屏蔽的文本框導致VB.NET錯誤

Question

在我的代碼中使用maskedtextbox時，它返回一個異常：

從字符串“”到類型“日期”的轉換無效

我的代碼是：

Dim msg, first, second As String
Dim firstdate, seconddate As Date
first = MaskedTextBox1.Text
second = MaskedTextBox2.Text
firstdate = CDate(first)
seconddate = CDate(second)
msg = "Days from today: " & DateDiff(DateInterval.Month, firstdate, seconddate)
MsgBox(msg)

但是，如果使用文本框代替maskedtextbox，我的代碼可以正常工作：

Dim msg, first, second As String
Dim firstdate, seconddate As Date
first = TextBox3.Text
second = TextBox4.Text
firstdate = CDate(first)
seconddate = CDate(second)
msg = "Days from today: " & DateDiff(DateInterval.Month, firstdate, seconddate)
MsgBox(msg)

Answer 1

最好使用一種解析方法來驗證日期信息：

If DateTime.TryParse(first, firstdate) AndAlso _
   DateTime.TryParse(second, seconddate) Then
  msg = "Days from today: " & DateDiff(DateInterval.Day, firstdate, seconddate)
  MessageBox.Show(msg)
Else
  MessageBox.Show("Invalid dates entered.")
End If