.net - CType 和类型转换异常

Question

Public Property Duration() As Integer
Get
  Try
    Return CType(Item(DurationColumn), Integer)
  Catch e As Global.System.InvalidCastException
    Throw New Global.System.Data.StrongTypingException("The value for column 'Duration' in table 'T_MembershipSale' is DBNull.", e)
  End Try
End Get
Set(ByVal value As Integer)
  Item(DurationColumn) = value
End Set
End Property

当用户想要分配整数""时会发生什么？Item(DurationColumn)我得到一个例外。有什么干净的解决方案可以避免这种情况并设置0为""？

Answer 1

Use Int32.TryParse:

Dim number as Integer
If Not Int32.TryParse(DurationColumn, number) Then number = 0
return number

This handles the case of "", as well as any other invalid value (i.e. non-number) the user might enter.

Answer 2

看TryCast和Int32.TryParse。

Answer 3

您可以使用IsNumeric

    number = If(IsNumeric(DurationColumn), CType(DurationColumn, Integer), 0)

Answer 4

您可以先将函数返回分配给变量，然后在转换前检查变量。

    Dim sRet As String = Item(DurationColumn)
    If Not String.IsNullOrEmpty(sRet) Then Convert.ToInt32(sRet)