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当我运行我的程序（下面的代码）并通过 USB 电缆插入硬盘驱动器时，WindowProcedure会调用WM_DEVICECHANGEdevice-change event type 的消息DBT_DEVICEARRIVAL。

然而，GetMessage不返回。文档GetMessage说_GetMessage

从调用线程的消息队列中检索消息。

因此，听起来线程的消息队列中没有消息。

为什么我的调用线程的消息队列中没有消息？

如果我的调用线程的消息队列中没有消息，如何/为什么为设备更改事件类型WindowProcedure的消息调用我的函数？WM_DEVICECHANGEDBT_DEVICEARRIVAL

注意：我已经阅读了一些相关的帖子和​​页面。 这个stackoverflow帖子似乎可能是相关的。如果是这样，我怎么知道哪些消息实际放置在消息队列中？

namespace {
    LRESULT CALLBACK WindowProcedure(HWND hWnd, UINT uMsg, WPARAM wParam, LPARAM lParam)
    {

        if( uMsg == WM_DEVICECHANGE )
        {
            switch(wParam)
            {
                case DBT_DEVICEARRIVAL:
                {
                    PostQuitMessage('L');
                    break;
                }

                case DBT_DEVNODES_CHANGED:
                {
                    break;
                }

            }
    }

        return DefWindowProc(hWnd, uMsg, wParam, lParam);
    }
}

BOOL DoRegisterDeviceInterfaceToHwnd(IN GUID InterfaceClassGuid, IN HWND hWnd, OUT HDEVNOTIFY *hDeviceNotify)
{
    DEV_BROADCAST_DEVICEINTERFACE NotificationFilter;

    ZeroMemory( &NotificationFilter, sizeof(NotificationFilter) );
    NotificationFilter.dbcc_size = sizeof(DEV_BROADCAST_DEVICEINTERFACE);
    NotificationFilter.dbcc_devicetype = DBT_DEVTYP_DEVICEINTERFACE;
    NotificationFilter.dbcc_classguid = InterfaceClassGuid;

    *hDeviceNotify = RegisterDeviceNotification( 
        hWnd,                       // events recipient
        &NotificationFilter,        // type of device
        DEVICE_NOTIFY_WINDOW_HANDLE | DEVICE_NOTIFY_ALL_INTERFACE_CLASSES // type of recipient handle
        );

    if ( NULL == *hDeviceNotify ) 
    {
        //ErrorHandler(TEXT("RegisterDeviceNotification"));
        return FALSE;
    }

    return TRUE;
}

int processWindowsMessages()
{
    WNDCLASS windowClass = {};

    windowClass.lpfnWndProc = WindowProcedure;
    LPCSTR windowClassName = "DetecatAndMountMessageOnlyWindow";; 
    windowClass.lpszClassName = windowClassName;
    if (!RegisterClass(&windowClass)) {
        std::cout << "Failed to register window class" << std::endl;
        return 1;
    }

    HWND messageWindow = CreateWindow (windowClassName, 0, 0, 0, 0, 0, 0, HWND_MESSAGE, 0, 0, 0);
    //HWND messageWindow = CreateWindow (windowClassName, 0, 0, 0, 0, 0, 0, (HWND) NULL, 0, 0, 0);
    if (!messageWindow) {
        std::cout << "Failed to create message-only window" << std::endl;
        return 1;
    }
    static HDEVNOTIFY hDeviceNotify;

    DoRegisterDeviceInterfaceToHwnd(GUID_DEVINTERFACE_VOLUME, messageWindow, &hDeviceNotify);

    MSG msg;
    BOOL bRet;
    std::cout << "before loop" << std::endl;

    while ( (bRet = GetMessage (&msg, 0, 0, 0)) != 0 )
    {

        std::cout << "inside loop" << std::endl;
        if (bRet == -1)
        {
            // handle the error and possibly exit
        }
        else
        {
            TranslateMessage(&msg); 
            DispatchMessage(&msg);

        }
    }
    std::cout << msg.wParam << std::endl;
    return msg.wParam;
}

int main()
{
    int result = processWindowsMessages();
    return 0;
}
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1 回答 1

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的文档WM_DEVICECHANGE说：

窗口通过其 WindowProc 函数接收此消息。

这意味着这不是排队的消息。它不放在消息队列中。它不是由 检索的GetMessage。

相反，它被直接发送到窗口的窗口过程。该消息被广播到顶级窗口，并发送到注册的窗口RegisterDeviceNotification。

于 2015-12-04T20:13:52.393 回答