异常Unhandle System.IndexOutOfRangeException

Question

此代码是关于查看已发布的咨询时间表。不幸的是，我坚持使用if语句。错误发生在以下行：如果dr（“Lecturer”）= ComboBox2.SelectedItem则||我正在使用组合框来显示数据库中的数据，这意味着组合框中有一个项目列表，我将选择任何讲师，以便它显示在表单中。我有一个数据库，其中包含已发布的时间表，如图所示。并且存储在此处（数据库）的所有数据实际上都不可用（声明为red = unavailable，lime = available），除了可用的数据未存储到数据库中。所以，我现在正在做的是从数据库中读取并匹配“时间”，“可用”和“讲师”，并将其更改为（红色）到相应的标签中（用石灰色）。

Database

The Form

    Imports System.Data.OleDb
Public Class viewconsultationschedule
Dim time1 As String = "8.00am-10.00am"
Dim time2 As String = "10.00am-12.00pm"
Dim time3 As String = "12.00pm-2.00pm"
Dim time4 As String = "2.00pm-4.00pm"
Dim time5 As String = "4.00pm-6.00pm"
Dim day1 As String = "Monday"
Dim day2 As String = "Tuesday"
Dim day3 As String = "Wednesday"
Dim day4 As String = "Thursday"
Dim day5 As String = "Friday"

Dim conn = New OleDbConnection("Provider=Microsoft.ACE.OLEDB.12.0;Data Source=sdpdatabase.accdb;Persist Security Info=False;")
Dim cmd As OleDbCommand
Dim cmd2 As OleDbCommand
Dim dr As OleDbDataReader
Dim sql As String
Dim sql2 As String
Private Sub ToolStrip1_ItemClicked(sender As Object, e As ToolStripItemClickedEventArgs) Handles ToolStrip1.ItemClicked

End Sub

Private Sub ComboBox2_SelectedIndexChanged(sender As Object, e As EventArgs) Handles ComboBox2.SelectedIndexChanged
    'If (ComboBox2.SelectedIndex = 3) Then

    Dim time1 As String = "8.00am-10.00am"
        Dim time2 As String = "10.00am-12.00pm"
        Dim time3 As String = "12.00pm-2.00pm"
        Dim time4 As String = "2.00pm-4.00pm"
        Dim time5 As String = "4.00pm-6.00pm"
        Dim day1 As String = "Monday"
        Dim day2 As String = "Tuesday"
        Dim day3 As String = "Wednesday"
        Dim day4 As String = "Thursday"
        Dim day5 As String = "Friday"
        Dim conn = New OleDbConnection("Provider=Microsoft.ACE.OLEDB.12.0;Data Source=sdpdatabase.accdb;Persist Security Info=False;")
        sql = "Select * FROM consultationschedule WHERE Lecturer=@Lecturer" ' And [Time]=@Time AND weekDay=@weekDay "
        sql2 = "Select COUNT (*) FROM consultationschedule WHERE Lecturer=@lecturer"
        conn.Open()
        cmd = New OleDbCommand(sql, conn)
        cmd2 = New OleDbCommand(sql2, conn)

        cmd.Parameters.AddWithValue("@lecturer", ComboBox2.SelectedItem)
        'cmd.Parameters.AddWithValue("@[Time]", time1)
        'cmd.Parameters.AddWithValue("@weekDay", day1)

        cmd2.Parameters.AddWithValue("@lecturer", ComboBox2.SelectedItem)
        'cmd2.Parameters.AddWithValue("@[Time]", time2)
        'cmd2.Parameters.AddWithValue("@weekDay", day2)
        Dim count As Integer = cmd2.ExecuteScalar()

        dr = cmd.ExecuteReader
        dr = cmd2.ExecuteReader
        If (dr.HasRows) Then
        For i = 1 To count
            If (i = 1) Then
                dr.Read()

                If dr("Lecturer") = ComboBox2.SelectedItem Then

                    If dr("Available") = "1" Then
                        Label11.BackColor = Color.Red

                    Else
                        Label11.BackColor = Color.Lime
                    End If

                ElseIf (i = 2) Then
                    If dr("Lecturer") = ComboBox2.SelectedItem Then
                        If dr("Available") = "1" Then
                            Label12.BackColor = Color.Red

                        Else
                            Label12.BackColor = Color.Lime


                        End If


                    ElseIf (i = 3) Then
                        If dr("Lecturer") = ComboBox2.SelectedItem Then
                            If dr("Available") = "1" Then
                                Label13.BackColor = Color.Red

                            Else
                                Label13.BackColor = Color.Lime


                            End If



                        ElseIf (i = 4) Then
                            If dr("Lecturer") = ComboBox2.SelectedItem Then
                                If dr("Available") = "1" Then
                                    Label14.BackColor = Color.Red

                                Else
                                    Label14.BackColor = Color.Lime


                                End If

                            ElseIf (i = 5) Then
                                If dr("Lecturer") = ComboBox2.SelectedItem Then
                                    If dr("Available") = "1" Then
                                        Label15.BackColor = Color.Red

                                    Else
                                        Label15.BackColor = Color.Lime


                                    End If
                                ElseIf (i = 6) Then
                                    If dr("Lecturer") = ComboBox2.SelectedItem Then
                                        If dr("Available") = "1" Then
                                            Label16.BackColor = Color.Red

                                        Else
                                            Label16.BackColor = Color.Lime


                                        End If
                                    ElseIf (i = 7) Then
                                        If dr("Lecturer") = ComboBox2.SelectedItem Then
                                            If dr("Available") = "1" Then
                                                Label17.BackColor = Color.Red

                                            Else
                                                Label17.BackColor = Color.Lime


                                            End If
                                        ElseIf (i = 8) Then
                                            If dr("Lecturer") = ComboBox2.SelectedItem Then
                                                If dr("Available") = "1" Then
                                                    Label18.BackColor = Color.Red

                                                Else
                                                    Label18.BackColor = Color.Lime


                                                End If
                                            ElseIf (i = 9) Then
                                                If dr("Lecturer") = ComboBox2.SelectedItem Then
                                                    If dr("Available") = "1" Then
                                                        Label19.BackColor = Color.Red

                                                    Else
                                                        Label19.BackColor = Color.Lime


                                                    End If
                                                ElseIf (i = 10) Then
                                                    If dr("Lecturer") = ComboBox2.SelectedItem Then
                                                        If dr("Available") = "1" Then
                                                            Label20.BackColor = Color.Red

                                                        Else
                                                            Label20.BackColor = Color.Lime

                                                        End If
                                                    ElseIf (i = 11) Then
                                                        If dr("Lecturer") = ComboBox2.SelectedItem Then
                                                            If dr("Available") = "1" Then
                                                                Label21.BackColor = Color.Red

                                                            Else
                                                                Label21.BackColor = Color.Lime

                                                            End If
                                                        ElseIf (i = 12) Then
                                                            If dr("Lecturer") = ComboBox2.SelectedItem Then
                                                                If dr("Available") = "1" Then
                                                                    Label22.BackColor = Color.Red

                                                                Else
                                                                    Label22.BackColor = Color.Lime

                                                                End If
                                                            ElseIf (i = 13) Then
                                                                If dr("Lecturer") = ComboBox2.SelectedItem Then
                                                                    If dr("Available") = "1" Then
                                                                        Label23.BackColor = Color.Red

                                                                    Else
                                                                        Label23.BackColor = Color.Lime
                                                                    End If
                                                                ElseIf (i = 14) Then
                                                                    If dr("Lecturer") = ComboBox2.SelectedItem Then
                                                                        If dr("Available") = "1" Then
                                                                            Label24.BackColor = Color.Red

                                                                        Else
                                                                            Label24.BackColor = Color.Lime

                                                                        End If
                                                                    ElseIf (i = 15) Then
                                                                        If dr("Lecturer") = ComboBox2.SelectedItem Then
                                                                            If dr("Available") = "1" Then
                                                                                Label25.BackColor = Color.Red

                                                                            Else
                                                                                Label25.BackColor = Color.Lime

                                                                            End If
                                                                        ElseIf (i = 16) Then
                                                                            If dr("Lecturer") = ComboBox2.SelectedItem Then
                                                                                If dr("Available") = "1" Then
                                                                                    Label26.BackColor = Color.Red

                                                                                Else
                                                                                    Label26.BackColor = Color.Lime
                                                                                End If
                                                                            ElseIf (i = 17) Then
                                                                                If dr("Lecturer") = ComboBox2.SelectedItem Then
                                                                                    If dr("Available") = "1" Then
                                                                                        Label27.BackColor = Color.Red

                                                                                    Else
                                                                                        Label27.BackColor = Color.Lime
                                                                                    End If
                                                                                ElseIf (i = 18) Then
                                                                                    If dr("Lecturer") = ComboBox2.SelectedItem Then
                                                                                        If dr("Available") = "1" Then
                                                                                            Label28.BackColor = Color.Red

                                                                                        Else
                                                                                            Label28.BackColor = Color.Lime
                                                                                        End If
                                                                                    ElseIf (i = 19) Then
                                                                                        If dr("Lecturer") = ComboBox2.SelectedItem Then
                                                                                            If dr("Available") = "1" Then
                                                                                                Label29.BackColor = Color.Red

                                                                                            Else
                                                                                                Label29.BackColor = Color.Lime

                                                                                            End If

                                                                                        ElseIf (i = 20) Then
                                                                                            If dr("Lecturer") = ComboBox2.SelectedItem Then
                                                                                                If dr("Available") = "1" Then
                                                                                                    Label30.BackColor = Color.Red

                                                                                                Else
                                                                                                    Label30.BackColor = Color.Lime
                                                                                                End If
                                                                                            ElseIf (i = 21) Then
                                                                                                If dr("Lecturer") = ComboBox2.SelectedItem Then
                                                                                                    If dr("Available") = "1" Then
                                                                                                        Label33.BackColor = Color.Red

                                                                                                    Else
                                                                                                        Label33.BackColor = Color.Lime
                                                                                                    End If
                                                                                                ElseIf (i = 22) Then
                                                                                                    If dr("Lecturer") = ComboBox2.SelectedItem Then
                                                                                                        If dr("Available") = "1" Then
                                                                                                            Label34.BackColor = Color.Red

                                                                                                        Else
                                                                                                            Label34.BackColor = Color.Lime
                                                                                                        End If
                                                                                                    ElseIf (i = 23) Then
                                                                                                        If dr("Lecturer") = ComboBox2.SelectedItem Then
                                                                                                            If dr("Available") = "1" Then
                                                                                                                Label35.BackColor = Color.Red

                                                                                                            Else
                                                                                                                Label35.BackColor = Color.Lime
                                                                                                            End If
                                                                                                        ElseIf (i = 24) Then
                                                                                                            If dr("Lecturer") = ComboBox2.SelectedItem Then
                                                                                                                If dr("Available") = "1" Then
                                                                                                                    Label36.BackColor = Color.Red

                                                                                                                Else
                                                                                                                    Label36.BackColor = Color.Lime

                                                                                                                End If
                                                                                                            ElseIf (i = 25) Then
                                                                                                                If dr("Lecturer") = ComboBox2.SelectedItem Then
                                                                                                                    If dr("Available") = "1" Then
                                                                                                                        Label37.BackColor = Color.Red

                                                                                                                    Else
                                                                                                                        Label37.BackColor = Color.Lime

                                                                                                                    End If

                                                                                                                End If
                                                                                                            End If
                                                                                                        End If
                                                                                                    End If
                                                                                                End If
                                                                                            End If
                                                                                        End If
                                                                                    End If
                                                                                End If
                                                                            End If
                                                                        End If
                                                                    End If
                                                                End If
                                                            End If
                                                        End If
                                                    End If
                                                End If
                                            End If
                                        End If
                                    End If
                                End If
                            End If
                        End If
                    End If
                End If
            End If
        Next
    End If

Answer 1

您从第一个SQL命令中选择记录，然后立即丢弃它们并将其替换为第二个SQL命令的结果：

dr = cmd.ExecuteReader
dr = cmd2.ExecuteReader

第二个命令没有名为"Lecturer"的字段，它只是一个COUNT()值。

看起来你想要的只是完全删除这一行：

dr = cmd2.ExecuteReader

因为您已在上面执行cmd2并将该单个值存储在count变量中。

另请注意，您的循环不是必需的：

For i = 1 To count
    If (i = 1) Then
        '...
    End If
Next

这个循环在设计上只会迭代一次。因此，您首先不需要循环，只需根据需要执行一次代码。