.net 为什么此性能监视器代码失败

这段代码过去可以工作，现在它抛出异常并拒绝工作。代码没有改变。我怀疑原因是我将磁盘分区以添加第二个分区。其目的是监视其自身路径所在的物理驱动器的空闲时间百分比

    Try
        Dim drive As String = BunzipInputStream.BinDirectory.Substring(0, 2)
        Dim instname As String = Nothing
        If drive.EndsWith(":"c, StringComparison.Ordinal) Then
            Dim dix = New System.Diagnostics.PerformanceCounterCategory
            dix.CategoryName = "PhysicalDisk"
            For Each px In dix.GetInstanceNames()
                If px.EndsWith(drive, StringComparison.OrdinalIgnoreCase) Then
                    instname = px
                End If
            Next
            diskcounter = New System.Diagnostics.PerformanceCounter()
            diskcounter.CategoryName = "PhysicalDisk"
            diskcounter.CounterName = "% Idle Time"
            diskcounter.InstanceName = instname
            diskcounter.NextValue()
        End If
    Catch ex As Exception
        'ENDS UP HERE AND ABORTS THE MONITOR
        If Not diskcounter Is Nothing Then
            diskcounter.Dispose()
            diskcounter = Nothing
        End If
    End Try

（这是设置代码。如果diskcounter.NextValue（）不可显示，则有一个计时器会调用它）

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正如Hans Passant在评论中所说，您的变量instname可能没有按照您的预期进行设置

哪一个？我可以阅读任何.NET家族。@TomaszNurkiewicz它已经被标记为.NET。虽然代码是VB，但问题很可能与任何特定于VB的内容无关。引发的异常是什么？这可能会有所帮助：For循环未找到匹配项，因此instname变量仍然为空。很容易在调试器中看到。那么，@HansPassant应该提供一个答案吗？或者，至少是问题的作者是的。汉斯需要提供答案。

System.InvalidOperationException occurred
  Message=Counter is not single instance, an instance name needs to be specified.
  Source=System
  StackTrace:
       at System.Diagnostics.PerformanceCounter.NextSample()
       at System.Diagnostics.PerformanceCounter.NextValue()
       at Redacted.PerformanceMon.OnHandleCreated(EventArgs e) in C:\development\redacted\redacted\Forms\PerformanceMon.vb:line XX
  InnerException: