Question

以下是我的代码

Class LIVandOSA
    Public LIV_ As String
    Public OSA_ As String
End Class

Class TestUnitID
    Public SMPSdata As LIVandOSA
    Public SMdata As LIVandOSA
    Public COATEDBARdata As LIVandOSA
    Public CLCLdata As LIVandOSA

    Public Sub New(ByVal s As String)
        SMPSdata.LIV_ = s
    End Sub
End Class

在主程序中，我编写了以下代码来创建TestUnitID列表并在其中添加一些元素。

    Dim a As New List(Of TestUnitID)
    a.Add(New TestUnitID("a1.csv"))
    a.Add(New TestUnitID("a2.csv"))
    TextBox1.Text = a(0).SMPSdata.LIV_

但是当我尝试编译它时，它会给我以下错误

An unhandled exception of type 'System.NullReferenceException' occurred in WindowsApplication1.exe

Additional information: Object reference not set to an instance of an object.

错误光标指向行SMPSdata.LIV_(s)

我该如何解决此错误？

Answer 1

错误是不言自明的，您尚未初始化该对象。

由于您在构造函数中，因此它是初始化字段和属性的好地方：

Class TestUnitID
    Public SMPSdata As LIVandOSA
    Public SMdata As LIVandOSA
    Public COATEDBARdata As LIVandOSA
    Public CLCLdata As LIVandOSA

    Public Sub New(ByVal s As String)
        Me.SMPSdata = New LIVandOSA()
        Me.SMdata = New LIVandOSA()
        Me.COATEDBARdata = New LIVandOSA()
        Me.CLCLdata = New LIVandOSA()

        SMPSdata.LIV_(s)
    End Sub
End Class

Answer 2

您应该在使用对象之前启动它，因此您可以使用

Me.SMPSdata = New LIVandOSA()
...

创建新对象

如何创建一个类，其中一个对象是VB中另一个类的类型？

2 个答案: