Question

我试图为一个arrayList分配一个类的实例，但是它给了我以下错误。

Object reference not set to an instance of an object.

这是我分配的代码。

Public memberList As ArrayList

Public Sub LoadUser()
Dim userId As Integer = 0
    Dim userData As Data.DataTable = oExecuteSimpleQuery_DT("QA", "SELECT * FROM Member")
    If userData IsNot Nothing Then
        For Each user As Data.DataRow In userData.Rows
            If memberList(userId) Is Nothing Then
                memberList(userId) = 1
            End If
            memberList(userId) = New clsMember(user("UserID"), user("Firstname"), user("Secondname"), user("Username"), user("Password"), user("Email"), user("Rights"))
            userId += 1
        Next
    End If
End Sub

Answer 1

在您的问题中显示的代码中，您确实声明了memberList变量，但是您没有创建实例。要解决错误，请将第一行更改为：

Public memberList As New ArrayList()

两个侧节点：

不要使用ArrayList，而是查看List(Of T)。它提供了几乎相同的功能，但输入结构很强。
NullReferenceException是一个值得理解的常见错误。有关原因和解决方法的详细信息，请参阅此link。

Answer 2

试试这个：

Public memberList as New List(Of clsMember)


Public Sub LoadUser()
 Dim userId As Integer = 1
 Dim userData As Data.DataTable = oExecuteSimpleQuery_DT("QA", "SELECT * FROM Member")
 If userData IsNot Nothing Then
    For Each user As Data.DataRow In userData.Rows
        memberList.Add(New clsMember(user("UserID"), user("Firstname"), user("Secondname"), user("Username"), user("Password"), user("Email"), user("Rights"))
        userId += 1
    Next
 End If
End Sub

创建类的实例时出错

2 个答案: