异步事件：已定义的链接器错误 [Windows Update API]

Question

好吧，我一直在摆弄一些 Microsoft Windows Update API，并尝试进行一些异步下载。使用 IDownloadProgressChangedCallback 接口的类的回调引用的 API 类 有关 API 的更多信息可以在此处找到。到目前为止我所做的只是瞎猜（我从来没有搞乱过回调或异步代码，或者微软的API）。我不断遇到“已定义”相同方法的问题。这是我到目前为止所拥有的：

main 方法中的相关代码：

IDownloadJob *_DownloadJob = NULL;
tagVARIANT NodeValue ; \\>>PS<< HOW DO I SET THIS TO A DEFUALT VALUE?
hr = _UpdateDownloader->BeginDownload(new DownloadProgressChangedCallback  ,new DownloadCompletedCallback, NodeValue,&_DownloadJob);

DownloadProgressChange.h:

#include <Wuapi.h>
#pragma once
class DownloadProgressChangedCallback  : public IDownloadProgressChangedCallback 
{
public:
    HRESULT STDMETHODCALLTYPE Invoke( IDownloadJob *downloadJob,  IDownloadProgressChangedCallbackArgs *callbackArgs);
    HRESULT STDMETHODCALLTYPE QueryInterface(  REFIID riid,  __RPC__deref_out void __RPC_FAR *__RPC_FAR *ppvObject);
    ULONG STDMETHODCALLTYPE AddRef( void) ;
    ULONG STDMETHODCALLTYPE Release( void);
};

DownloadProgressChange.cpp:

#include "StdAfx.h"
#include "DownloadProgressChange.h"
HRESULT STDMETHODCALLTYPE Invoke( IDownloadJob *downloadJob,  IDownloadProgressChangedCallbackArgs *callbackArgs)
{
    return NULL;
}

HRESULT STDMETHODCALLTYPE QueryInterface(  REFIID riid,  __RPC__deref_out void __RPC_FAR *__RPC_FAR *ppvObject)
{
    return NULL;
}

ULONG STDMETHODCALLTYPE AddRef( void) 
{
    return NULL;
}

ULONG STDMETHODCALLTYPE Release( void)
{
    return NULL;
}

DownloadCompletedCallback.h

#include <Wuapi.h>
#pragma once
class DownloadCompletedCallback  : public IDownloadCompletedCallback 
{
public:
    HRESULT STDMETHODCALLTYPE Invoke( IDownloadJob *searchJob,  IDownloadCompletedCallbackArgs *callbackArgs);
    HRESULT STDMETHODCALLTYPE QueryInterface(  REFIID riid,  __RPC__deref_out void __RPC_FAR *__RPC_FAR *ppvObject);
    ULONG STDMETHODCALLTYPE AddRef( void) ;
    ULONG STDMETHODCALLTYPE Release( void);
};

DownloadCompletedCallback.cpp

#include "StdAfx.h"
#include "DownloadCompletedCallback.h"
HRESULT STDMETHODCALLTYPE Invoke( IDownloadJob *searchJob,  IDownloadCompletedCallbackArgs *callbackArgs)
{
    return NULL;
}

HRESULT STDMETHODCALLTYPE QueryInterface(  REFIID riid,  __RPC__deref_out void __RPC_FAR *__RPC_FAR *ppvObject)
{
    return NULL;
}

ULONG STDMETHODCALLTYPE AddRef( void) 
{
    return NULL;
}

ULONG STDMETHODCALLTYPE Release( void)
{
    return NULL;
}

这是构建输出的响应：

1>------ Build started: Project: WinGet, Configuration: Debug Win32 ------
1>Build started 5/29/2011 10:29:15 PM.
1>InitializeBuildStatus:
1>  Touching "Debug\WinGet.unsuccessfulbuild".
1>ClCompile:
1>  All outputs are up-to-date.
1>  All outputs are up-to-date.
1>ManifestResourceCompile:
1>  All outputs are up-to-date.
1>DownloadProgressChange.obj : error LNK2005: "long __stdcall QueryInterface(struct _GUID const &,void * *)" (?QueryInterface@@YGJABU_GUID@@PAPAX@Z) already defined in DownloadCompletedCallback.obj
1>DownloadProgressChange.obj : error LNK2005: "unsigned long __stdcall AddRef(void)" (?AddRef@@YGKXZ) already defined in DownloadCompletedCallback.obj
1>DownloadProgressChange.obj : error LNK2005: "unsigned long __stdcall Release(void)" (?Release@@YGKXZ) already defined in DownloadCompletedCallback.obj
1>WinGet.obj : error LNK2001: unresolved external symbol "private: virtual long __stdcall DownloadCompletedCallback::QueryInterface(struct _GUID const &,void * *)" (?QueryInterface@DownloadCompletedCallback@@EAGJABU_GUID@@PAPAX@Z)
1>WinGet.obj : error LNK2001: unresolved external symbol "private: virtual unsigned long __stdcall DownloadCompletedCallback::AddRef(void)" (?AddRef@DownloadCompletedCallback@@EAGKXZ)
1>WinGet.obj : error LNK2001: unresolved external symbol "private: virtual unsigned long __stdcall DownloadCompletedCallback::Release(void)" (?Release@DownloadCompletedCallback@@EAGKXZ)
1>WinGet.obj : error LNK2001: unresolved external symbol "public: virtual long __stdcall DownloadCompletedCallback::Invoke(struct IDownloadJob *,struct IDownloadCompletedCallbackArgs *)" (?Invoke@DownloadCompletedCallback@@UAGJPAUIDownloadJob@@PAUIDownloadCompletedCallbackArgs@@@Z)
1>WinGet.obj : error LNK2001: unresolved external symbol "public: virtual long __stdcall DownloadProgressChangedCallback::QueryInterface(struct _GUID const &,void * *)" (?QueryInterface@DownloadProgressChangedCallback@@UAGJABU_GUID@@PAPAX@Z)
1>WinGet.obj : error LNK2001: unresolved external symbol "public: virtual unsigned long __stdcall DownloadProgressChangedCallback::AddRef(void)" (?AddRef@DownloadProgressChangedCallback@@UAGKXZ)
1>WinGet.obj : error LNK2001: unresolved external symbol "public: virtual unsigned long __stdcall DownloadProgressChangedCallback::Release(void)" (?Release@DownloadProgressChangedCallback@@UAGKXZ)
1>WinGet.obj : error LNK2001: unresolved external symbol "public: virtual long __stdcall DownloadProgressChangedCallback::Invoke(struct IDownloadJob *,struct IDownloadProgressChangedCallbackArgs *)" (?Invoke@DownloadProgressChangedCallback@@UAGJPAUIDownloadJob@@PAUIDownloadProgressChangedCallbackArgs@@@Z)
1>C:\Users\Nathan\Documents\Visual Studio 2010\Projects\WinGet\Debug\WinGet.exe : fatal error LNK1120: 8 unresolved externals
1>
1>Build FAILED.
1>
1>Time Elapsed 00:00:01.04
========== Build: 0 succeeded, 1 failed, 0 up-to-date, 0 skipped ==========

提前致谢！

Answer 1

在 .cpp 文件中，您忘记将类范围放在函数定义上。它们应该是：

HRESULT STDMETHODCALLTYPE 
    DownloadProgressChangedCallback::Invoke( // <==Note: class! DownloadProgressChangedCallback::
        IDownloadJob *downloadJob,  
        IDownloadProgressChangedCallbackArgs *callbackArgs)
{
    return NULL;
}  

等（两个类中的所有函数。）

---

编辑：在此处添加我在下面添加到 Nemo 的答案中的注释，关于初始化您的 VARIANT：

为了节省您的精力和复杂性，我可以建议您使用 _variant_t班级。这是一个 VARIANT 包装器，可以为您处理很多原本难以处理的内容。以下是一些文档。

要更直接地回答您的问题，您需要查看 VariantInit() 函数 在这里。

Answer 2

在 .cpp 文件中，您需要指定正在定义的成员函数的完全限定名称：

HRESULT STDMETHODCALLTYPE DownloadProgressChangedCallback::Invoke( IDownloadJob *downloadJob,  IDownloadProgressChangedCallbackArgs *callbackArgs)

[等]

如果没有 DownloadProgressChangedCallback:: 前缀，您只需定义一个名为“的全局函数”调用”。链接器抱怨是因为 (a) 您已经执行了两次并且 (b) 您尚未定义您声明的实际成员函数。