1

我有一个功能如下:

Function foo(ByVal c As CustomType, ByValue str as String) As Object
   Dim o as Object
   Select Case c.TypeName
     Case "System.String"
       If str = String.Empty Then
         o = DBNull.Value
       Else
         o = value
       End If
     Case "System.Int64"
       Try
         o = Long.Parse(value, Globalization.NumberStyles.Any)
       Catch
         o = DBNull.Value
       End Try
     Case "System.Double"
       Try
         o = Double.Parse(value, Globalization.NumberStyles.Any)
       Catch
         o = DBNull.Value
       End Try
     Case "System.Int32"
       Try
         o = Int32.Parse(value, Globalization.NumberStyles.Any)
       Catch
         o = DBNull.Value
       End Try
     Case "System.DateTime"
       Try
         o = DateTime.Parse(value)
       Catch
         o = DBNull.Value
       End Try
   Return o
End Function

这个功能让我想写一个通用版本。由于像 C++ 这样的 .NET 中不允许部分专业化(如果我在这里错了,请纠正我),我可以通过哪些方式使用泛型的任何特性。我做了一个尴尬的尝试,但失败了:

Function foo(Of T)(...) as Object
  Dim o As Object
  Try
     o = T.Parse(...) 'This doesnt work
  Catch
     o = DBNull.Value  
  End Try  
  ...
End Function
'Add functions for handling String and DateTime maybe?
4

2 回答 2

3

确实,您不能使用T.whatever泛型;只能采用(基于 的已知约束)的实例方法。TT

也许是这样的:

// return object since SQL parameter packing
static object Parse<T>(string value)
{
    if (string.IsNullOrEmpty(value)) return DBNull.Value; // for SQL parameter
    return TypeDescriptor.GetConverter(typeof(T)).ConvertFromString(value);
}

?

于 2012-05-02T05:40:48.977 回答
1

您可以使用反射以某种方式简化代码:

If c.Type.Primitive Then
   o = c.Type.GetMethod("Parse").Invoke(Nothing, New Object() {value, Globalization.NumberStyles.Any}) 
于 2012-05-02T05:50:51.350 回答