QtSupport: Load examples / tutorials only when visible

This speeds up QtCreator startup a bit by not loading the examples all
the time, but only when the user clicks on the "Examples" button.

Change-Id: I8fb3656e871cf3f2f884c5eb12270eba427cd999
Reviewed-by: Eike Ziller <eike.ziller@qt.io>
Reviewed-by: Cristian Adam <cristian.adam@qt.io>

src/plugins/qtsupport/exampleslistmodel.cpp

@@ -342,6 +342,12 @@ Q_GLOBAL_STATIC_WITH_ARGS(QStringList,
 
 void ExamplesViewController::updateExamples()
 {
+    if (!isVisible()) {
+        m_needsUpdateExamples = true;
+        return;
+    }
+    m_needsUpdateExamples = false;
+
     QString examplesInstallPath;
     QString demosInstallPath;
     QVersionNumber qtVersion;
@@ -395,6 +401,20 @@ void ExamplesViewController::updateExamples()
     }
 }
 
+void ExamplesViewController::setVisible(bool visible)
+{
+    if (m_isVisible == visible)
+        return;
+    m_isVisible = visible;
+    if (m_isVisible && m_needsUpdateExamples)
+        updateExamples();
+}
+
+bool ExamplesViewController::isVisible() const
+{
+    return m_isVisible;
+}
+
 void ExampleSetModel::updateQtVersionList()
 {
     QtVersions versions = QtVersionManager::sortVersions(QtVersionManager::versions(

src/plugins/qtsupport/exampleslistmodel.h

@@ -92,11 +92,15 @@ public:
                                     QObject *parent);
 
     void updateExamples();
+    void setVisible(bool isVisible);
+    bool isVisible() const;
 
 private:
     ExampleSetModel *m_exampleSetModel;
     Core::SectionedGridView *m_view;
     bool m_isExamples;
+    bool m_isVisible = false;
+    bool m_needsUpdateExamples = false;
 };
 
 } // namespace Internal

src/plugins/qtsupport/gettingstartedwelcomepage.cpp

@@ -304,7 +304,7 @@ public:
         grid->addWidget(WelcomePageHelpers::panelBar(this), 0, 2);
 
         auto gridView = new SectionedGridView(this);
-        new ExamplesViewController(s_exampleSetModel, gridView, isExamples, this);
+        m_viewController = new ExamplesViewController(s_exampleSetModel, gridView, isExamples, this);
 
         gridView->setItemDelegate(&m_exampleDelegate);
         grid->addWidget(gridView, 1, 1, 1, 2);
@@ -321,9 +321,22 @@ public:
                             + QString("tag:\"%1\" ").arg(tag));
     }
 
+    void showEvent(QShowEvent *event) override
+    {
+        m_viewController->setVisible(true);
+        QWidget::showEvent(event);
+    }
+
+    void hideEvent(QHideEvent *event) override
+    {
+        m_viewController->setVisible(false);
+        QWidget::hideEvent(event);
+    }
+
     const bool m_isExamples;
     ExampleDelegate m_exampleDelegate;
     QLineEdit *m_searcher;
+    ExamplesViewController *m_viewController = nullptr;
 };
 
 QWidget *ExamplesWelcomePage::createWidget() const