juce中的消息循环及其处理

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START_JUCE_APPLICATION (PluginHostApp) 展开这个宏

#ifdef DOXYGEN #define START_JUCE_APPLICATION(AppClass)#elif JUCE_ANDROID #define START_JUCE_APPLICATION(AppClass) \   juce::JUCEApplicationBase* juce_CreateApplication() { return new AppClass(); }#else #if JUCE_WINDOWS && ! defined (_CONSOLE)  #define JUCE_MAIN_FUNCTION       int __stdcall WinMain (struct HINSTANCE__*, struct HINSTANCE__*, char*, int)  #define JUCE_MAIN_FUNCTION_ARGS #else  #define JUCE_MAIN_FUNCTION       int main (int argc, char* argv[])  #define JUCE_MAIN_FUNCTION_ARGS  argc, (const char**) argv #endif #define START_JUCE_APPLICATION(AppClass) \    static juce::JUCEApplicationBase* juce_CreateApplication() { return new AppClass(); } \    extern "C" JUCE_MAIN_FUNCTION \    { \        juce::JUCEApplicationBase::createInstance = &juce_CreateApplication; \        return juce::JUCEApplicationBase::main (JUCE_MAIN_FUNCTION_ARGS); \    }#endif

可以看到调用了main函数，同里还可以看到这里创建了应用程序的实例的创建函数指针，这个指针将在main函数中被调用

juce::JUCEApplicationBase::createInstance

这时一直找到了main函数

int JUCEApplicationBase::main()
{
    ScopedJuceInitialiser_GUI libraryInitialiser;
    jassert (createInstance != nullptr);
    const ScopedPointer<JUCEApplicationBase> app (createInstance());
    jassert (app != nullptr);
    if (! app->initialiseApp())
        return 0;
    JUCE_TRY
    {
        // loop until a quit message is received..
        MessageManager::getInstance()->runDispatchLoop();
    }
    JUCE_CATCH_EXCEPTION
    return app->shutdownApp();
}

调用消息循环，同时这个地方还调用了app的初始化函数，这是个虚函数


void MessageManager::runDispatchLoop()
{
    runDispatchLoopUntil (-1);
}

进入循环

bool MessageManager::runDispatchLoopUntil (int millisecondsToRunFor)
{
    jassert (isThisTheMessageThread()); // must only be called by the message thread
    const int64 endTime = Time::currentTimeMillis() + millisecondsToRunFor;
    while (! quitMessageReceived)
    {
        JUCE_TRY
        {
            if (! dispatchNextMessageOnSystemQueue (millisecondsToRunFor >= 0))
                Thread::sleep (1);
        }
        JUCE_CATCH_EXCEPTION
        if (millisecondsToRunFor >= 0 && Time::currentTimeMillis() >= endTime)
            break;
    }
    return ! quitMessageReceived;
}

//==============================================================================
bool MessageManager::dispatchNextMessageOnSystemQueue (const bool returnIfNoPendingMessages)
{
    using namespace WindowsMessageHelpers;
    MSG m;
    if (returnIfNoPendingMessages && ! PeekMessage (&m, (HWND) 0, 0, 0, PM_NOREMOVE))
        return false;
    if (GetMessage (&m, (HWND) 0, 0, 0) >= 0)
    {
        if (m.message == specialId && m.hwnd == juce_messageWindowHandle)
        {
            dispatchMessageFromLParam (m.lParam);
        }
        else if (m.message == WM_QUIT)
        {
            if (JUCEApplicationBase* const app = JUCEApplicationBase::getInstance())
                app->systemRequestedQuit();
        }
        else if (isEventBlockedByModalComps == nullptr || ! isEventBlockedByModalComps (m))
        {
            if ((m.message == WM_LBUTTONDOWN || m.message == WM_RBUTTONDOWN)
                  && ! JuceWindowIdentifier::isJUCEWindow (m.hwnd))
            {
                // if it's someone else's window being clicked on, and the focus is
                // currently on a juce window, pass the kb focus over..
                HWND currentFocus = GetFocus();
                if (currentFocus == 0 || JuceWindowIdentifier::isJUCEWindow (currentFocus))
                    SetFocus (m.hwnd);
            }
            TranslateMessage (&m);
            DispatchMessage (&m);
        }
    }
    return true;
}

这个边的代码看! PeekMessage (&m, (HWND) 0, 0, 0, PM_NOREMOVE) 这个用来检查是否有消息，然后使用GetMessage(&m,(HWND)0,0,0) 来取出消息

这里的specialId 是发送消息的时候设置的。

    const unsigned int specialId   = WM_APP + 0x4400;
    const unsigned int broadcastId = WM_APP + 0x4403;

同时，这里还处理了

            if ((m.message == WM_LBUTTONDOWN || m.message == WM_RBUTTONDOWN)
                  && ! JuceWindowIdentifier::isJUCEWindow (m.hwnd))
            {
                // if it's someone else's window being clicked on, and the focus is
                // currently on a juce window, pass the kb focus over..
                HWND currentFocus = GetFocus();
                if (currentFocus == 0 || JuceWindowIdentifier::isJUCEWindow (currentFocus))
                    SetFocus (m.hwnd);
            }

接边接着看两个分支语句是如何去处理的

    void dispatchMessageFromLParam (LPARAM lParam)
    {
        MessageManager::MessageBase* const message = reinterpret_cast <MessageManager::MessageBase*> (lParam);
        JUCE_TRY
        {
            message->messageCallback();
        }
        JUCE_CATCH_EXCEPTION
        message->decReferenceCount();
    }

message->decReferenceCount(); 如果计数为零的话则销毁消息

特别说明，在app的初始中进行了一系列的初始化操作，包括创口的创建等，具体可以参见juce的示例代码，窗口的具体创建过程请参见后续文章。

 void initialise (const String& commandLine)    {        // initialise our settings file..        PropertiesFile::Options options;        options.applicationName     = "Juce Audio Plugin Host";        options.filenameSuffix      = "settings";        options.osxLibrarySubFolder = "Preferences";        appProperties = new ApplicationProperties();        appProperties->setStorageParameters (options);        LookAndFeel::setDefaultLookAndFeel (&lookAndFeel);        mainWindow = new MainHostWindow();        mainWindow->setUsingNativeTitleBar (true);        commandManager.registerAllCommandsForTarget (this);        commandManager.registerAllCommandsForTarget (mainWindow);        mainWindow->menuItemsChanged();        if (commandLine.isNotEmpty()             && ! commandLine.trimStart().startsWith ("-")             && mainWindow->getGraphEditor() != nullptr)            mainWindow->getGraphEditor()->graph.loadFrom (File::getCurrentWorkingDirectory()                                                            .getChildFile (commandLine), true);    }

说明：分析不一定正确，仅供参考。

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