“已经有一个与此连接关联的打开的数据读取器，必须首先将其关闭。”

晚上好，伙计们，您正在编写这段代码，但它告诉我我打开了一个 ExecuteReader。
你能帮我一下吗
谢谢

我尝试过的：

        Dim namecontr As String
        Dim rdr3 As Object

        Dim cmd3 As New MySqlCommand("Select s01_name_contr  from s01_tpcontratti where id=" & rdr.Item(2), cnnmysql)
        rdr3 = cmd3.ExecuteReader
        rdr3 = cmd3.ToString   ' 03/12 ore 17:25 capire perche non mi funziona si blocca 29/12 non ancora sbloccato
        'cmd3.Dispose()

        '  rdr3.Read()



        If rdr3.HasRows = True Then
            namecontr = rdr3.Item(0).ToString
        End If

        Dim data As Date = CDate(rdr.Item(3).ToString)
        grid_contratto.Rows.Add(rdr(0).ToString, rdr(2).ToString, namecontr, "stocazzo", data.ToShortDateString)
        '   rdr3.close()
    Loop
    rdr.Close()

    'cnnmysql.Clone()

End Sub

编辑 – “解决方案 1”中的 OP 代码和已删除的解决方案

Private Sub carica_grigliacontratti(id As String)
    '  Call connetti_mysql()
    ' cnnmysql.Open()

    If CInt("0" & id) = 0 Then Exit Sub
    Dim sql As String
    Dim rdr As Object
    ' Dim rdr2 As Object
    '  grspecialisti.Rows.Clear()


    sql = "Select * from a01_contratti where a01_cliente=" & id


    Dim cmd1 As New MySqlCommand(sql, cnnmysql)

    rdr = cmd1.ExecuteReader()
    cmd1.Dispose()


    If rdr.HasRows = False Then
        rdr.Close()

        Exit Sub
    End If
    sistema_grcerca()

    '    Dim perc As Long = 0
    '        Dim volte As Integer = 0w
    cnnmysql.Clone()
    grid_contratto.Rows.Clear()

    Do While rdr.Read

        Dim namecontr As String
        Dim rdr3 As Object

        Dim cmd3 As New MySqlCommand("Select s01_name_contr  from s01_tpcontratti where id=" & rdr.Item(2), cnnmysql)
        rdr3 = cmd3.ExecuteReader
        rdr3 = cmd3.ToString   ' 03/12 ore 17:25 capire perche non mi funziona si blocca 29/12 non ancora sbloccato
        'cmd3.Dispose()

        '  rdr3.Read()



        If rdr3.HasRows = True Then
            namecontr = rdr3.Item(0).ToString
        End If

        Dim data As Date = CDate(rdr.Item(3).ToString)
        grid_contratto.Rows.Add(rdr(0).ToString, rdr(2).ToString, namecontr, "stocazzo", data.ToShortDateString)
        '   rdr3.close()
    Loop
    rdr.Close()

    'cnnmysql.Clone()

End Sub

解决方案2

当您调用 ExecuteReader 时，它会“锁定”连接，因为读取器仅在您调用 Read 时才获取一行的信息。要释放锁，请关闭连接。处理这个问题的最佳方法是始终在 Using 堵塞[^]，然后在该块内的第二个 using 块中创建一个命令，并在其中的第三个块中创建一个读取器：

Using con As New SqlConnection(strConnect)
	con.Open()
	Using cmd As New SqlCommand("SELECT iD, description FROM myTable", con)
		Using reader As SqlDataReader = cmd.ExecuteReader()
			While reader.Read()
				Dim myId As Integer = CInt(reader("iD"))
				Dim myDesc As String = DirectCast(reader("description"), String)
				Console.WriteLine("ID: {0}" & vbLf & "    {1}", myId, myDesc)
			End While
		End Using
	End Using
End Using

当您的代码以任何方式退出Using块（例如Break、Return或Exception）时，其中创建的对象将自动关闭并为您处置，并且您永远不会遇到未关闭的读取器或连接的问题。