启动调试后生成的错误如何解决的问题（4）

Question

在启动调试后出现了下面的问题。错误提示是：未声明名称“ISDBNULL”。不知道怎么解决。已知db.vb是连接字符串的类文件。

Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click


        Dim strsql, course As String
        Dim conn As New constr.db
        Dim i, courseid As Integer
        strsql = "select max(id) as maxno from klgpointab"
        Dim dr As SqlDataReader
        Dim myconn As New SqlConnection(conn.getstr)
        Dim mycommand1 As New SqlCommand(strsql, myconn)
        myconn.Open()
        dr = mycommand1.ExecuteReader()
        dr.Read()
        If IsDBNull(dr.Item(0)) Then
            i = 0
        Else
            i = dr.Item(0) + 1
        End If
        dr.Close()
        Dim dr1 As SqlDataReader
        course = Session("coursename")
        strsql = "select courseid from courseinfo where coursename='" & course & "'"
        Dim mycommand2 As New SqlCommand(strsql, myconn)
        dr1 = mycommand2.ExecuteReader
        If dr1.Read() Then
            courseid = dr1.Item(0)
        End If
        dr1.Close()
        strsql = "insert into klgpointab(id,chapter,knowledgepoint,coursename) values("
        strsql = strsql & i & ","
        strsql = strsql & courseid * 100 + j & ",'"
        strsql = strsql & TextBox1.Text & "',"
        strsql = strsql & "'" & course.ToString().Trim() & "')"
        Dim mycommand3 As New SqlCommand(strsql, myconn)
        mycommand3.ExecuteNonQuery()
        j = j + 1
        TextBox1.Text = ""
        myconn.Close()
        mycommand1.Dispose()
        mycommand2.Dispose()
        mycommand3.Dispose()
        myconn.Dispose()
    End Sub

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qianghuishi

Answer 1

改用DBNull.Value来判断

  Private Function IsDBNull(ByVal obj As Object) As Boolean
        Dim result = False

        If DBNull.Value.Equals(obj) Then
            result = True
        End If

        Return result

End Function

http://msdn.microsoft.com/zh-cn/library/system.dbnull(v=vs.90).aspx#Y746

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• Convert C# to VB.NET
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Answer 2

楼主，关于你的连接字符串和DBNull的问题照例是可以的，但是我无法重现你的错误，请直接看这个帖子：http://social.msdn.microsoft.com/Forums/zh-CN/295/thread/393fd9d3-fdea-4803-9aab-d8d0258810a7

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Answer 3

您好。在引入这个函数后，ISDBNULL确实没有问题了，但是您看：这里的Private Sub出现了问题。不知道怎么回事？

Public Shared j As Integer = 1
    Private Function IsDBNull(ByVal obj As Object) As Boolean
        Dim result = False


        If DBNull.Value.Equals(obj) Then
            result = True
        End If


        Return result




    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click

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qianghuishi

Answer 4

有缘人好！在改过dr.Item（0）=DBNull.Value之后错误消失了但出现了没有为System.DBNull定义运算符“=”的提示，下面是一条蓝线的的提示，应该还是有问题的吧？

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qianghuishi

Answer 5

有缘人好！在改过dr.Item（0）=DBNull.Value之后错误消失了但出现了没有为System.DBNull定义运算符“=”的提示，下面是一条蓝线的的提示，应该还是有问题的吧？

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qianghuishi

把=改成Is

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   QQ我：
下载MSDN桌面工具(Vista,Win7)
我的博客园
慈善点击，点击此处