.net - 创建将字符串转换为可为空的数字的通用方法

Question

我有3个相似的函数，它们仅根据数字类型而变化:

<Extension()> _
Public Function ToNullableShort(ByVal str As String) As Short?
    Dim intReturn As Short
    If Short.TryParse(str, intReturn) Then
        Return intReturn
    Else
        Return Nothing
    End If
End Function

<Extension()> _
Public Function ToNullableByte(ByVal str As String) As Byte?
    Dim intReturn As Byte
    If Byte.TryParse(str, intReturn) Then
        Return intReturn
    Else
        Return Nothing
    End If
End Function

<Extension()> _
Public Function ToNullableLong(ByVal str As String) As Long?
    Dim intReturn As Long
    If Long.TryParse(str, intReturn) Then
        Return intReturn
    Else
        Return Nothing
    End If
End Function

我试图以此做一个通用函数，但是做不到。我如何制作一个通用函数，该函数将接受一个特定的T并将其设为Nullable(T)？

Answer 1

这里有一个相同的问题(在C#中):Convert string to nullable type (int, double, etc...)

Public Function ConvertString(Of T As Structure)(ByVal value As String) As System.Nullable(Of T)
    Try
        Return DirectCast(Convert.ChangeType(value, GetType(T)), T)
    Catch
        Return Nothing
    End Try
End Function