阅读器关闭时调用 Read 的尝试无效。 VB.net答案

【问题标题】：Invalid attempt to call Read when reader is closed. vb.net阅读器关闭时调用 Read 的尝试无效。 VB.net
【发布时间】：2014-08-14 07:33:44
【问题描述】：

我的 WinForm 中有这个子：

Public Function CheckSentToday(ByVal date1 As DateTime) As Boolean
    Dim cmSql As New SqlCommand("Check_Today", cnSql)
    Try
        cmSql.CommandType = CommandType.StoredProcedure
        cmSql.Parameters.AddWithValue("@date1", String.Format("{0:yyyy-MM-dd}", date1))
        If Not cnSql Is Nothing AndAlso cnSql.State = ConnectionState.Closed Then cnSql.Open()
        If cmSql.ExecuteScalar IsNot Nothing Then
            Return True
        Else
            Return False
        End If
    Catch ex As Exception
        WriteToText("CheckSentToday", ex.ToString)
        CheckSentToday = False
    Finally
        If Not cnSql Is Nothing AndAlso cnSql.State = ConnectionState.Open Then cnSql.Close()
    End Try

End Function

我在执行SqlCommand之前打开连接，

并在finally 子句中关闭连接

不过，每次调用这个 sub 时它都会返回以下错误：

Description:System.InvalidOperationException: Invalid attempt to call Read when reader is closed.
   at System.Data.SqlClient.SqlDataReader.ReadInternal(Boolean setTimeout)
   at System.Data.SqlClient.SqlDataReader.Read()
   at System.Data.SqlClient.SqlCommand.CompleteExecuteScalar(SqlDataReader ds, Boolean returnSqlValue)
   at System.Data.SqlClient.SqlCommand.ExecuteScalar()

谁能帮我找出原因？

任何帮助将不胜感激

【问题讨论】：

标签： vb.net ado.net sqlconnection sqlcommand

【解决方案1】：

改用Using-statement，不要重复使用SqlConnection：

Public Function CheckSentToday(ByVal date1 As DateTime) As Boolean
    Using cnSql = New SqlConnection("connection-string")
        Using cmSql As New SqlCommand("Check_Today", cnSql)
            cmSql.CommandType = CommandType.StoredProcedure
            cmSql.Parameters.AddWithValue("@date1", String.Format("{0:yyyy-MM-dd}", date1))
            Try
                cnSql.Open()
                If cmSql.ExecuteScalar IsNot Nothing Then
                    Return True
                Else
                    Return False
                End If
            Catch ex As Exception
                WriteToText("CheckSentToday: ", ex.ToString)
                CheckSentToday = False
            End Try
        End Using
    End Using
End Function

【讨论】：