString);
        }

        BackgroundTransferService.Remove(e.Request);

        if (null != e.Request.TransferError)
        {
            MessageBox.Show(e.Request.TransferError.Message);
        }
        else
        {
            lblStatus.Text = "Done baby done";
        }

    }
}

So now my question is, how does anyone do any sort of POST Processing in such scenarios? Can anyone please tell me the line of thought behind designing such an inflexible class? Any thoughts on how I could get around this issue would be appreciated.

Also, does anyone have any working examples of a homegrown BackgroundTransfer?

回答1:

Haven't tried it but why not set a download location like this:

btr.DownloadLocation = "myDownloadFile.html";
btr.UploadLocation = "myUploadFile.jpg";
...

If the request is completed read the file "myDownloadFile.html" where your response has been stored and delete it afterwards.

来源：https://stackoverflow.com/questions/7936144/backgroundtransferrequest-wp7

标签

windows-phone-7

wcf-web-api