C＃DLL不能从VB6应用程序的影响按引用传递的一些值 [英] C# DLL cannot affect value of a number passed by reference from a VB6 application

问题描述

我有一个调用DLL VB6的传统VB6应用程序，我想端口VB6 DLL到C＃还没有触及的主要VB6应用code。旧的VB6的DLL不得不通过参考接收到VB6的长（32位整数）的一个接口，并更新该值。在我写的C＃DLL，更新后的值永远不会由主VB6应用程序可见。它充当虽然什么真正编组到C＃的DLL是对原始数据的一个副本，而不是对原始数据的基准的参考。我可以参考顺利通过阵列，并更新他们，但单值不行为。

C＃的DLL code看起来是这样的：

  [标记有​​ComVisible特性（真）]
公共接口IInteropDLL
{
   无效增量（REF的Int32 NUM）;
}
[标记有ComVisible特性（真）
公共类InteropDLL：IInteropDLL
{
    公共无效增量（REF的Int32 NUM）{NUM ++; }
}
 

调用VB6 code看起来是这样的：

 私人DLL作为IInteropDLL
私人小组的Form_Load（）
    设置DLL =新InteropDLL
结束小组
私人小组TestLongReference（）
    昏暗NUM只要
    NUM = 1
    dll.Increment（NUM）
    Debug.Print NUM打印1，而不是2.为什么？
结束小组
 

我是什么做错了吗？我会怎么做才能解决这个问题？
先谢谢了。

解决方案

  dll.Increment（NUM）
 

由于您使用括号，该值被强制按值传递的，而不是由引用（编译器创建一个临时的复制和传递的是的引用）。

删除括号：

  dll.Increment NUM
 

---

编辑：通过的 =htt​​p://stackoverflow.com/users/15639 / markj> markJ 。

I have a legacy VB6 application that calls a VB6 DLL, and I am trying to port the VB6 DLL to C# without yet touching the main VB6 application code. The old VB6 DLL had one interface that received a VB6 long (32-bit integer) by reference, and updated the value. In the C# DLL I have written, the updated value is never seen by the main VB6 application. It acts as though what was really marshalled to the C# DLL was a reference to a copy of the original data, not a reference to the original data. I can successfully pass arrays by reference, and update them, but single values aren't behaving.

The C# DLL code looks something like this:

[ComVisible(true)]
public interface IInteropDLL
{
   void Increment(ref Int32 num);
}
[ComVisible(true)]
public class InteropDLL : IInteropDLL
{
    public void Increment(ref Int32 num) { num++; }
}

The calling VB6 code looks something like this:

Private dll As IInteropDLL
Private Sub Form_Load()
    Set dll = New InteropDLL
End Sub
Private Sub TestLongReference()
    Dim num As Long
    num = 1
    dll.Increment( num )
    Debug.Print num      ' prints 1, not 2.  Why?
End Sub

What am I doing wrong? What would I have to do to fix it? Thanks in advance.

解决方案

dll.Increment( num )

Because you are using parentheses, the value is forcibly passed by value, not by reference (the compiler creates a temporary copy and passes that by reference).

Remove the parentheses:

dll.Increment num

---

EDIT: A more complete explanation by MarkJ.

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