通用功能與絃樂

Question

什麼是處理這種情況的最好辦法特例：

我有這樣的泛型函數在字段值爲空，T爲字符串的特殊情況

Function FieldValue(Of T)(row As DataRow,fieldName As String) As T 
    Return If(row.IsNull(fieldName),Nothing,CType(row(fieldName),T)) 
End Function 

，我想返回String.Empty而不是Nothing。

Answer 1

我認爲最簡單的方法是爲T =串中的某個函數：

Function FieldValue(row As DataRow ,fieldName As String) As String 
    Return If(row.IsNull(fieldName), String.Empty, CType(row(fieldName), String)) 
End Function 

（在現有的通用功能的頂部）

---

這裏的另一種選擇：

Function FieldValue(Of T)(row As DataRow,fieldName As String) As T 
    If GetType(T) = GetType(String) And row.IsNull(fieldName) Then 
     Return CType(CType(String.Empty, Object), T) 
    Else 
     Return If(row.IsNull(fieldName), Nothing, CType(row(fieldName), T)) 
    End If 
End Function