main: Move some generic initialization out of MixxxMainWindow

The `MixxxMainWindow` class should not be responsible for initializing
`CoreServices`. Mixxx should still be able to work when there is no
`MixxxMainWindow` (e.g. when we switch to a `QQmlApplication` for QML).

src/main.cpp

@@ -23,8 +23,20 @@ constexpr int kFatalErrorOnStartupExitCode = 1;
 constexpr int kParseCmdlineArgsErrorExitCode = 2;
 
 int runMixxx(MixxxApplication* app, const CmdlineArgs& args) {
-    auto coreServices = std::make_shared<mixxx::CoreServices>(args);
-    MixxxMainWindow mainWindow(app, coreServices);
+    const auto pCoreServices = std::make_shared<mixxx::CoreServices>(args);
+    pCoreServices->initializeSettings();
+    pCoreServices->initializeKeyboard();
+
+    MixxxMainWindow mainWindow(app, pCoreServices);
+    app->installEventFilter(&mainWindow);
+
+    QObject::connect(pCoreServices.get(),
+            &mixxx::CoreServices::initializationProgressUpdate,
+            &mainWindow,
+            &MixxxMainWindow::initializationProgressUpdate);
+    pCoreServices->initialize(app);
+    mainWindow.initialize();
+
     // If startup produced a fatal error, then don't even start the
     // Qt event loop.
     if (ErrorDialogHandler::instance()->checkError()) {

src/mixxxmainwindow.cpp

@@ -103,8 +103,6 @@ MixxxMainWindow::MixxxMainWindow(
           m_toolTipsCfg(mixxx::TooltipsPreference::TOOLTIPS_ON) {
     DEBUG_ASSERT(pApp);
     DEBUG_ASSERT(pCoreServices);
-    m_pCoreServices->initializeSettings();
-    m_pCoreServices->initializeKeyboard();
     // These depend on the settings
     createMenuBar();
     m_pMenuBar->hide();
@@ -119,15 +117,9 @@ MixxxMainWindow::MixxxMainWindow(
 
     show();
     pApp->processEvents();
+}
 
-    connect(
-            m_pCoreServices.get(),
-            &mixxx::CoreServices::initializationProgressUpdate,
-            this,
-            &MixxxMainWindow::initializationProgressUpdate);
-
-    m_pCoreServices->initialize(pApp);
-
+void MixxxMainWindow::initialize() {
     UserSettingsPointer pConfig = m_pCoreServices->getSettings();
 
     // Set the visibility of tooltips, default "1" = ON
@@ -161,6 +153,8 @@ MixxxMainWindow::MixxxMainWindow(
 
     initializationProgressUpdate(65, tr("skin"));
 
+    // Install an event filter to catch certain QT events, such as tooltips.
+    // This allows us to turn off tooltips.
     installEventFilter(m_pCoreServices->getKeyboardEventFilter().get());
 
     DEBUG_ASSERT(m_pCoreServices->getPlayerManager());
@@ -269,11 +263,6 @@ MixxxMainWindow::MixxxMainWindow(
         checkDirectRendering();
     }
 
-    // Install an event filter to catch certain QT events, such as tooltips.
-    // This allows us to turn off tooltips.
-    pApp->installEventFilter(this); // The eventfilter is located in this
-                                    // Mixxx class as a callback.
-
     // Try open player device If that fails, the preference panel is opened.
     bool retryClicked;
     do {

src/mixxxmainwindow.h

@@ -48,6 +48,8 @@ class MixxxMainWindow : public QMainWindow {
     MixxxMainWindow(QApplication* app, std::shared_ptr<mixxx::CoreServices> pCoreServices);
     ~MixxxMainWindow() override;
 
+    /// Initialize main window after creation. Should only be called once.
+    void initialize();
     /// creates the menu_bar and inserts the file Menu
     void createMenuBar();
     void connectMenuBar();
@@ -78,6 +80,8 @@ class MixxxMainWindow : public QMainWindow {
     void slotNoDeckPassthroughInputConfigured();
     void slotNoVinylControlInputConfigured();
 
+    void initializationProgressUpdate(int progress, const QString& serviceName);
+
   private slots:
     void slotTooltipModeChanged(mixxx::TooltipsPreference tt);
 
@@ -93,9 +97,6 @@ class MixxxMainWindow : public QMainWindow {
     bool eventFilter(QObject *obj, QEvent *event) override;
     void closeEvent(QCloseEvent *event) override;
 
-  private slots:
-    void initializationProgressUpdate(int progress, const QString& serviceName);
-
   private:
     void initializeWindow();
     void checkDirectRendering();