vb.net - 如何在 VB.net(使用结构类型)中从 VB6 重写 "LSet"？

Question

我有一个 VB6 应用程序，它使用 LSet() 和两种用户定义的数据类型 (Type)，将数据从一种类型分配给另一种类型，例如:

Lset type1 = Type2

现在我必须在 VB.net 中应用等效逻辑。但是，在 VB.net 中，LSet cannot be used against different types (在 VB6 中键入)。

如何在 VB.net 中实现 VB6 LSet 逻辑？

示例/典型代码:

Public MQ_Policy As typPolicyDataRetrieval 
Public typPolicyDataBlock As gtypPolicyDataBlock 

With MQ_Policy.Input 
   .PcPolicyIDNum = Mid(InputString, 1, 8) 
   .PcPolicyIDNumPrefix = " " 
   .Datalength = Format$(CLng(Len(MQ_Policy)) - (Len(MQ_Policy.MQHeader) + Len(MQ_Policy.Input.Datalength)), String$(Len(.Datalength), "0")) 
End With 

LSet typPolicyDataBlock = MQ_Policy

感谢您的所有帮助。

Answer 1

你不应该在 VB.NET 中这样做。
还有其他方法，比如定义从一种类型到另一种类型的转换运算符，然后在代码中使用它们:

Private Structure t1
    Public a As Short
    Public b As Short
End Structure

Private Structure t2
    Public v As Integer

    Public Shared Widening Operator CType(ByVal v As t1) As t2
        Return New t2 With {.v = v.a Or (CType(v.b, Integer) << 16)}
    End Operator
End Structure

Sub Main()
    Dim v1 As t1, v2 As t2

    v2 = v1 ' Works!
End Sub

但是，如果您非常确定应该执行按字节复制，并且您知道 alignment issues并且对他们感到满意，那么您可以这样做:

Imports System.Runtime.InteropServices

Public Function CopyStructure(ByVal s As Object, ByVal ResultType As System.Type) As Object
    Dim h As GCHandle

    Try
        h = GCHandle.Alloc(s, GCHandleType.Pinned)

        Return Marshal.PtrToStructure(h.AddrOfPinnedObject, ResultType)
    Finally
        If h.IsAllocated Then h.Free()
    End Try
End Function

Sub Main()
    Dim v1 As t1, v2 As t2

    v2 = DirectCast(CopyStructure(v1, GetType(t2)), t2)
End Sub