警告变量“csCryptoStream”在被赋值之前被使用。运行时可能会导致空引用异常

Question

我是 VB.Net 的新手。我正在尝试调试我的项目，但收到警告：变量“csCryptoStream”在被赋值之前已被使用。运行时可能会导致空引用异常

我该如何解决？

Private Sub EncryptOrDecryptFile(strInputFile As String, strOutputFile As String, bytKey As Byte(), bytIV As Byte(), Direction As crypt.CryptoAction)
    ' The following expression was wrapped in a checked-statement
    Try
        Me.fsInput = New FileStream(strInputFile, FileMode.Open, FileAccess.Read)
        Me.fsOutput = New FileStream(strOutputFile, FileMode.OpenOrCreate, FileAccess.Write)
        Me.fsOutput.SetLength(0L)
        Dim bytBuffer As Byte() = New Byte(4096) {}
        Dim lngBytesProcessed As Long = 0L
        Dim lngFileLength As Long = Me.fsInput.Length
        Dim cspRijndael As RijndaelManaged = New RijndaelManaged()
        Me.pbStatus.Value = 0
        Me.pbStatus.Maximum = 100
        Dim csCryptoStream As CryptoStream
        Select Case Direction
            Case crypt.CryptoAction.ActionEncrypt
                csCryptoStream = New CryptoStream(Me.fsOutput, cspRijndael.CreateEncryptor(bytKey, bytIV), CryptoStreamMode.Write)
            Case crypt.CryptoAction.ActionDecrypt
                csCryptoStream = New CryptoStream(Me.fsOutput, cspRijndael.CreateDecryptor(bytKey, bytIV), CryptoStreamMode.Write)
        End Select
        While lngBytesProcessed < lngFileLength
            Dim intBytesInCurrentBlock As Integer = Me.fsInput.Read(bytBuffer, 0, 4096)

Warning --->     csCryptoStream.Write(bytBuffer, 0, intBytesInCurrentBlock)
            ' The following expression was wrapped in a unchecked-expression
            lngBytesProcessed += CLng(intBytesInCurrentBlock)
            ' The following expression was wrapped in a unchecked-expression
            Me.pbStatus.Value = CInt(Math.Round(CDec(lngBytesProcessed) / CDec(lngFileLength) * 100.0))
        End While

Answer 1

1. 如下声明CryptoStream：

    Dim csCryptoStream As CryptoStream = Nothing
   

2. 在Case/Select 中添加“Case Else”子句

3. 在使用此变量之前检查是否

   If Not IsNothing(csCryptoStream)
     '    ....
   End If