Question

我正在尝试学习VB.NET，我正在寻找从Access 2010视图中检索数据，使用Vb.NET 2008，问题是我收到以下错误。 System.ArgumentNullException未处理Message = Value不能为null

我无法弄清楚如何解决错误，所以希望有更多经验的人可以提供帮助。

Public Function GetMyoleDataAdapterStudentQuestionRepeat(ByRef mydataSet As DataSet, ByVal topicId As String, ByVal groupId As String) As OleDbDataAdapter
            Try
                Dim strAccessConn As String = _appConfigDbConn
                Dim cn As OleDbConnection = New OleDbConnection(strAccessConn)
                Dim ds As New DataSet
                Dim da As New OleDbDataAdapter("qryStudentNameRandomBasedOnScore", cn)
                da.SelectCommand.CommandType = CommandType.StoredProcedure
                da.SelectCommand.Parameters.AddWithValue("@GroupID", groupId)
                da.Fill(ds, "Student")
                Return da
            Catch ex As Exception
                Throw New ApplicationException(ex.InnerException.Message.ToString())
            End Try
        End Function

在按钮内单击

Dim myoleDataAdapter As OleDbDataAdapter = GroupData.GetMyoleDataAdapterStudentQuestionRepeat(mydataSet, topicId, groupId)
            myoleDataAdapter.Fill(mydataSet)
            txtStudentName.DataBindings.Add("Text", mydataSet.Tables(0), "studentname")

此行抛出错误：myoleDataAdapter.Fill（mydataSet）

如果有帮助，我的观点是

SELECT TOP 1 tblStudentNameAndScore.studentname
FROM tblStudentNameAndScore
WHERE (((tblStudentNameAndScore.[QuizCount]) Between 2 And 10)) AND  tblStudentNameAndScore.GroupID = ?
ORDER BY Rnd(QuizCount);

感谢任何人

Answer 1

在这一行

myoleDataAdapter.Fill(mydataSet)

您尝试填充数据集，但此数据集从未初始化。

按照实际模式，您应该更改以这种方式初始化dataadapter的代码

Public Function GetMyoleDataAdapterStudentQuestionRepeat(ByVal topicId As String, ByVal groupId As String) As OleDbDataAdapter
    Try
        Dim strAccessConn As String = _appConfigDbConn
        Dim cn As OleDbConnection = New OleDbConnection(strAccessConn)
        Dim ds As New DataSet
        Dim da As New OleDbDataAdapter("qryStudentNameRandomBasedOnScore", cn)
        da.SelectCommand.CommandType = CommandType.StoredProcedure
        da.SelectCommand.Parameters.AddWithValue("@GroupID", groupId)
        Return da
    Catch ex As Exception
        Throw New ApplicationException(ex.InnerException.Message.ToString())
    End Try
        End Function

然后在调用者代码中写

 Dim myoleDataAdapter As OleDbDataAdapter = GroupData.GetMyoleDataAdapterStudentQuestionRepeat( topicId, groupId)
 mydataSet = new DataSet()
 myoleDataAdapter.Fill(mydataSet)
 ....

在返回适配器的方法中，您不需要传递数据集，因为您不以任何方式使用它，也不需要创建和填充其他数据集。只需返回适配器并处理调用者代码

当然，您也可以更改方法并返回填充了数据的数据集，而不是DataAdapter。可能这个解决方案可能被认为是封装的

Public Function GetStudentQuestionRepeat(ByVal topicId As String, ByVal groupId As String) _
                As Dataset
    ....
    Dim da As New OleDbDataAdapter("qryStudentNameRandomBasedOnScore", cn)
    da.SelectCommand.CommandType = CommandType.StoredProcedure
    da.SelectCommand.Parameters.AddWithValue("@GroupID", groupId)
    Dim ds = new Dataset()
    da.Fill(ds, "Student")
    Return ds
    ....        
End Function

顺便说一下，topidID变量传递和从未使用过的目的是什么？

Answer 2

为什么不返回Dataset而不是DataAdapter，例如：

    Public Function GetMyoleDataAdapterStudentQuestionRepeat(ByVal topicId As String, ByVal groupId As String) As DataSet
        Try
            Dim strAccessConn As String = _appConfigDbConn
            Dim cn As OleDbConnection = New OleDbConnection(strAccessConn)
            Dim ds As New DataSet
            Dim da As New OleDbDataAdapter("qryStudentNameRandomBasedOnScore", cn)
            da.SelectCommand.CommandType = CommandType.StoredProcedure
            da.SelectCommand.Parameters.AddWithValue("@GroupID", groupId)
            da.Fill(ds, "Student")
            Return ds
        Catch ex As Exception
            Throw New ApplicationException(ex.InnerException.Message.ToString())
        End Try
    End Function

然后当你打电话时会更短：

  Dim myDataSet As DataSet = GroupData.GetMyoleDataAdapterStudentQuestionRepeat(topicId, groupId)

  txtStudentName.DataBindings.Add("Text", myDataSet.Tables(0), "studentname")

使用VB.NET 2008从Access 2010视图检索数据会引发错误

2 个答案: