异步，等待EventHandler返回值

Question

我正在尝试使用适用于.Net的AWS Sdk将文件上传到S3bucket。
我正在上传如下文件：

Private Async Sub Button1_Click(sender As Object, e As EventArgs) Handles Button2.Click

   Await AddFileToFolderAsync(file, bucketName, fld) 
   ' here file is  file's fullpath,buckatename is  
   ' available s3bucket name, 
   ' fld is target folder path into that s3bucket.
End Sub


Public Async Function AddFileToFolderAsync(FileName As String, bucketName As String, folderName() As String) As Task
    Try
        If Not AmazonS3Util.DoesS3BucketExistV2(S3client, bucketName) Then
            MessageBox.Show("Bucket does not exist")
            Dim fname() As String = folderName
            CreateFolder(bucketName, fname)
        Else
            Dim keyname As String = "" 'destination path(s3 bucket folder)
            Dim filepath As String = FileName 'current file's local fullpath
            Dim fname As String = Path.GetFileName(FileName) 'filename

            For i = 0 To folderName.Length - 1
                keyname += folderName(i) & "/"
            Next

            keyname += fname  'bucket's target folder /fname (eg:folder/subfolder/file.mp4)

            Dim fileTransferUtility = New TransferUtility(S3client)
            Dim fileTransferUtilityRequest = New TransferUtilityUploadRequest With {
                .BucketName = bucketName,
                .FilePath = filepath,
                .StorageClass = S3StorageClass.Standard,
                .ServerSideEncryptionMethod = ServerSideEncryptionMethod.None,
                .PartSize = 6291456,
                .Key = keyname,
                .ContentType = "*.*"}

            AddHandler fileTransferUtilityRequest.UploadProgressEvent, New EventHandler(Of UploadProgressArgs)(AddressOf UploadRequest_UploadPartProgressEvent)
            Await fileTransferUtility.UploadAsync(fileTransferUtilityRequest)
        End If
    Catch ex As AmazonS3Exception
        MessageBox.Show(ex.Message + " Upload task canceled.")
    Catch ex As Exception
        MessageBox.Show(ex.Message + " Upload task canceled.")
    End Try
End Function

上面的代码中有事件处理程序：

AddHandler fileTransferUtilityRequest.UploadProgressEvent, New EventHandler(Of UploadProgressArgs)(AddressOf UploadRequest_UploadPartProgressEvent)

它确实：

Public Function UploadRequest_UploadPartProgressEvent(ByVal sender As Object, ByVal e As UploadProgressArgs)
   ' here uploadprogressargs class has two variable which are having 
   ' totalbytes and transferedbytes(those are e.transferedbytes and e.totalbytes)
End Function

现在，我的问题是：如何基于ProgrssValue增加e.TransferredBytes？

希望大家都能理解我的问题。我是.Net的初学者。