mixerOpen(,,,CALLBACK_WINDOW)，用户通过控制面板改变音量后，窗体接收的是什么事件？

[zxbstrong]

mixerOpen(&hMixer,0,(DWORD)this->m_hWnd,NULL,MIXER_OBJECTF_MIXER | CALLBACK_WINDOW)
我写了一个音量控制程序，想实现这样功能：
用户通过控制面板或其他程序修改音量后，我的程序能发觉并更新。

mixerOpen()函数能够设置消息回调窗口，但我不知道是什么消息？
或者有其他方法，可以发觉系统音量已经改变，但我不想用TIMER

[TianChong]

#include <windows.h>
#include <mmsystem.h>

MMRESULT rc; // Return code.
HMIXER hMixer; // Mixer handle used in mixer API calls.
MIXERCONTROL mxc; // Holds the mixer control data.
MIXERLINE mxl; // Holds the mixer line data.
MIXERLINECONTROLS mxlc; // Obtains the mixer control.

// Open the mixer. This opens the mixer with a deviceID of 0. If you
// have a single sound card/mixer, then this will open it. If you have
// multiple sound cards/mixers, the deviceIDs will be 0, 1, 2, and
// so on.
rc = mixerOpen(&hMixer, 0,0,0,0);
if (MMSYSERR_NOERROR != rc) {
// Couldn't open the mixer.
}

// Initialize MIXERLINE structure.
ZeroMemory(&mxl,sizeof(mxl));
mxl.cbStruct = sizeof(mxl);

// Specify the line you want to get. You are getting the input line
// here. If you want to get the output line, you need to use
// MIXERLINE_COMPONENTTYPE_SRC_WAVEOUT.
mxl.dwComponentType = MIXERLINE_COMPONENTTYPE_DST_WAVEIN;

rc = mixerGetLineInfo((HMIXEROBJ)hMixer, &mxl,
MIXER_GETLINEINFOF_COMPONENTTYPE);
if (MMSYSERR_NOERROR == rc) {
// Couldn't get the mixer line.
}

// Get the control.
ZeroMemory(&mxlc, sizeof(mxlc));
mxlc.cbStruct = sizeof(mxlc);
mxlc.dwLineID = mxl.dwLineID;
mxlc.dwControlType = MIXERCONTROL_CONTROLTYPE_PEAKMETER;
mxlc.cControls = 1;
mxlc.cbmxctrl = sizeof(mxc);
mxlc.pamxctrl = &mxc;
ZeroMemory(&mxc, sizeof(mxc));
mxc.cbStruct = sizeof(mxc);
rc = mixerGetLineControls((HMIXEROBJ)hMixer,&mxlc,
MIXER_GETLINECONTROLSF_ONEBYTYPE);
if (MMSYSERR_NOERROR != rc) {
// Couldn't get the control.
}

// After successfully getting the peakmeter control, the volume range
// will be specified by mxc.Bounds.lMinimum to mxc.Bounds.lMaximum.

MIXERCONTROLDETAILS mxcd; // Gets the control values.
MIXERCONTROLDETAILS_SIGNED volStruct; // Gets the control values.
long volume; // Holds the final volume value.

// Initialize the MIXERCONTROLDETAILS structure
ZeroMemory(&mxcd, sizeof(mxcd));
mxcd.cbStruct = sizeof(mxcd);
mxcd.cbDetails = sizeof(volStruct);
mxcd.dwControlID = mxc.dwControlID;
mxcd.paDetails = &volStruct;
mxcd.cChannels = 1;

// Get the current value of the peakmeter control. Typically, you
// would set a timer in your program to query the volume every 10th
// of a second or so.
rc = mixerGetControlDetails((HMIXEROBJ)hMixer, &mxcd,
MIXER_GETCONTROLDETAILSF_VALUE);
if (MMSYSERR_NOERROR == rc) {
// Couldn't get the current volume.
}
volume = volStruct.lValue;

// Get the absolute value of the volume.
if (volume < 0)
volume = -volume;

[TianChong]

潜龙ROOT(30101) 19:49:30
当我们调用mixeropen时可以传递一个窗口的句柄作为回调窗口，当系统的设置改变，比如音量改变，某个音频线路被静音时，mixer都会给我们的回调窗口发送消息的。

　　一般只有两个消息，如下

afx_msg void OnMLChange(WPARAM wParam, LPARAM lParam);
afx_msg void OnMCChange(WPARAM wParam, LPARAM lParam);

ON_MESSAGE(MM_MIXM_LINE_CHANGE, OnMLChange)
ON_MESSAGE(MM_MIXM_CONTROL_CHANGE, OnMCChange)

潜龙ROOT(30101) 19:49:47
其中MM_MIXM_CONTROL_CHANGE 消息中，发送消息的两个参数代表的意思如下

wParam = (WPARAM) hMixer
lParam = (LPARAM) dwControlID

　　在MM_MIXM_LINE_CHANGE 消息中，发送消息的参数代表的意思如下

wParam = (WPARAM) hMixer
lParam = (LPARAM) dwLineID

[TianChong]

在我们的应用程序中，我们可以在这两个消息处理函数中调整我们的设置，以对应于系统的改变，比如你的代码可以这样写：

void CMixerControlDlg::OnMCChange(WPARAM wParam, LPARAM lParam)
{
　DWORD dwLValue;
　DWORD dwRValue;
　GetVolume(MIXERLINE_COMPONENTTYPE_DST_SPEAKERS, &dwLValue,&dwRValue);
　//GetVolume函数的定义见下面，然后根据返回的值调整滑动条的位置
　m_SliderVolR.SetPos(MAX_VOL_VALUE - dwLValue);
　m_SliderVolL.SetPos(MAX_VOL_VALUE - dwRValue);
　//你也可以在这里调用GetMute查看Volume是否被静音，
}

　　如此你的程序就可以自动的响应系统设置的改变了。

[zxbstrong]

谢谢潜龙ROOT兄！