Question

我正在为课程作业创建座位预订计划，用户可以选择他/她希望预订座位的行，然后是他们希望预订的座位数。

Public Class Form1

Private Sub ListBox2_SelectedIndexChanged(sender As Object, e As EventArgs) Handles ListBox2.SelectedIndexChanged

End Sub

Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click

    Dim rowNumber As Integer
    Dim SeatsData As String(,) = {{"booked", "A2", "A3", "A4", "A5", "A6", "A7", "A8", "A9", "A10"}, {"booked", "booked", "booked", "booked", "booked", "booked", "booked", "booked", "booked", "booked"}, {"C1", "C2", "C3", "C4", "C5", "C6", "C7", "C8", "C9", "C10"}, {"D1", "booked", "booked", "D4", "D5", "D6", "D7", "D8", "D9", "D10"}, {"E1", "E2", "booked", "booked", "booked", "E6", "E7", "E8", "E9", "E10"}}

    If ListBox2.Text = "A" Then
        rowNumber = 0
    ElseIf ListBox2.Text = "B" Then
        rowNumber = 1
    ElseIf ListBox2.Text = "C" Then
        rowNumber = 2
    ElseIf ListBox2.Text = "D" Then
        rowNumber = 3
    ElseIf ListBox2.Text = "E" Then
        rowNumber = 4
    End If

    FindSeats(rowNumber, ListBox1.Text, SeatsData)

End Sub
Function FindSeats(ByVal RowNumber As Integer, ByVal NumSeats As Integer, SeatsData As Array) As String

    Dim i As Integer = 0
    Dim arrayPos As Integer = 0
    Dim largestStreak As Integer = 0
    Dim FirstSeat As String = 0
    Dim LastSeat As String = 0
    Dim foundSeats As Boolean = False
    Dim returnMsg As String = ""

    Do While foundSeats = False
        Dim seatChar As String = SeatsData(RowNumber, arrayPos)
        arrayPos = arrayPos + 1

        If seatChar = "booked" Then
            i = 0
        Else
            If i = 0 Then
                FirstSeat = seatChar
            End If
            i = i + 1

            If i > largestStreak Then
                largestStreak = i
            End If

        End If

        If i = NumSeats Then
            LastSeat = seatChar
            If FirstSeat = LastSeat Then
                returnMsg = "Found seat: " + FirstSeat
            Else
                returnMsg = "Found seats: " + FirstSeat + " - " + LastSeat
            End If
            MsgBox(returnMsg)
            Label3.Text = returnMsg
            foundSeats = True
            Exit Do
        End If

        If arrayPos = 10 Then
            returnMsg = "Not enough available seats, maximum available seats: " + CStr(largestStreak)
            MsgBox(returnMsg)
            Label3.Text = returnMsg
            Exit Do
        End If
    Loop
End Function
End Class

我遇到的问题是当用户选择他们想要的座位数而不是他们想要的那一行时，该程序会自动预订A行中的座位。如何解决这个问题？此外，当用户选择一行而不是多个席位（反之亦然）时，表单将转到代码并输出以下错误消息：＆＃34;未处理的类型＆＃39; System.InvalidCastException＆＃39;发生在Microsoft.VisualBasic.dll

其他信息：从字符串转换＆＃34;＆＃34;输入＆＃39;整数＆＃39;无效。＆＃34;

如何解决这些错误？我是VB的新手，所以如果有任何明显的话，那么我道歉！

Answer 1

你得到例外是因为你这样叫FindSeats：

FindSeats(rowNumber, ListBox1.Text, SeatsData)

请注意FindSeats的签名实际上是

Function FindSeats(RowNumber As Integer, NumSeats As Integer, SeatsData As Array) As String

因此，您将ListBox1.Text字符串作为NumSeats参数传递，该参数为Integer。由于您使用Option Strict Off，VB.Net会尝试将ListBox1.Text中的字符串隐式转换为Integer。

如果ListBox1.Text为空，则会失败，这就是它告诉您的异常消息：

从字符串“”到“整数”类型的转换无效。

首先，将Option Strict转为On，然后您将看到所有那些在运行时会咬你的漂亮的隐式转换。继续使用有意义的安全显式转换替换它们。

在用户点击Button1而不选择ListBox1之前的内容时，请考虑如何处理此案例。

也许您想使用Int32.TryParse来处理此类情况，或者可能在ListBox1

中预选有效值

VB Seat预订文件输出错误

1 个答案: