鉴于本人并非Win32专精，C++也只是学了个大概，因此涉及到底层的部分或有疏漏之处，拙文献丑，还请各位道友多多包涵体谅，能提出修改意见更是感激不尽。

0x00 现代化探索

早在以前写点GDI小程序的时候，巨硬同志就给我留下了这样的不良印象：

Windows很乱复杂，为windows写程序也很乱很复杂。

这导致了我很长一段时间都不敢碰C++，装了VS Community好久一次都没打开过，能用Java+写好的库就用。

可惜这种曲线救国的路终究走不长久，Stackoverflow大法也终究有不管用的时候。

由于早期的电脑设计是一个高度模块化的系统，声音处理被分为了单独的一块，理论上不管是耳机还是扬声器都是由声卡直接管理的。当然现在的声卡（日常笔记本）大都是板载的集成声卡，而且windows上也有Audio Endpoint Device (音频终端设备)这一概念，也不是完全没有路可以走。 然而只要打开过windows设备管理器的人都知道，耳机是没有作为一个设备出现在设备列表里面的。实际上在控制面板-声音中显示的音频输出并非扬声器或者耳机，而是声卡自己配置的音频输出通道，这也印证了“声卡直接接管音频IO的工作”。 （板载声卡是Conexant SmartAudio HD，其他比如Realtek家的估计也差不多，无法验证，欢迎补充）

接下来的这段是关于音频终端的设备的探索，由于对这一块的工作模式没什么了解，因此熟悉的读者可以直接跳过。

所幸打开Conexant SmartAudio HD的驱动详细信息可以看到，在集成声卡的下一层是\Driver\HDAudBus（见下图），度娘告诉我们这个东西的全名是Microsoft UAA Bus Driver for High Definition Audio（针对HD音频的微软UAA总线驱动），而这里的UAA则指的是Universal Audio Architecture (通用音频架构)。这是一个好消息，因为UAA标准是微软自己提出来的，也就意味着我们很可能可以通过windows API直接访问到上面的设备列表。

同样详细信息中的“总线关系”项提供了新的线索： 总线之下的设备包括两项，分别叫做SWD\MMDEVAPI\{0.0.0.00000000}.{c3efdd8a-e470-4841-9617-a42320dd6041}和SWD\MMDEVAPI\{0.0.1.00000000}.{272497f4-319c-4cdd-a2ce-6288c70ebe0a}，猜测两个分别是扬声器与耳机接口（后来被证实），而这个MMDEVAPI则是指的Windows Multimedia Device API (Windows多媒体设备API)。这个线索将我们引到了一个真正的突破：IMMNotificationClient。

0x01 三面红旗

有人说程序员有了一定境界的标志就是，能提出一个没有人研究过的问题。

IMMNotificationClient是何方神圣呢？英语好的道友大概能看出来，它能够提供一个通知设备改变事件的监听器。

事实也确实如此。 通过继承这个类，可以监听到音频终端设备的新增(OnDeviceAdded)、移除(OnDeviceRemoved)、状态更改(OnDeviceStateChanged)、属性值更改(OnPropertyValueChanged)以及默认设备更改(OnDefaultDeviceChanged)。这些方法的定义与用法在MSDN上面都有介绍，在此不多赘述了。

Talk is cheap, show me the code，什么都比不上一个热腾腾的Demo来的有用。 根据这两篇文章（1,2）写了一个简单的示例，代码如下： （基本纯复制/粘贴，代码很乱，iostream和stdio一起用不能忍）

#define SAFE_RELEASE(punk) \ if ((punk) != NULL) \ { (punk)->Release(); (punk) = NULL; } #include <windows.h> #include <setupapi.h> #include <initguid.h> #include <mmdeviceapi.h> #include <Functiondiscoverykeys_devpkey.h> #include "iostream" #include <stdio.h> using namespace std; class CMMNotificationClient : public IMMNotificationClient { public: IMMDeviceEnumerator *m_pEnumerator; CMMNotificationClient(): _cRef(1), m_pEnumerator(NULL) { // 初始化COM ::CoInitialize(NULL); HRESULT hr = S_OK; // 创建接口 hr = CoCreateInstance( __uuidof(MMDeviceEnumerator), NULL, CLSCTX_ALL, __uuidof(IMMDeviceEnumerator), (void**)&m_pEnumerator); if (hr==S_OK) { cout<<"接口创建成功"<<endl; } else { cout<<"接口创建失败"<<endl; } // 注册事件 hr = m_pEnumerator->RegisterEndpointNotificationCallback((IMMNotificationClient*)this); if (hr==S_OK) { cout<<"注册成功"<<endl; } else { cout<<"注册失败"<<endl; } } ~CMMNotificationClient() { SAFE_RELEASE(m_pEnumerator) ::CoUninitialize(); } // IUnknown methods -- AddRef, Release, and QueryInterface private: LONG _cRef; // Private function to print device-friendly name HRESULT _PrintDeviceName(LPCWSTR pwstrId); ULONG STDMETHODCALLTYPE AddRef() { return InterlockedIncrement(&_cRef); } ULONG STDMETHODCALLTYPE Release() { ULONG ulRef = InterlockedDecrement(&_cRef); if (0 == ulRef) { delete this; } return ulRef; } HRESULT STDMETHODCALLTYPE QueryInterface( REFIID riid, VOID **ppvInterface) { if (IID_IUnknown == riid) { AddRef(); *ppvInterface = (IUnknown*)this; } else if (__uuidof(IMMNotificationClient) == riid) { AddRef(); *ppvInterface = (IMMNotificationClient*)this; } else { *ppvInterface = NULL; return E_NOINTERFACE; } return S_OK; } HRESULT STDMETHODCALLTYPE OnDefaultDeviceChanged( EDataFlow flow, ERole role, LPCWSTR pwstrDeviceId) { cout<<"OnDefaultDeviceChanged"<<endl; return S_OK; } HRESULT STDMETHODCALLTYPE OnDeviceAdded(LPCWSTR pwstrDeviceId) { cout<<"OnDeviceAdded"<<endl; return S_OK; }; HRESULT STDMETHODCALLTYPE OnDeviceRemoved(LPCWSTR pwstrDeviceId) { cout<<"OnDeviceRemoved"<<endl; return S_OK; } HRESULT STDMETHODCALLTYPE OnDeviceStateChanged( LPCWSTR pwstrDeviceId, DWORD dwNewState) { cout<<"OnDeviceStateChanged"<<endl; return S_OK; } HRESULT STDMETHODCALLTYPE OnPropertyValueChanged( LPCWSTR pwstrDeviceId, const PROPERTYKEY key) { cout<<"OnPropertyValueChanged"<<endl; _PrintDeviceName(pwstrDeviceId); return S_OK; } }; // Given an endpoint ID string, print the friendly device name. HRESULT CMMNotificationClient::_PrintDeviceName(LPCWSTR pwstrId) { HRESULT hr = S_OK; IMMDevice *pDevice = NULL; IPropertyStore *pProps = NULL; PROPVARIANT varString; CoInitialize(NULL); PropVariantInit(&varString); if (m_pEnumerator == NULL) { // Get enumerator for audio endpoint devices. hr = CoCreateInstance(__uuidof(MMDeviceEnumerator), NULL, CLSCTX_INPROC_SERVER, __uuidof(IMMDeviceEnumerator), (void**)&m_pEnumerator); } if (hr == S_OK) { hr = m_pEnumerator->GetDevice(pwstrId, &pDevice); } if (hr == S_OK) { hr = pDevice->OpenPropertyStore(STGM_READ, &pProps); } if (hr == S_OK) { // Get the endpoint device's friendly-name property. hr = pProps->GetValue(PKEY_Device_FriendlyName, &varString); } printf("----------------------\nDevice name: \"%S\"\n" " Endpoint ID string: \"%S\"\n", (hr == S_OK) ? varString.pwszVal : L"null device", (pwstrId != NULL) ? pwstrId : L"null ID"); PropVariantClear(&varString); SAFE_RELEASE(pProps) SAFE_RELEASE(pDevice) return hr; } int main(int argc, TCHAR* argv[], TCHAR* envp[]) { CMMNotificationClient mmClient; cin.get(); return 0; }

注：一开始导入windows.h、setupapi.h、initguid.h是因为_PrintDeviceName里面用的PKEY_Device_FriendlyName常量需要。理论上这个常量只要直接导入Functiondiscoverykeys_devpkey.h就可以了，不过可能因为Dev C++自带的MinGW版本问题，不加前面这三个会报undefined reference to 'PKEY_Device_FriendlyName'，就按网上的解决方法加上了，各位有更好的欢迎提出。

编译运行结果如下，其间插拔两次耳机： （为阅读效果做了部分处理，以//开头的行是注释）

接口创建成功 注册成功 //第一次插入耳机 OnPropertyValueChanged ---------------------- Device name: "" Endpoint ID string: "{0.0.0.00000000}.{c3efdd8a-e470-4841-9617-a42320dd6041}" OnPropertyValueChanged ---------------------- Device name: "" Endpoint ID string: "{0.0.0.00000000}.{c3efdd8a-e470-4841-9617-a42320dd6041}" OnPropertyValueChanged ---------------------- Device name: "" Endpoint ID string: "{0.0.0.00000000}.{c3efdd8a-e470-4841-9617-a42320dd6041}" OnPropertyValueChanged ---------------------- Device name: "" Endpoint ID string: "{0.0.0.00000000}.{c3efdd8a-e470-4841-9617-a42320dd6041}" OnPropertyValueChanged ---------------------- Device name: "" Endpoint ID string: "{0.0.0.00000000}.{c3efdd8a-e470-4841-9617-a42320dd6041}" OnPropertyValueChanged ---------------------- Device name: "" Endpoint ID string: "{0.0.0.00000000}.{c3efdd8a-e470-4841-9617-a42320dd6041}" OnPropertyValueChanged ---------------------- Device name: "" Endpoint ID string: "{0.0.0.00000000}.{c3efdd8a-e470-4841-9617-a42320dd6041}" // 注意这里是External OnPropertyValueChanged ---------------------- Device name: "External Microphone (Conexant SmartAudio HD)" Endpoint ID string: "{0.0.1.00000000}.{272497f4-319c-4cdd-a2ce-6288c70ebe0a}" OnPropertyValueChanged ---------------------- Device name: "External Microphone (Conexant SmartAudio HD)" Endpoint ID string: "{0.0.1.00000000}.{272497f4-319c-4cdd-a2ce-6288c70ebe0a}" OnPropertyValueChanged ---------------------- Device name: "External Microphone (Conexant SmartAudio HD)" Endpoint ID string: "{0.0.1.00000000}.{272497f4-319c-4cdd-a2ce-6288c70ebe0a}" OnPropertyValueChanged ---------------------- Device name: "External Microphone (Conexant SmartAudio HD)" Endpoint ID string: "{0.0.1.00000000}.{272497f4-319c-4cdd-a2ce-6288c70ebe0a}" OnPropertyValueChanged ---------------------- Device name: "External Microphone (Conexant SmartAudio HD)" Endpoint ID string: "{0.0.1.00000000}.{272497f4-319c-4cdd-a2ce-6288c70ebe0a}" OnPropertyValueChanged ---------------------- Device name: "External Microphone (Conexant SmartAudio HD)" Endpoint ID string: "{0.0.1.00000000}.{272497f4-319c-4cdd-a2ce-6288c70ebe0a}" // 第一次拔出耳机 OnPropertyValueChanged ---------------------- Device name: "" Endpoint ID string: "{0.0.0.00000000}.{c3efdd8a-e470-4841-9617-a42320dd6041}" OnPropertyValueChanged ---------------------- Device name: "" Endpoint ID string: "{0.0.0.00000000}.{c3efdd8a-e470-4841-9617-a42320dd6041}" OnPropertyValueChanged ---------------------- Device name: "" Endpoint ID string: "{0.0.0.00000000}.{c3efdd8a-e470-4841-9617-a42320dd6041}" OnPropertyValueChanged ---------------------- Device name: "" Endpoint ID string: "{0.0.0.00000000}.{c3efdd8a-e470-4841-9617-a42320dd6041}" OnPropertyValueChanged ---------------------- Device name: "" Endpoint ID string: "{0.0.0.00000000}.{c3efdd8a-e470-4841-9617-a42320dd6041}" OnPropertyValueChanged ---------------------- Device name: "" Endpoint ID string: "{0.0.0.00000000}.{c3efdd8a-e470-4841-9617-a42320dd6041}" OnPropertyValueChanged ---------------------- Device name: "" Endpoint ID string: "{0.0.0.00000000}.{c3efdd8a-e470-4841-9617-a42320dd6041}" OnPropertyValueChanged ---------------------- Device name: "" Endpoint ID string: "{0.0.0.00000000}.{c3efdd8a-e470-4841-9617-a42320dd6041}" OnPropertyValueChanged ---------------------- Device name: "" Endpoint ID string: "{0.0.0.00000000}.{c3efdd8a-e470-4841-9617-a42320dd6041}" OnPropertyValueChanged ---------------------- Device name: "" Endpoint ID string: "{0.0.0.00000000}.{c3efdd8a-e470-4841-9617-a42320dd6041}" // 注意这里是Internal OnPropertyValueChanged ---------------------- Device name: "Internal Microphone (Conexant SmartAudio HD)" Endpoint ID string: "{0.0.1.00000000}.{272497f4-319c-4cdd-a2ce-6288c70ebe0a}" OnPropertyValueChanged ---------------------- Device name: "Internal Microphone (Conexant SmartAudio HD)" Endpoint ID string: "{0.0.1.00000000}.{272497f4-319c-4cdd-a2ce-6288c70ebe0a}" OnPropertyValueChanged ---------------------- Device name: "Internal Microphone (Conexant SmartAudio HD)" Endpoint ID string: "{0.0.1.00000000}.{272497f4-319c-4cdd-a2ce-6288c70ebe0a}" OnPropertyValueChanged ---------------------- Device name: "Internal Microphone (Conexant SmartAudio HD)" Endpoint ID string: "{0.0.1.00000000}.{272497f4-319c-4cdd-a2ce-6288c70ebe0a}" OnPropertyValueChanged ---------------------- Device name: "Internal Microphone (Conexant SmartAudio HD)" Endpoint ID string: "{0.0.1.00000000}.{272497f4-319c-4cdd-a2ce-6288c70ebe0a}" OnPropertyValueChanged ---------------------- Device name: "Internal Microphone (Conexant SmartAudio HD)" Endpoint ID string: "{0.0.1.00000000}.{272497f4-319c-4cdd-a2ce-6288c70ebe0a}" // 第二次插入耳机，输出内容与第一次基本相同 OnPropertyValueChanged ---------------------- Device name: "" Endpoint ID string: "{0.0.0.00000000}.{c3efdd8a-e470-4841-9617-a42320dd6041}" OnPropertyValueChanged ---------------------- Device name: "" Endpoint ID string: "{0.0.0.00000000}.{c3efdd8a-e470-4841-9617-a42320dd6041}" OnPropertyValueChanged ---------------------- Device name: "" Endpoint ID string: "{0.0.0.00000000}.{c3efdd8a-e470-4841-9617-a42320dd6041}" OnPropertyValueChanged ---------------------- Device name: "" Endpoint ID string: "{0.0.0.00000000}.{c3efdd8a-e470-4841-9617-a42320dd6041}" OnPropertyValueChanged ---------------------- Device name: "" Endpoint ID string: "{0.0.0.00000000}.{c3efdd8a-e470-4841-9617-a42320dd6041}" OnPropertyValueChanged ---------------------- Device name: "" Endpoint ID string: "{0.0.0.00000000}.{c3efdd8a-e470-4841-9617-a42320dd6041}" OnPropertyValueChanged ---------------------- Device name: "" Endpoint ID string: "{0.0.0.00000000}.{c3efdd8a-e470-4841-9617-a42320dd6041}" OnPropertyValueChanged ---------------------- Device name: "External Microphone (Conexant SmartAudio HD)" Endpoint ID string: "{0.0.1.00000000}.{272497f4-319c-4cdd-a2ce-6288c70ebe0a}" OnPropertyValueChanged ---------------------- Device name: "External Microphone (Conexant SmartAudio HD)" Endpoint ID string: "{0.0.1.00000000}.{272497f4-319c-4cdd-a2ce-6288c70ebe0a}" OnPropertyValueChanged ---------------------- Device name: "External Microphone (Conexant SmartAudio HD)" Endpoint ID string: "{0.0.1.00000000}.{272497f4-319c-4cdd-a2ce-6288c70ebe0a}" OnPropertyValueChanged ---------------------- Device name: "External Microphone (Conexant SmartAudio HD)" Endpoint ID string: "{0.0.1.00000000}.{272497f4-319c-4cdd-a2ce-6288c70ebe0a}" OnPropertyValueChanged ---------------------- Device name: "External Microphone (Conexant SmartAudio HD)" Endpoint ID string: "{0.0.1.00000000}.{272497f4-319c-4cdd-a2ce-6288c70ebe0a}" OnPropertyValueChanged ---------------------- Device name: "External Microphone (Conexant SmartAudio HD)" Endpoint ID string: "{0.0.1.00000000}.{272497f4-319c-4cdd-a2ce-6288c70ebe0a}" // 第二次拔出耳机 OnPropertyValueChanged ---------------------- Device name: "" Endpoint ID string: "{0.0.0.00000000}.{c3efdd8a-e470-4841-9617-a42320dd6041}" OnPropertyValueChanged ---------------------- Device name: "" Endpoint ID string: "{0.0.0.00000000}.{c3efdd8a-e470-4841-9617-a42320dd6041}" OnPropertyValueChanged ---------------------- Device name: "" Endpoint ID string: "{0.0.0.00000000}.{c3efdd8a-e470-4841-9617-a42320dd6041}" OnPropertyValueChanged ---------------------- Device name: "" Endpoint ID string: "{0.0.0.00000000}.{c3efdd8a-e470-4841-9617-a42320dd6041}" OnPropertyValueChanged ---------------------- Device name: "" Endpoint ID string: "{0.0.0.00000000}.{c3efdd8a-e470-4841-9617-a42320dd6041}" OnPropertyValueChanged ---------------------- Device name: "" Endpoint ID string: "{0.0.0.00000000}.{c3efdd8a-e470-4841-9617-a42320dd6041}" OnPropertyValueChanged ---------------------- Device name: "" Endpoint ID string: "{0.0.0.00000000}.{c3efdd8a-e470-4841-9617-a42320dd6041}" OnPropertyValueChanged ---------------------- Device name: "" Endpoint ID string: "{0.0.0.00000000}.{c3efdd8a-e470-4841-9617-a42320dd6041}" OnPropertyValueChanged ---------------------- Device name: "" Endpoint ID string: "{0.0.0.00000000}.{c3efdd8a-e470-4841-9617-a42320dd6041}" OnPropertyValueChanged ---------------------- Device name: "" Endpoint ID string: "{0.0.0.00000000}.{c3efdd8a-e470-4841-9617-a42320dd6041}" OnPropertyValueChanged ---------------------- Device name: "Internal Microphone (Conexant SmartAudio HD)" Endpoint ID string: "{0.0.1.00000000}.{272497f4-319c-4cdd-a2ce-6288c70ebe0a}" OnPropertyValueChanged ---------------------- Device name: "Internal Microphone (Conexant SmartAudio HD)" Endpoint ID string: "{0.0.1.00000000}.{272497f4-319c-4cdd-a2ce-6288c70ebe0a}" OnPropertyValueChanged ---------------------- Device name: "Internal Microphone (Conexant SmartAudio HD)" Endpoint ID string: "{0.0.1.00000000}.{272497f4-319c-4cdd-a2ce-6288c70ebe0a}" OnPropertyValueChanged ---------------------- Device name: "Internal Microphone (Conexant SmartAudio HD)" Endpoint ID string: "{0.0.1.00000000}.{272497f4-319c-4cdd-a2ce-6288c70ebe0a}" OnPropertyValueChanged ---------------------- Device name: "Internal Microphone (Conexant SmartAudio HD)" Endpoint ID string: "{0.0.1.00000000}.{272497f4-319c-4cdd-a2ce-6288c70ebe0a}" OnPropertyValueChanged ---------------------- Device name: "Internal Microphone (Conexant SmartAudio HD)" Endpoint ID string: "{0.0.1.00000000}.{272497f4-319c-4cdd-a2ce-6288c70ebe0a}"

很可惜的是本来期望会有的反映的OnDeviceAdded/OnDeviceRemoved并没有输出，耳机插拔只在OnProperyValueChanged里面有所反映，而且唯一的不同点只在于设备名称以External还是Internal开头。

不过好消息是，这样作为检测耳机插拔就基本上够了。使用IMMNotificationClient在理论上是可行的。 另外就是，这也验证了我们前面的猜想：驱动详细信息中的总线关系的两个子项正是我们的扬声器和耳机——输出的Endpoint ID string和前面的值完全相同。

至于具体怎么实现，又怎么与Java代码相集成（见总起篇），由于篇幅所限，我们下篇文章不见不散。