Vb.net 使用另一个类的属性访问一个类将返回空值

我正在制作一个应用程序，从通过串行电缆连接到我的计算机的仪表中读取数值。当我按下一个按钮时，我会向仪表发送一个命令，几毫秒后，仪表会回复我的答案。 我将这些值保存到具有init属性的类中，以便可以从任何地方访问这些值

因此，我的问题是，当我试图取回这些值时，它返回一个“nothing value”，这可能是因为我的初始化中有一个“New”像这样“Dim clsSavedValues As New clsSavedValues”，因此，当我试图从属性类中获取值时，我创建了一个新实例，如果我没有弄错的话，该实例是空的

我将在下面发布代码，但以下是代码的流程： 我有三节课。MainClass、ProtocolClass、PropertieClass。 我从main调用ProtocolClass中的一个方法，该方法向meter发送一个命令。几毫秒后，我在ProtocolClass内部收到一个回调，该方法称为“私有Sub-SerialPort_DataReceived”（ByVal sender作为对象，ByVal e作为System.IO.Ports.SerialDataReceivedEventArgs），它处理SerialPort.DataReceived，并将返回值保存到PropertiesClass。 DataReceived方法完成后，我返回main类并调用另一个方法，从我刚刚保存的PropertiesClass中获取值，但返回null。我知道它们被正确保存，因为如果我从ProtocolClass中调用它们，我可以访问它们。但它们在MainClass中为空

这是我的密码： MainClass

'Here i call the ProtocolClass
 Private Sub btnGetLastTransaction_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnGetLastTransaction.Click
        clsProtocol.GetLastTransaction(1, Integer.Parse(tbxTransactionPosition.Text))
    End Sub

'Here i try to read the valies from PropertiesClass
    Public Sub RetrieveMeterSerialNumber()
        Dim clsSavedValues As New clsSavedValues
        lblMeterSerialNumber.Text = clsSavedValues.SaveMeterSerialNumber
    End Sub

 Public Sub GetLastTransaction(ByVal destinationAddress As String, ByVal transactionNum As Integer)
        clsSavedValues = New clsSavedValues 'Creating Instance of the properties class
        Try
            Dim v_bodyOfMessage As [Byte]() = {ASCIItoHEX("G"), _
                                               ASCIItoHEX("r")}
            Dim v_bytearray As [Byte]() = ConstructCommand(v_bodyOfMessage)

            SendCommand(v_bytearray)
        Catch ex As Exception
            Console.WriteLine("Meter serial number button click exception: {0}", ex)
        End Try
    End Sub

Private Sub SerialPort_DataReceived(ByVal sender As Object, ByVal e As System.IO.Ports.SerialDataReceivedEventArgs) Handles SerialPort.DataReceived
    If comOpen Then
        Try
            ReDim rx(rxPacketSize)
            Console.WriteLine("RESPONSE")
            For i = 0 To rxPacketSize - 1
                readByte = SerialPort.ReadByte.ToString
                Console.WriteLine(i.ToString & ": " & Conversion.Int(readByte).ToString)
                rx(i) = Conversion.Int(readByte).ToString

                If i <> 0 Then
                    If Convert.ToByte(rx(i)) = vDelimeterFlag(0) Then Exit For
                End If
            Next
            DecodeResponse()
        Catch ex As Exception
            MsgBox("SerialPort_DataReceived Exception: " & ex.Message)
        End Try
    End If
End Sub

Private Sub GetMeterSerialNumber()
    Dim i_startPosition As Integer = 5
    Dim meterSerialNumber As String = GetRemainingPortionOfString(i_startPosition)
    clsSavedValues.SaveMeterSerialNumber = meterSerialNumber
    frmExplorer.RetrieveMeterSerialNumber() 'This is the call to the main class
End Sub

Public Property SaveMeterSerialNumber() As String
    Get
        Return _MeterSerialNumber
    End Get
    Set(ByVal meterSerialNumber As String)
        _MeterSerialNumber = meterSerialNumber
    End Set
End Property

协议类

'Here i call the ProtocolClass
 Private Sub btnGetLastTransaction_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnGetLastTransaction.Click
        clsProtocol.GetLastTransaction(1, Integer.Parse(tbxTransactionPosition.Text))
    End Sub

'Here i try to read the valies from PropertiesClass
    Public Sub RetrieveMeterSerialNumber()
        Dim clsSavedValues As New clsSavedValues
        lblMeterSerialNumber.Text = clsSavedValues.SaveMeterSerialNumber
    End Sub

 Public Sub GetLastTransaction(ByVal destinationAddress As String, ByVal transactionNum As Integer)
        clsSavedValues = New clsSavedValues 'Creating Instance of the properties class
        Try
            Dim v_bodyOfMessage As [Byte]() = {ASCIItoHEX("G"), _
                                               ASCIItoHEX("r")}
            Dim v_bytearray As [Byte]() = ConstructCommand(v_bodyOfMessage)

            SendCommand(v_bytearray)
        Catch ex As Exception
            Console.WriteLine("Meter serial number button click exception: {0}", ex)
        End Try
    End Sub

Private Sub SerialPort_DataReceived(ByVal sender As Object, ByVal e As System.IO.Ports.SerialDataReceivedEventArgs) Handles SerialPort.DataReceived
    If comOpen Then
        Try
            ReDim rx(rxPacketSize)
            Console.WriteLine("RESPONSE")
            For i = 0 To rxPacketSize - 1
                readByte = SerialPort.ReadByte.ToString
                Console.WriteLine(i.ToString & ": " & Conversion.Int(readByte).ToString)
                rx(i) = Conversion.Int(readByte).ToString

                If i <> 0 Then
                    If Convert.ToByte(rx(i)) = vDelimeterFlag(0) Then Exit For
                End If
            Next
            DecodeResponse()
        Catch ex As Exception
            MsgBox("SerialPort_DataReceived Exception: " & ex.Message)
        End Try
    End If
End Sub

Private Sub GetMeterSerialNumber()
    Dim i_startPosition As Integer = 5
    Dim meterSerialNumber As String = GetRemainingPortionOfString(i_startPosition)
    clsSavedValues.SaveMeterSerialNumber = meterSerialNumber
    frmExplorer.RetrieveMeterSerialNumber() 'This is the call to the main class
End Sub

Public Property SaveMeterSerialNumber() As String
    Get
        Return _MeterSerialNumber
    End Get
    Set(ByVal meterSerialNumber As String)
        _MeterSerialNumber = meterSerialNumber
    End Set
End Property

我想从PropertiesClass中获取这些值，因为我会从仪表中获得超过wan的响应，这会导致线程问题，我无法跟踪它们。所以我把这些值保存在一个类中，然后我想从那个类中访问它们。

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很抱歉写了这么长的文章，请询问我任何需要澄清的问题。

SerialPort_DataReceived（）和主类RetrieveMeterSerialNumber（）中的clsSavedValues是两个不同的对象（具有相同的变量名，但每个“new”都创建了一个新的clsSavedValues实例）也许您应该将clsSavedValues变量作为参数从协议传递到Main

主要内容：

  Public Sub RetrieveMeterSerialNumber(clsSavedValues As clsSavedValues )
        lblMeterSerialNumber.Text = clsSavedValues.SaveMeterSerialNumber
    End Sub

协议：

Private Sub GetMeterSerialNumber()
    Dim i_startPosition As Integer = 5
    Dim meterSerialNumber As String = GetRemainingPortionOfString(i_startPosition)
    clsSavedValues.SaveMeterSerialNumber = meterSerialNumber
    frmExplorer.RetrieveMeterSerialNumber(clsSavedValues) 'This is the call to the main class
End Sub

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或者在PropertiesClass中使用静态属性

如果只想为应用程序域（exe）存储一个值，则需要使用静态属性。在这种情况下没有必要做出“新的”，只需引用类propertyit就相当简单了。我没有想到这一点谢谢伊曼纽尔：）