我有几个建议。首先,为你在 COM 中接触的任何东西创建一个接口,即使它只是一个没有方法和只有属性的沼泽标准 DTO。COM 喜欢接口。它非常喜欢它们,以至于您在 COM 中触摸的所有东西都是一个界面。
另一个建议是您将 GuidAttribute 放置在您在 COM 中触摸的任何内容上。这将确保当您向 COM 注册托管程序集时,您的注册表不会出错。COM 喜欢 GUID 胜过喜欢接口,如果一个接口注册到多个 GUID,它很容易混淆,如果您没有在代码中硬修复接口 GUID,就会发生这种情况。具体的类也需要一个 GUIDAttribute。
我知道这很糟糕,但这就是为什么 MS 如此努力地让人们远离使用 COM。
话虽如此,您可能想要这样的 C#:
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Runtime.InteropServices;
namespace ClassLibrary1
{
[ComVisible(true)]
[Guid("1CEB24F2-BF13-417F-B5BC-DB8E82A56EAE")]
public interface ITestEntity1 //This is how TestEntity1 is visible to the COM code...so it needs a Guid.
{
bool Thing { get; set; }
}
[ComVisible(true)]
[Guid("C8B5A7C2-F67C-4271-A762-3642754F2233")]
public class TestEntity1 : ITestEntity1 //Created by the COM runtime...needs a Guid.
{
public bool Thing { get; set; }
}
[ComVisible(true)]
[Guid("8904A7EC-D865-4533-91EC-1F68524651D0")]
public interface ITestEntity2
{
string Description { get; set; }
}
[ComVisible(true)]
[Guid("668EE2E8-5A60-468B-8689-D9327090AA44")]
public class TestEntity2 : ITestEntity2
{
public string Description { get; set; }
}
[ComVisible(true)]
[Guid("2791082F-F505-49C4-8952-80C174E4FE96")]
public interface ITestGateway
{
//MarshalAsAttribute is somewhat important, it tells the tlbexp.exe tool to mark
// the comInputValue parameter as IUnknown* in the COM interface.
//This is good because VARIANTS kinda suck...You'll see what I mean in the C++
// side. It also keeps some jack-wagon from passing a VARIANT_BOOL in
// on your object parameter.
void DoSomething(string a, [MarshalAs(UnmanagedType.Interface)]object comInputValue);
}
[ComVisible(true)]
[Guid("C3D079F3-7869-4B3E-A742-263775C6EA63")]
public class TestGateway : ITestGateway
{
public void DoSomething(string a, object comInputValue)
{
if (a == "yes")
{
var entity = (TestEntity1)comInputValue;
}
else
{
var entity = (TestEntity2) comInputValue;
}
//OR
if(comInputValue is TestEntity1)
{
//Do whatever here, and you don't need to test
// a string input value.
}
else if(comInputValue is TestEntity2)
{
//Other stuff is done here.
}
else
{
//Error condition??
}
}
}
}
可以通过以下 C++ 调用:
// ComClient.cpp : Defines the entry point for the console application.
//
#include "stdafx.h"
#import <mscorlib.tlb> raw_interfaces_only
//This creates the CLSID_ and IID_ constants, and
// some strongly-typed interfaces.
#import "..\Debug\ClassLibrary1.tlb" no_namespace named_guids
int _tmain(int argc, _TCHAR* argv[])
{
ITestGateway* test = NULL;
char buffer[50];
gets(buffer); //Just a pause to attach the debugger in Managed + Native mode...hit enter in the console.
CoInitialize(NULL);
HRESULT hr = CoCreateInstance(CLSID_TestGateway,
NULL,
CLSCTX_INPROC_SERVER,
IID_ITestGateway,
reinterpret_cast<void**>(&test));
if(FAILED(hr)) {
printf("Couldn't create the instance!... 0x%x\n", hr);
gets(buffer);
} else {
_bstr_t someString("yes");
//Instead of fooling with CComVariant,
// just directly create a TestEntity1...which COM will return
// as an ITestEntity1.
ITestEntity1* testEntity1 = NULL;
HRESULT hr = CoCreateInstance(CLSID_TestEntity1,
NULL,
CLSCTX_INPROC_SERVER,
IID_ITestEntity1,
reinterpret_cast<void**>(&testEntity1));
if(FAILED(hr)) {
printf("Entity was not created!... 0x%x\n", hr);
gets(buffer);
return 0;
}
//Set some kind of property just for show.
testEntity1->PutThing(VARIANT_FALSE);
//If you attached your debugger with Managed code & Native code,
// you should be able to hit a C# break point during this call.
//Also, notice that there is no cast for testEntity1. All interfaces
// in COM derive from IUnknown, so you can just pass it.
//IDispatch also derives from IUnknown, so if that's what you already have,
// you can just pass it as well, with no cast.
test->DoSomething(someString, testEntity1);
printf("Something was done.");
testEntity1->Release(); //Release anything you make through CoCreateInstance()
}
test->Release();
return 0;
}