无法为COM互操作包装器转换Marshal.GetActiveObject的结果 [英] Failed to cast result of Marshal.GetActiveObject for COM interop wrapper
问题描述
我正在努力研究如何访问C ++应用程序提供的COM接口并从C＃.NET应用程序中使用它。
I'm struggling to work out how to access a COM interface provided by a C++ application and use it from a C# .NET application.
我尝试访问我的C＃应用中的COM对象（由运行中的进程提供）是这样的：
I try to access my COM object (which is provided by a running process) from my C# app like this:
object obj = Marshal.GetActiveObject("MyLibrary.Application");
MyLibrary.IMainApp app = (MyLibrary.IMainApp)obj;
obj 的值不为空，但是当我尝试对其进行强制转换时，会得到 System.InvalidCastException 。
The value of obj is non-null, but when I try to cast it I get System.InvalidCastException.
我尝试实现自定义包装，并且链接到 TlbImp.exe 生成的DLL。两者都产生了相同的异常。
I tried implementing a custom wrapper and also linked against a DLL produced by TlbImp.exe. Both produced the same exception.
关于互操作的文档似乎很多，但这对我来说没有意义-主要是因为我不精通COM （我坚持维护其他人开发的代码），并通过深入研究进入C＃、. NET和WPF的可怕世界。
There seems to be a lot of documentation regarding interop, but it's not making sense to me -- mostly because I'm not COM-savvy (I am stuck maintaining code that someone else developed), and am entering the scary world of C#, .NET and WPF by diving headlong into it.
这就是我所拥有的在C ++端。...
Here's what I have on the C++ end....
IDL文件
实际上，扩展名是 .odl 。我不知道那是另一回事。请注意，我已经用 GUID-1 ， GUID-2 etc等占位符替换了GUID。 em> ...
Actually, the extension is .odl. I don't know if that's a different thing. Note that I've replaced the GUIDs with placeholders like GUID-1, GUID-2 etc...
import "oaidl.idl";
[ uuid(GUID-1), helpstring("My Type Library"), version(1.1) ]
library MyLibrary
{
importlib("stdole32.tlb");
// Primary dispatch interface for CMainApp
[ uuid(GUID-2) ]
dispinterface IMainApp
{
properties:
[id(1)] BOOL Mode;
methods:
[id(2)] void Quit();
[id(3)] void LogEventMessage(BSTR szMessageType, BSTR szMessage);
[id(4)] BOOL GetNoteDetails(BSTR szQualifiedName, BSTR* lpbstrOperator, DATE* lpdtDate);
};
// Class information for CMainApp
[ uuid(GUID-3) ]
coclass Application
{
[default] dispinterface IMainApp;
};
};
示例用法
当另一个C ++应用程序要调用函数（ eg Quit ）时，他们会这样做：
When another C++ application wants to call a function (eg Quit), they do this:
CLSID clsid;
HRESULT hr;
LPUNKNOWN lpUnk;
LPDISPATCH lpDisp;
BOOL bReturn = FALSE;
// Get Class ID
if (CLSIDFromProgID( OLESTR("MyLibrary.Application"), &clsid ) == S_OK )
{
// Get Active Object from ROT
if ( ( hr = GetActiveObject( clsid, NULL, &lpUnk ) ) == S_OK )
{
hr = lpUnk->QueryInterface( IID_IDispatch, (LPVOID*)&lpDisp );
lpUnk->Release();
if ( hr == S_OK )
{
CMainApp oMainApp;
oMainApp.AttachDispatch( lpDisp );
TRY
{
oMainApp.Quit();
bReturn = TRUE;
}
CATCH( CException, e )
{
bReturn = FALSE;
}
END_CATCH
}
}
}
类 CMainApp 似乎是由IDL编译器自动生成的。该文件被编译到要使用的项目中，并且基本上执行了许多 InvokeHelper 调用。我很高兴接受这只是它的工作方式，并且希望C＃不会引起混淆。
The class CMainApp seems to have been auto-generated by the IDL compiler. That file is compiled into the project that wants to use it, and basically does a whole lot of InvokeHelper calls. I'm happy enough to accept this is just the way it works, and I hope that C# is less convoluted.
试图用C＃包装 >
我遵循了C＃中有关COM互操作的MSDN指南。它建议我可以使用 TlbImp.exe ，但这引发了足够的警告让我失望了。此外，我不想分发另一个DLL。因此，我采用了另一种编写包装器的方法。
I followed an MSDN guide on COM interop in C#. It suggested I could use TlbImp.exe but that threw up enough warnings to put me off. Besides, I don't want to distribute another DLL. So I took the other approach of writing a wrapper.
这就是我写的：
using System.Runtime.InteropServices;
namespace MyLibrary
{
// Declare MainApp COM coclass
[ComImport, Guid("GUID-3")]
class MainApp
{
}
[Guid("GUID-2"), InterfaceType(ComInterfaceType.InterfaceIsDual)]
interface IMainApp
{
public void Quit();
public void LogEventMessage(
[In, MarshalAs(UnmanagedType.BStr)] string szMessageType,
[In, MarshalAs(UnmanagedType.BStr)] string szMessage );
public bool GetNoteDetails(
[In, MarshalAs(UnmanagedType.BStr)] string szQualifiedName,
[Out, MarshalAs(UnmanagedType.BStr)] out string lpbstrOperator );
out DateTime lpdtDate );
}
}
有人可以帮我理解吗？也许指出我犯了一个完全显而易见的愚蠢错误？ =）
Can someone gimme a hand to understand this? Perhaps point out a totally obvious stupid mistake that I've made? =)
推荐答案
您的示例C ++代码通过IDispatch使用 late-binding 。正确的做法是，您的COM服务器不支持早期绑定。您可以从IDL看出，它使用 dispinterface 而不是 interface 。
Your sample C++ code is using late-binding through IDispatch. Which is the correct way to do it, your COM server doesn't support early binding. You can tell from the IDL, it uses dispinterface instead of interface.
C＃中的等效方法是使用C＃ dynamic 关键字。像这样：
The equivalent way in C# is by using the C# dynamic keyword. Like this:
dynamic obj = Marshal.GetActiveObject("MyLibrary.Application");
obj.Quit();
这篇关于无法为COM互操作包装器转换Marshal.GetActiveObject的结果的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！
