在vb.net中读取文件错误?

这个文件的工作方式是有一个空缓冲区,然后是一个用户校验和,然后是一个字节,它给出用户名字母计数,然后是一个字节,表示要跳到下一个用户的字节数,以及一个字节,表示用户将其设置保存在哪个用户文件中。

if语句中带有usersm变量的循环将设置整个文件流以进行提取。然而,对于几乎完全相同的代码,else子句(特别是else代码中的str.read(xnl,0,usn-1))似乎正在读取文件的最开始部分,尽管之前设置了文件流的位置,但有人知道这里发生了什么吗?

这是在vb2005

Private Sub readusersdata(ByVal userdatafile As String)
    ListView1.BeginUpdate()
    ListView1.Items.Clear()
    Using snxl As IO.Stream = IO.File.Open(userdatafile, IO.FileMode.Open)

        Using str As New IO.StreamReader(snxl)
            str.BaseStream.Position = 4
            Dim usersm As Integer = str.BaseStream.ReadByte()
            Dim users As Integer = usersm
            While users > 0
                If usersm = users Then
                    Dim trailtouser As Integer = 0
                    str.BaseStream.Position = 6
                    Dim ust As Integer = str.BaseStream.ReadByte()
                    str.BaseStream.Position = 8
                    Dim snb(ust - 1) As Char
                    str.ReadBlock(snb, 0, ust)
                    Dim bst = New String(snb)
                    If usersm = 1 Then
                        str.BaseStream.Position = 16
                    Else
                        str.BaseStream.Position = 15
                    End If
                    cLVN(ListView1, bst, str.BaseStream.ReadByte)
                    str.BaseStream.Position = 8 + snb.Length
                    str.BaseStream.Position += str.BaseStream.ReadByte + 1
                Else

                    Dim usn As Integer = str.BaseStream.ReadByte
                    str.BaseStream.Position += 2
                    Dim chrpos As Integer = str.BaseStream.Position
                    Dim xnl(usn - 1) As Char
                    str.Read(xnl, 0, usn - 1)
                    Dim skpbyte As Integer = str.BaseStream.ReadByte
                    str.BaseStream.Position += 3
                    Dim udata As Integer = str.BaseStream.ReadByte


                End If

                users -= 1

            End While
        End Using
    End Using
    ListView1.EndUpdate()
End Sub