vb.net - VB：.Net Core - 尽管定义了结构并初始化了结构，但在使用结构时获取“未设置对象引用”

Question

我似乎遇到了在命令行 Visual Basic .NET (core 5) 项目中使用结构的问题。在其中我有一个处理命令队列/缓冲系统的类。

这是类代码：

Public Class ClassCommandBuffer

' CmdMax is the maximum number of commands allowed within a set (0 to CmdMax -1)
Public Const MaxCmdSets As Integer = 30
Public Const MaxNoofCmdLines As Integer = 30

' CurrentNestIndex contains the current nest level. If this is set to -1 then buffer comamnds aren't being run
' NestedMaxIndex is the maximum number of nested buffer command sets allowed (0 to NextedMax -1)
' CmdMax is the maximum number of commands allowed within a set (0 to CmdMax -1)

Public Structure CmdBufferCmdStruct
    Public CmdLines() As String     ' Array of Command Lines within current set
    Public NoofCmds As Integer      ' Number of Command Lines
    Public CurrentIndex As Integer  ' Usually set to -1, but if cmdset being run then reflects the current cmd index
End Structure

Public Structure CmdBufferLoadingStruct
    Public Index As Integer         ' When loading a command set in, this will be set to the new command set index, otherwise it's -1
    Public CmdIndex As Integer      ' When loading a commadn set in, this is the command index of the next command to be loaded, otherwise -1
End Structure

Public Structure CmdBufferStruct
    Public Loading As CmdBufferLoadingStruct        ' Used when loading a new command set
    Public CmdSet() As CmdBufferCmdStruct           ' Array of command sets 
    Public CurrentNestIndex As Integer              ' Current nested index being processed
End Structure

Public CmdBuffer As CmdBufferStruct




' --- Initialise values & setup ---
Public Sub New()
    ReDim CmdBuffer.CmdSet(MaxCmdSets)                              ' declates 30 sets
    ReDim CmdBuffer.CmdSet(MaxCmdSets).CmdLines(MaxNoofCmdLines)    ' declates 30 sets of 30 cmds each
    CmdBuffer.CurrentNestIndex = -1                                 ' initialise the current nest index to -1 (buffer cmds not running)
    CmdBuffer.Loading.Index = -1
    CmdBuffer.Loading.CmdIndex = 0
    Console.WriteLine("> New")
End Sub

' --- Command Sets ---
Public Sub NewCmdSetStart()
    Console.WriteLine("> NewCmdSetStart")
    With CmdBuffer
        .Loading.Index = .CurrentNestIndex + 1
        .Loading.CmdIndex = 0
    End With
End Sub

Public Sub NewCmdSetEnd()
    Console.WriteLine("> NewCmdSetEnd")
    With CmdBuffer
        .CmdSet(.Loading.Index).NoofCmds = .Loading.CmdIndex
        .Loading.Index = -1
        .CurrentNestIndex = .CurrentNestIndex + 1
    End With
End Sub

Public Sub NewCmdSetInsert(newcmd As String)
    Console.WriteLine("> NewCmdSetInsert : " & newcmd)
    With CmdBuffer
        .CmdSet(.Loading.Index).CmdLines(.Loading.CmdIndex) = newcmd
        Dim x As Integer = .Loading.CmdIndex + 1
        .Loading.CmdIndex = x
    End With
End Sub

' --- Command processing ---
Public Function GetNextCmd() As String
    ' check to see if we've hit the end cmds or not running from buffer
    If CmdBuffer.CurrentNestIndex = -1 Then
        Console.WriteLine("Error: We're not running buffer commands! Why was GetNextCmd called? Line " & CMDlineCount)
        EndAssembler()
    End If

    Dim CurCmdLine As Integer = CmdBuffer.CmdSet(CmdBuffer.CurrentNestIndex).CurrentIndex
    Dim CurCmdNoof As Integer = CmdBuffer.CmdSet(CmdBuffer.CurrentNestIndex).NoofCmds

    If CurCmdLine >= CurCmdNoof Then
        Console.WriteLine("Error: We've reach the end of cmds! Why was GetNextCmd called? Should check before calling. Line " & CMDlineCount)
        EndAssembler()
    End If

    Return CmdBuffer.CmdSet(CmdBuffer.CurrentNestIndex).CmdLines(CurCmdLine)
End Function

Public Function IsBufferRunning() As Boolean
    If CmdBuffer.CurrentNestIndex = -1 Then Return False Else Return True
End Function

结束类

该类在 MainModule 中定义，因此：

Module ModuleMain

Public CommandBuffer As New ClassCommandBuffer

Sub Main(args As String())

调用代码如下所示：

        With ModuleMain.CommandBuffer
            .NewCmdSetStart()
            .NewCmdSetInsert(ifCmd)
            .NewCmdSetEnd()
        End With

IfCmd 是一个字符串变量，其中包含要存储的命令。

我遇到的问题是，当调用“ NewCmdSetInsert(ifCmd) ”时，它在函数内的行上崩溃：“ Dim x As Integer = .Loading.CmdIndex + 1 ”并出现以下错误：“ System. NullReferenceException：“对象引用未设置为对象的实例。” '原来的说法是

            .Loading.CmdIndex = .Loading.CmdIndex + 1

但是我用临时的 Dim x... 行将其分开，以尝试查看问题出在哪里。

似乎是说我没有将结构定义为新的，但我在 MainModule 中有。此外，在类的“新建”部分中，我为 .Loading.CmdIndex 设置了一个初始值，我不太明白问题是什么，因为我得到以下输出，表明“新建”首先运行（因此初始化数组和值）：此时它因上述错误而中断并突出显示（忽略“BCC 20480”，因为这是传递给 NewCmdSetInsert 的命令字符串）

新的

NewCmdSetStart

新命令集插入：密件抄送 20480

有人有什么想法吗？

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