为什么我的读者陷入无限循环[关闭]

Question

谁能解释一下为什么会陷入无限循环？我把它放在一个按钮下，效果很好。但是当我把它放在一个类中并实例化这个类时，它就会陷入无限循环。我认为它卡在循环中，因为当我添加断点时，它不会比循环内部更进一步。它甚至没有通过“End While”，但是如果我将此代码放在 ASP.NET 中的按钮单击下，它就可以正常工作。我究竟做错了什么？

请不要批评我向数据库传递值的方式是“SQL 注入”，因为这不会成为公开的事情，我很清楚这一点。

Imports System.Data
Imports System.Data.SqlClient


    'Step 1: Select the device ID
    Function SelectDevice(d As String, b As String, m As String, o As String) As String

        ' Try

        'Connect to database
        Dim xcitoDBConnection As SqlConnection
        xcitoDBConnection = New SqlConnection("Data Source=NOTDISPLAYED;" + "Initial Catalog=NOTDISPLAYED;" + "Integrated Security=True")
        Dim GetDeviceID As String = "SELECT DISTINCT(Identifier) FROM Support.Devices WHERE DeviceType='" & d & "' AND Brand = '" & b & "' AND Model = '" & m & "' AND OS = '" & o & "'"
        Dim command As SqlCommand = New SqlCommand(GetDeviceID, xcitoDBConnection)

        xcitoDBConnection.Open()
        'command.ExecuteScalar()

        Dim reader As SqlDataReader
        reader = command.ExecuteReader(CommandBehavior.CloseConnection)
        Dim GetID As String

        While reader.Read()
            GetID = reader("Identifier").ToString
            Return GetID
        End While

        xcitoDBConnection.Close()

        ' Catch ex As ApplicationException
        '  ex.Source = ("Selection Error")
        ' Throw ex

        ' Finally

        'End Try
    End Function
End Class

Answer 1

写

reader = command.ExecuteReader()

而不是

reader = command.ExecuteReader(CommandBehavior.CloseConnection)

因为您在返回前关闭了连接。 并返回函数结束

关注这个

Public Sub CreateCommand(ByVal queryString As String, _
  ByVal connectionString As String)
  Dim GetID As String

    Using connection As New SqlConnection(connectionString)
        connection.Open()

        Dim command As New SqlCommand(queryString, connection)
        Dim reader As SqlDataReader = command.ExecuteReader()
        While reader.Read()
            GetID = reader(0).ToString
        End While 
    End Using
    Return GetID 
End Sub