错误值的消息框

Question

我正在做一个关于vb.net的项目，我必须确定一个月中的天数，以及给定的年份是否是闰年。所有的代码都已完成。所有我不能做的是一个消息框将出现的编码，如果月份是不正确的。

Dim year, days As Double
Dim leap As Boolean
Dim monthint As Integer
Dim monthstr As String

days = 0
leap = False

year = txtTheyear.Text
monthstr = txtThemonth.Text

If monthstr = "January" Then
    monthint = 1
    leap = Date.IsLeapYear(year)
    days = System.DateTime.DaysInMonth(year, monthint)

    Lstbx1.Items.Add(year)
    Lstbx1.Items.Add(leap)
    Lstbx1.Items.Add(days)
End If


If monthstr = "February" Then
    monthint = 2
    leap = Date.IsLeapYear(year)
    days = System.DateTime.DaysInMonth(year, monthint)

    Lstbx1.Items.Add(year)
    Lstbx1.Items.Add(leap)
    Lstbx1.Items.Add(days)
End If


If monthstr = "March" Then
    monthint = 3
    leap = Date.IsLeapYear(year)
    days = System.DateTime.DaysInMonth(year, monthint)

    Lstbx1.Items.Add(year)
    Lstbx1.Items.Add(leap)
    Lstbx1.Items.Add(days)
End If



If monthstr = "April" Then
    monthint = 4
    leap = Date.IsLeapYear(year)
    days = System.DateTime.DaysInMonth(year, monthint)

    Lstbx1.Items.Add(year)
    Lstbx1.Items.Add(leap)
    Lstbx1.Items.Add(days)
End If



If monthstr = "May" Then
    monthint = 5
    leap = Date.IsLeapYear(year)
    days = System.DateTime.DaysInMonth(year, monthint)

    Lstbx1.Items.Add(year)
    Lstbx1.Items.Add(leap)
    Lstbx1.Items.Add(days)
End If



If monthstr = "June" Then
    monthint = 6
    leap = Date.IsLeapYear(year)
    days = System.DateTime.DaysInMonth(year, monthint)

    Lstbx1.Items.Add(year)
    Lstbx1.Items.Add(leap)
    Lstbx1.Items.Add(days)
End If



If monthstr = "July" Then
    monthint = 7
    leap = Date.IsLeapYear(year)
    days = System.DateTime.DaysInMonth(year, monthint)

    Lstbx1.Items.Add(year)
    Lstbx1.Items.Add(leap)
    Lstbx1.Items.Add(days)
End If



If monthstr = "August" Then
    monthint = 8
    leap = Date.IsLeapYear(year)
    days = System.DateTime.DaysInMonth(year, monthint)

    Lstbx1.Items.Add(year)
    Lstbx1.Items.Add(leap)
    Lstbx1.Items.Add(days)
End If



If monthstr = "September" Then
    monthint = 9
    leap = Date.IsLeapYear(year)
    days = System.DateTime.DaysInMonth(year, monthint)

    Lstbx1.Items.Add(year)
    Lstbx1.Items.Add(leap)
    Lstbx1.Items.Add(days)
End If



If monthstr = "October" Then
    monthint = 10
    leap = Date.IsLeapYear(year)
    days = System.DateTime.DaysInMonth(year, monthint)

    Lstbx1.Items.Add(year)
    Lstbx1.Items.Add(leap)
    Lstbx1.Items.Add(days)
End If



If monthstr = "November" Then
    monthint = 11
    leap = Date.IsLeapYear(year)
    days = System.DateTime.DaysInMonth(year, monthint)

    Lstbx1.Items.Add(year)
    Lstbx1.Items.Add(leap)
    Lstbx1.Items.Add(days)
End If



If monthstr = "December" Then
    monthint = 12
    leap = Date.IsLeapYear(year)
    days = System.DateTime.DaysInMonth(year, monthint)

    Lstbx1.Items.Add(year)
    Lstbx1.Items.Add(leap)
    Lstbx1.Items.Add(days)

End If





With Lstbx1.Items
    .Clear()
    .Add("Year" & vbTab & vbTab & "Is it a leap year" & vbTab & "Month" & vbTab & "Number of days")
    .Add("----" & vbTab & vbTab & "-----------------" & vbTab & "-----" & vbTab & "--------------")
    .Add(txtTheyear.Text & vbTab & vbTab & leap & vbTab & vbTab & txtThemonth.Text & vbTab & days)
End With

为一个消息框尝试过的代码：

If monthstr= "January" or "February" ...
Then ...
Else MsgBox ("Type the month correctly")
End if

Answer 1

它需要是

If monthstr="January" or monthstr="February" ...

如果您想在这里使用IF，对于select，请参阅前面un-lucky提供答案

顺便说一句，你也可以用一种更短的方式(如果你想的话)来编写代码，只需使用下面这样的代码：

Private Sub btCreate_Click(sender As Object, e As RoutedEventArgs) Handles btStartButton.Click
    'replace constants with values from your textboxes
    Dim yearPart As String = "2010"
    Dim monthpart As String = "January"

    Dim dt As DateTime
    Try
        dt = DateTime.ParseExact("01 " + monthpart + " " + yearPart,
                                      "dd MMMM yyyy",
                                      Globalization.CultureInfo.InvariantCulture)
        'MsgBox(dt.Year & " " & dt.Month & " " & Date.IsLeapYear(dt.Year))
        Lstbx1.Items.Add(dt.Year)
        Lstbx1.Items.Add(Date.IsLeapYear(dt.Year)))
        Lstbx1.Items.Add(dt.Month)
    Catch ex As Exception
        MsgBox("Incorrect Entry..! Type the month correctly")
    End Try

End Sub

神奇之处在于MMMM短语中DateTime.ParseExact的第二个参数，因为这是一种表示月份的字面表示形式

Answer 2

整个场景的简化代码：

    Dim isSuccess As Boolean = True '<-- variable for checking whether the process completed successfully
    Lstbx1.Items().Clear()
    Select Case monthstr
        Case "January", "jan", "january"
            monthint = 1
        Case "February", "feb", "february"
            monthint = 2
        Case "March", "mar", "march"
            monthint = 3
            'Write cases for other months too
        Case "December", "dec", "december"
            monthint = 12
        Case Else
            MsgBox("Incorrect Entry..! Type the month correctly")
    End Select
    'No wdo the operation here;
    If Not isSuccess Then
        leap = Date.IsLeapYear(year)
        days = System.DateTime.DaysInMonth(year, monthint)
    End If
    ' Here you can populate the List

这样使用的好处：

• 可以通过使用select
• 避免检查多个条件用户可以为January输入三个条件中的任何一个(“1月”、“1月”、“1月”)之前它将只接受January区分大小写)。
• 根据您在问题中的请求；您可以在case else中显示一条自定义消息，如果所有其他条件均为假