使用TextFieldParser从流中解析CSV始终达到EndOfData

Question

在将Azure Blob中的CSV文件解析为流时，TextFieldParser将始终直接到达EndOfData，而不会读取任何数据。相同的代码，但路径相同的物理文件，而不是流的作品。

Dim storageAccount As CloudStorageAccount = CloudStorageAccount.Parse(AzureStorageConnection) 
    Dim blobClient As CloudBlobClient = storageAccount.CreateCloudBlobClient() 
    Dim BlobList As IEnumerable(Of CloudBlockBlob) = blobClient.GetContainerReference("containername").ListBlobs().OfType(Of CloudBlockBlob) 

    For Each blb In BlobList 
     Dim myList As New List(Of MyBusinessObject) 

     Using memoryStream = New MemoryStream() 
      blb.DownloadToStream(memoryStream) 

      Using Reader As New FileIO.TextFieldParser(memoryStream) 
       Reader.TextFieldType = FileIO.FieldType.FixedWidth 
       Reader.SetFieldWidths(2, 9, 10) 
       Dim currentRow As String() 
       While Not Reader.EndOfData 
        Try 
         currentRow = Reader.ReadFields() 
         myList.Add(New GsmXFileRow() With { 
         ' code to read currentRow and add elements to myList 
         }) 
        Catch ex As FileIO.MalformedLineException 
        End Try 
       End While 
      End Using 
     End Using 
    Next 

我也试图MemoryStream转换为TextReader

Dim myTextReader As TextReader = New StreamReader(memoryStream) 

，然后传递到myTextReaderTextFieldParser，但这也不管用。

Using Reader As New FileIO.TextFieldParser(myTextReader)

Answer 1

我看到这一点：

长度属性的值等于文件大小

这：

“Position`酒店有相同的值

这意味着在循环开始时，MemoryStream已经进入流结束。只需将Position设置回0，你应该处在一个更好的位置。

但是，这里也可能存在另一个问题。该流数据是二进制的，有一些未知的编码。 TextFieldParser想与Text一起工作。您需要一种方法来提供有关使用哪种编码的信息。

在这种情况下，我推荐StreamReader。这种类型的TextReader继承，这样你就可以与TextFieldParser使用它：

Dim storageAccount As CloudStorageAccount = CloudStorageAccount.Parse(AzureStorageConnection) 
Dim blobClient As CloudBlobClient = storageAccount.CreateCloudBlobClient() 
Dim BlobList As IEnumerable(Of CloudBlockBlob) = blobClient.GetContainerReference("containername").ListBlobs().OfType(Of CloudBlockBlob) 

Dim myList As New List(Of MyBusinessObject) 
For Each blb In BlobList 

    'Several constructor overloads allow you to specify the encoding here 
    Using blobData As New StreamReader(New MemoryStream()) 
     blb.DownloadToStream(blobData.Stream) 

     'Fix the position problem 
     blobData.Stream.Position = 0 

     Using Reader As New FileIO.TextFieldParser(blogData) 
      Reader.TextFieldType = FileIO.FieldType.FixedWidth 
      Reader.SetFieldWidths(2, 9, 10) 
      Dim currentRow As String() = Reader.ReadFields() 
      While Not Reader.EndOfData 
       Try 
        myList.Add(New GsmXFileRow() With { 
         ' code to read currentRow and add elements to myList 
        }) 
        currentRow = Reader.ReadFields() 
       Catch ex As FileIO.MalformedLineException 
       End Try 
      End While 
     End Using 
    End Using 
Next