如何在VB中的代码中的其他地方调用变量？

Question

所以，我有以下VB代码：

Try
        Using verSR As New StreamReader(appDataVersionLoc)
            Dim txtVern As String
            txtVern = verSR.ReadToEnd()
        End Using
    Catch ex As Exception
        Dim verFile As System.IO.FileStream
        verFile = System.IO.File.Create(appDataVersionLoc)
        My.Computer.FileSystem.WriteAllText("appDataVersionLoc", "0.0.0.0", True)
        MessageBox.Show("Version file missing/corrupt, created a new one.")
    End Try

看到名为“txtVern？”的变量我试图在Try-End Try块之外的代码中的其他地方使用它。 差不多这个：

Try
        Using verSR As New StreamReader(appDataVersionLoc)
            Dim txtVern As String
            txtVern = verSR.ReadToEnd()
        End Using
    Catch ex As Exception
        Dim verFile As System.IO.FileStream
        verFile = System.IO.File.Create(appDataVersionLoc)
        My.Computer.FileSystem.WriteAllText("appDataVersionLoc", "0.0.0.0", True)
        MessageBox.Show("Version file missing/corrupt, created a new one.")
    End Try

    blahblahblahblahblahblahblahblahblahblahblahblahblahblahblahblahblahblahblahblahblahblahblahblahblahblahblahblahblahblahblah

    Dim currentversion As String = txtVern

现在，我是一个完整的VB菜鸟，我收到了这个错误：

  

'txtVern'未声明。由于它可能无法访问   保护水平。

我该如何解决这个问题？ 谢谢！

Answer 1

在任何块内声明的变量仅在该块内可见。您必须在Try阻止之前移动声明：

Dim txtVern As String = String.Empty
Try
    Using verSR As New StreamReader(appDataVersionLoc)
        txtVern = verSR.ReadToEnd()
    End Using
Catch ex As Exception
    Dim verFile As System.IO.FileStream
    verFile = System.IO.File.Create(appDataVersionLoc)
    My.Computer.FileSystem.WriteAllText("appDataVersionLoc", "0.0.0.0", True)
    MessageBox.Show("Version file missing/corrupt, created a new one.")
End Try

blahblahblahblahblahblahblahblahblahblahblahblahblahblahblahblahblahblahblahblahblahblahblahblahblahblahblahblahblahblahblah

Dim currentversion As String = txtVern

Answer 2

在try块中声明变量txtVern时，您将其范围限制为try块。尝试在子例程的开头声明它们。