Visual Studio Vb.net |USB检测代码部分工作

问：

我不得不重写帖子，因为 stackoverflow 检测到该帖子已经在另一个线程中解决，我不得不删除它。但是引用论坛的线程是针对 C# 的，无论如何，即使阅读它，我也无法找到解决我的问题的方法。

所以，大家好，:D

我确实在网上的某个地方找到了一个代码，可以让我检测 USB 设备和相关文件， 它有效但不是很好，因为每次我插入或拔出 USB 设备时，我都会得到：

“System.NullReferenceException”，我不会写其余的错误以避免stackoverflow关闭线程，无论如何你应该已经理解我的问题。

代码如下：

Imports System.IO
Public Class Form1
#Region "USB EVENT"

    Private WM_DEVICECHANGE As Integer = &H219

    Public Enum WM_DEVICECHANGE_WPPARAMS As Integer
        DBT_CONFIGCHANGECANCELED = &H19
        DBT_CONFIGCHANGED = &H18
        DBT_CUSTOMEVENT = &H8006
        DBT_DEVICEARRIVAL = &H8000
        DBT_DEVICEQUERYREMOVE = &H8001
        DBT_DEVICEQUERYREMOVEFAILED = &H8002
        DBT_DEVICEREMOVECOMPLETE = &H8004
        DBT_DEVICEREMOVEPENDING = &H8003
        DBT_DEVICETYPESPECIFIC = &H8005
        DBT_DEVNODES_CHANGED = &H7
        DBT_QUERYCHANGECONFIG = &H17
        DBT_USERDEFINED = &HFFFF
    End Enum

    Private Structure DEV_BROADCAST_VOLUME
        Public dbcv_size As Int32
        Public dbcv_devicetype As Int32
        Public dbcv_reserved As Int32
        Public dbcv_unitmask As Int32
        Public dbcv_flags As Int16
    End Structure

    Protected Overrides Sub WndProc(ByRef m As System.Windows.Forms.Message)

        Try
            If m.Msg = WM_DEVICECHANGE Then

                Dim Volume As DEV_BROADCAST_VOLUME

                Volume = DirectCast(Runtime.InteropServices.Marshal.PtrToStructure(m.LParam, GetType(DEV_BROADCAST_VOLUME)), DEV_BROADCAST_VOLUME)

                If Not GetDriveLetterFromMask(Volume.dbcv_unitmask).ToString.Trim = String.Empty Then

                    Dim DriveLetter As String = (GetDriveLetterFromMask(Volume.dbcv_unitmask) & ":\")

                    Select Case m.WParam

                        Case WM_DEVICECHANGE_WPPARAMS.DBT_DEVICEARRIVAL

                            LblUSB.Text = DriveLetter

                            GetFiles()
                            MsgBox("Usb connected")
                            '   Code When add USB

                        Case WM_DEVICECHANGE_WPPARAMS.DBT_DEVICEREMOVECOMPLETE

                            LblUSB.Text = ""

                            CheckedListBox1.Items.Clear()
                            MsgBox("Usb disconnected")
                            '   Code When Remove USB

                    End Select

                End If

            End If

        Catch ex As Exception

        End Try

        MyBase.WndProc(m)

    End Sub

    Private Function GetDriveLetterFromMask(ByRef Unit As Int32) As Char
        For i As Integer = 0 To 25
            If Unit = (2 ^ i) Then
                Return Chr(Asc("A") + i)
            End If
        Next
        Return ""
    End Function

#End Region

    Sub GetFiles()

        Try

            Dim Path = LblUSB.Text

            Dim LstFiles = My.Computer.FileSystem.GetFiles(Path, FileIO.SearchOption.SearchTopLevelOnly)

            For Each File In LstFiles
            Dim F As New IO.FileInfo(File)
            CheckedListBox1.Items.Add(F.Name)
        Next

        Catch ex As Exception

        End Try

    End Sub
End Class

我得到的System.NullReferenceException是在这一点上：

 Volume = DirectCast(Runtime.InteropServices.Marshal.PtrToStructure(m.LParam, GetType(DEV_BROADCAST_VOLUME)), DEV_BROADCAST_VOLUME)

我确实读到过，当值为 null 并且应该有一个关联的值时，会发生此错误， 我尝试了不同的方法，但没有一个奏效，我希望你们中的某个人能给我一个解决方案和解释，以更好地理解这一点。

非常感谢你们的帮助！