Question

以下是我的代码，我正在进行在线考试项目。当我点击下一步按钮时，问题会重复出现。

Imports System.Data.SqlClient
Partial Class Questions
    Inherits System.Web.UI.Page

    Dim cmd As New SqlCommand
    Dim Result As Integer = 0
    Dim Question_ID As Integer = Nothing
    Dim strconn As String = ConfigurationManager.ConnectionStrings("DefaultConnection").ConnectionString
    Dim con As New SqlConnection(strconn)

    Protected Sub rblQuestion_SelectedIndexChanged(sender As Object, e As EventArgs) Handles rblQuestion1.SelectedIndexChanged
        CheckAnswer(rblQuestion1.SelectedValue, lblQuestion1.Text)
    End Sub

    Private Sub CheckAnswer(ByVal Answer As String, ByVal Question As String)
        Dim RetrievedAnswer As String = Nothing

        Try
            Dim daQuestionID As New SqlDataAdapter("select Question_ID from tblQuestions where Question='" & Question & "'", con)
            Dim dsQuestionID As New Data.DataSet
            Dim dtQuestionID As New Data.DataTable

            If Not con.State = Data.ConnectionState.Open Then con.Open()
            daQuestionID.Fill(dsQuestionID)
            dtQuestionID = dsQuestionID.Tables(0)

            If Not dtQuestionID.Rows.Count <= 0 Then
                If Not IsDBNull(dtQuestionID.Rows(0).Item("Question_ID")) Then
                    Question_ID = dtQuestionID.Rows(0).Item("Question_ID")

                Else
                    Exit Sub
                End If
             End If
        Catch ex As Exception

        End Try

        Try
            Dim daAnswer As New SqlDataAdapter("select Answer from tblQuestions where Question_ID=" & Question_ID, con)
            Dim dsAnswer As New Data.DataSet
            Dim dtAnswer As New Data.DataTable

            If Not con.State = Data.ConnectionState.Open Then con.Open()
            daAnswer.Fill(dsAnswer)
            dtAnswer = dsAnswer.Tables(0)

            If Not dtAnswer.Rows.Count <= 0 Then
                If Not IsDBNull(dtAnswer.Rows(0).Item("Answer")) Then
                    RetrievedAnswer = dtAnswer.Rows(0).Item("Answer")
                End If
            End If

            If RetrievedAnswer = Answer Then
                Try
                    Dim sr As New IO.StreamReader(System.AppDomain.CurrentDomain.BaseDirectory & "\\result.txt")
                    Result = sr.ReadLine
                    sr.Close()
                    Result = Result + 1
                    Dim sw As New IO.StreamWriter(System.AppDomain.CurrentDomain.BaseDirectory & "\\result.txt")
                    sw.WriteLine(Result)
                    sw.Close()
                Catch ex As Exception

                End Try

            End If
        Catch ex As Exception

        End Try
    End Sub
    Protected Sub Page_Load(sender As Object, e As EventArgs) Handles Me.Load

        If Not IsPostBack Then
            Try
                Dim daQuestions As New SqlDataAdapter("SELECT TOP 20 * FROM tblQuestions ORDER BY NEWID()", con)
                Dim dsQuestions As New Data.DataSet
                Dim dtQuestions As New Data.DataTable

                If Not con.State = Data.ConnectionState.Open Then con.Open()
                daQuestions.Fill(dsQuestions)
                dtQuestions = dsQuestions.Tables(0)

                If Not dtQuestions.Rows.Count <= 0 Then
                    'For Question 1
                    If Not IsDBNull(dtQuestions.Rows(0).Item("Question")) Then
                        lblQuestion1.Text = dtQuestions.Rows(0).Item("Question")
                    End If
                    If Not IsDBNull(dtQuestions.Rows(0).Item("Option1")) Then
                        rblQuestion1.Items(0).Text = dtQuestions.Rows(0).Item("Option1")
                    End If
                    If Not IsDBNull(dtQuestions.Rows(0).Item("Option2")) Then
                        rblQuestion1.Items(1).Text = dtQuestions.Rows(0).Item("Option2")
                    End If
                    If Not IsDBNull(dtQuestions.Rows(0).Item("Option3")) Then
                        rblQuestion1.Items(2).Text = dtQuestions.Rows(0).Item("Option3")
                    End If
                    If Not IsDBNull(dtQuestions.Rows(0).Item("Option4")) Then
                        rblQuestion1.Items(3).Text = dtQuestions.Rows(0).Item("Option4")
                    End If
                End If
            Catch ex As Exception

            End Try

            'con.ConnectionString = ConfigurationManager.ConnectionStrings("DefaultConnection").ConnectionString
            cmd = New SqlCommand("insert into tblQuestions (Question, Option1, Option2, Option3, Option4,) values (@question, @option1, @option2, @option3, @option4)", con)
            cmd.Parameters.AddWithValue("@question", lblQuestion1.Text)
            cmd.Parameters.AddWithValue("@option1", rblQuestion1.Text)
            cmd.Parameters.AddWithValue("@option2", rblQuestion1.Text)
            cmd.Parameters.AddWithValue("@option3", rblQuestion1.Text)
            cmd.Parameters.AddWithValue("@option4", rblQuestion1.Text)
            'cmdInsertQuestion.Parameters.AddWithValue("@answer", txtAnswer.Text)
            Try
                con.Open()
                cmd.ExecuteNonQuery()
                con.Close()
                MsgBox(" ")
                'txtAnswer.Text = ""
                rblQuestion1.Text = ""
                rblQuestion1.Text = ""
                rblQuestion1.Text = ""
                rblQuestion1.Text = ""
            Catch ex As Exception
                'ex.Message
            End Try
        End If
    End Sub       

    Protected Sub rblQuestion1_SelectedIndexChanged(sender As Object, e As EventArgs) Handles rblQuestion1.SelectedIndexChanged

    End Sub

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

        If IsPostBack Then
            Try
                Dim daQuestions As New SqlDataAdapter("SELECT TOP 20 * FROM tblQuestions ORDER BY NEWID()", con)
                Dim dsQuestions As New Data.DataSet
                Dim dtQuestions As New Data.DataTable
                rblQuestion1.ClearSelection()
                If Not con.State = Data.ConnectionState.Open Then con.Open()
                daQuestions.Fill(dsQuestions)
                dtQuestions = dsQuestions.Tables(0)

                If Not dtQuestions.Rows.Count <= 0 Then

                    If Not IsDBNull(dtQuestions.Rows(0).Item("Question")) Then
                        lblQuestion1.Text = dtQuestions.Rows(0).Item("Question")
                    End If
                    If Not IsDBNull(dtQuestions.Rows(0).Item("Option1")) Then
                        rblQuestion1.Items(0).Text = dtQuestions.Rows(0).Item("Option1")
                    End If
                    If Not IsDBNull(dtQuestions.Rows(0).Item("Option2")) Then
                        rblQuestion1.Items(1).Text = dtQuestions.Rows(0).Item("Option2")
                    End If
                    If Not IsDBNull(dtQuestions.Rows(0).Item("Option3")) Then
                        rblQuestion1.Items(2).Text = dtQuestions.Rows(0).Item("Option3")
                    End If
                    If Not IsDBNull(dtQuestions.Rows(0).Item("Option4")) Then
                        rblQuestion1.Items(3).Text = dtQuestions.Rows(0).Item("Option4")
                    End If
                End If              

            Catch ex As Exception

            End Try

        End If
    End Sub

    Protected Sub btnSubmit_Click(sender As Object, e As EventArgs) Handles btnSubmit.Click
        Try
            Dim sr As New IO.StreamReader(System.AppDomain.CurrentDomain.BaseDirectory & "\\result.txt")
            Dim finalresult As Integer = sr.ReadLine
            sr.Close()
            Response.Write("<script type='text/javascript'>alert('Your Score is : " & finalresult & "');</script>")
            Dim sw As New IO.StreamWriter(System.AppDomain.CurrentDomain.BaseDirectory & "\\result.txt")
            sw.WriteLine(0)
            sw.Close()
        Catch ex As Exception

        End Try
    End Sub
End Class

Answer 1

对于初学者，您的Page_Load事件从tblQuestions中选择所有问题，然后将第一个问题放在屏幕上，然后将该行插入数据库，然后从屏幕中删除该值。每次加载页面时，该逻辑都保证会创建第一行的重复项。（因为插入命令）

猜测：我想您可能希望您的Insert查询进入button_click事件处理程序（可能是btnSubmit_Click）。

Answer 2

您可以通过使用for循环和每个循环轻松解决代码重复问题，同时只需递增整数变量。因为您的代码几乎相同。也许您应该考虑使用实体框架或LINQ to SQL，因为它确实有助于简化操作。最后不确定，但你真的需要一切可以为空。

Answer 3

我认为你对ASP.Net的运作方式存在误解。您尝试在Page_Load中进行一些初始化，就好像它在用户首次访问您的网页时运行一次而您不需要再次运行它。

每次用户在您的网页上发布任何回发到服务器的内容时，ASP.Net都会销毁您网页类中的所有数据，然后使用全新的网页课程启动您。

这就是它的工作原理。您将不得不完全重新考虑您的设计方式。

我如何避免在我的项目中重复数据

3 个答案: