问来自Task.Continuewith的新任务(在单独的线程上运行)

EN

private void btnNew_Click(object sender, RoutedEventArgs e)
{
// do some work and prepare transfer state object(my custom object)
...
..
  iTaskFactory = new TaskFactory
          (TaskCreationOptions.LongRunning | TaskCreationOptions.AttachedToParent,
           TaskContinuationOptions.None);

// call transfer manager
this.ManageTransfer(null, iDownloadState);
}

private void ManageTransfer(Task antecedent, TransferState ts)
{
  if(antecedent == null)
  // this is the first invocation of the task from GetNew / Upload methods
  {
    ts.IsActive = true;
    // some code....
  }
  else if(antecedent.IsFaulted)       // check exception on previous task executed
  // if there is a fault, then retry the page again
  {

    // do some error logging....
    //retry transferring the same page again
    pageToTranfer = ts.PagesTransferred + 1;
  }
  else
  // if the page was successfully transferred
  {
    //increment transfer count
    ts.PagesTransferred += 1;

    // update UI.... (as running on UI Thread)

    // if all pages are transferred, then exit method. No further tasks to queue
    if(ts.PagesTransferred == ts.Pages)
    {          
      return;
    }

    pageToTranfer = ts.PagesTransferred + 1;
  }

  Task transferTask;     // should run in background thread
                         // **Problem is that afer first execution**, 
                         // **this also runs on UI Thread!!**
  Task continuationTask; // should run in UI thread

    localFile = "someName.txt";  //..... work out next file to transfer
    serverFile = "someName.txt"; //..... work out next file to transfer

  time = DateTime.Now.ToString("hh:mm:ss.ffff"); //.ToShortTimeString();    
  Debug.WriteLine(time + "starting download :" + pageToTranfer.ToString() 
                  + " This is Thread: " 
                  + Thread.CurrentThread.ManagedThreadId.ToString());

  transferTask = iTaskFactory.StartNew(() => Download(serverFile, localFile));

  continuationTask = transferTask.ContinueWith((t1Task) => ManageTransfer(t1Task, ts)
                     , TaskScheduler.FromCurrentSynchronizationContext());

}

public bool Download(string aCloudPath, string aLocalPath)
{

  time = DateTime.Now.ToString("hh:mm:ss.ffff"); //.ToShortTimeString();
  Debug.WriteLine(time + " in background for downloading " 
                 + aCloudPath + " using thread:" 
                 + Thread.CurrentThread.ManagedThreadId.ToString());

  // code to transfer file... no access to UI or any shared variable

  return true;
}