我正在制作一个程序，允许用户查看歌曲信息、播放其中的片段并购买选定的歌曲。
并允许用户点击购买按钮购买指定的曲子。
退房时：
如果用户没有购买任何曲子，他们将无法结帐，但他们可以退出程序。
使用 InputBox 以便用户可以输入他们的销售税率。由于用户正在输入一个值，因此您必须对他们的输入执行数据验证。
允许用户通过单击 InputBox Cancel 按钮取消签出过程。
当输入框显示时，文本框应该有焦点，当添加了错误的税值时，错误的值应该被清除，文本框应该重新获得焦点。
使用 Write/Writeline 创建一个名为 PurchaseOrder.txt 的采购订单文本文件，其中包括文件的创建日期和采购清单、小计、税收和总计。
当我单击所选歌曲的“购买”按钮并单击“结帐”按钮时，我得到一个输入框，输入数值，但是，它继续一遍又一遍地循环。我不明白为什么会这样。请参考下面代码中的 cmdCheckOut_Click 子例程。我认为这就是我得到错误的地方。
这是代码：
Public Structure musicInfo
<VBFixedString(30)> Public title As String
<VBFixedString(20)> Public artist As String
<VBFixedString(20)> Public genre As String
<VBFixedString(10)> Public duration As String
Public year As Integer
Public price As Double
<VBFixedString(15)> Public songFileName As String
End Structure
Public Const NoOfTunes = 5
Public songs(NoOfTunes - 1) As musicInfo
Option Explicit On
Imports System.IO
Public Class frmTunes
Public index As Integer
Public purchaseCount As Integer
Public purchasePrice(10) As Decimal
Public purchaseTitle(10) As String
Dim decimal1 As Decimal
Dim decimal3 As Decimal
Dim decimal4 As Decimal
Private Sub frmTunes_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
Dim i As Integer
FileOpen(1, "music.dat", OpenMode.Random, , , Len(songs(0)))
For i = 0 To NoOfTunes - 1
FileGet(1, songs(i))
Next
FileClose(1)
cmdPrevious.Visible = False
DisplaySong(0)
End Sub
Sub DisplaySong(ByVal i As Int32)
lblTitle.Text = songs(i).title
lblArtist.Text = songs(i).artist
lblGenre.Text = songs(i).genre
lblDuration.Text = songs(i).duration
lblYear.Text = Convert.ToString(songs(i).year)
lblPrice.Text = Convert.ToString(songs(i).price)
End Sub
Private Sub cmdStop_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles cmdStop.Click
My.Computer.Audio.Stop()
End Sub
Private Sub cmdPurchase_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles cmdPurchase.Click
purchaseTitle(purchaseCount) = lblTitle.Text
purchasePrice(purchaseCount) = Convert.ToDecimal(lblPrice.Text)
purchaseCount = (purchaseCount + 1)
End Sub
Private Sub cmdPrevious_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles cmdPrevious.Click
index = (index - 1)
If (index < 4) Then
cmdNext.Visible = True
End If
If (index = 0) Then
cmdPrevious.Visible = False
End If
DisplaySong(index)
End Sub
Private Sub cmdNext_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles cmdNext.Click
index = (index + 1)
If (index = NoOfTunes - 1) Then
cmdNext.Visible = False
End If
If (index > 0) Then
cmdPrevious.Visible = True
End If
DisplaySong(index)
End Sub
Private Sub cmdPlay_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles cmdPlay.Click
My.Computer.Audio.Play(songs(index).songFileName)
End Sub
Private Sub cmdCheckOut_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles cmdCheckOut.Click
Dim str1 As String = ""
If (purchaseCount = 0) Then
MsgBox("You have not ordered any items!", MsgBoxStyle.Exclamation, "Order Error")
Else
Do Until ((IsNumeric(str1) And (Decimal.Compare(decimal3, Decimal.Zero) <= 10)) And (Decimal.Compare(decimal3, (10D)) >= 0))
str1 = InputBox("Enter your tax rate as a %" & vbCrLf & "between and including 0 - 10:", "Tax Rate", "", -1, -1)
If (str1 <> "") Then
If (Not IsNumeric(str1)) Then
MsgBox("You must enter a numeric tax rate", MsgBoxStyle.Exclamation, "Tax Rate Error")
Else
Dim decimal3 As Decimal = Convert.ToDecimal(str1)
If ((Decimal.Compare(decimal3, Decimal.Zero) < 0) Or (Decimal.Compare(decimal3, (10D)) > 0)) Then
MsgBox("You must enter a tax rate between and including 0% - 10%", MsgBoxStyle.Exclamation, "Tax Rate Error")
End If
End If
End If
Loop
Dim StreamWriter As StreamWriter = File.CreateText("PurchaseOrder.txt")
StreamWriter.WriteLine("For Purchases dated: " & DateTime.Now.ToLongDateString())
StreamWriter.WriteLine()
Dim num2 As Integer = (purchaseCount - 1)
Dim num1 As Integer = 0
Do While (num1 <= num2)
StreamWriter.Write(Strings.FormatCurrency(CType(Me.purchasePrice(num1), Decimal) & " "))
StreamWriter.WriteLine(purchaseTitle(num1))
Dim decimal1 As Decimal = Decimal.Add(Nothing, purchasePrice(num1))
num1 = (num1 + 1)
Loop
StreamWriter.WriteLine("------")
StreamWriter.WriteLine(Strings.FormatCurrency(CType(decimal1, Decimal)) & " Subtotal")
Dim decimal2 As Decimal = New Decimal(((Convert.ToDouble(decimal3) * 0.01) * Convert.ToDouble(decimal1)))
StreamWriter.WriteLine(Strings.FormatCurrency(CType(decimal2, Decimal)) & " Tax")
StreamWriter.WriteLine("------")
Dim decimal4 As Decimal = Decimal.Add(decimal1, decimal2)
StreamWriter.WriteLine(Strings.FormatCurrency(CType(decimal4, Decimal)) & " Total")
MsgBox("Purchase Order has been created", MsgBoxStyle.OkOnly)
StreamWriter.Close()
Me.Close()
End If
End Sub
End Class