revert explicit one-item update request, use dedicated signal

src/library/librarytablemodel.cpp

@@ -101,3 +101,8 @@ TrackModel::Capabilities LibraryTableModel::getCapabilities() const {
             Capability::Properties |
             Capability::Sorting;
 }
+
+void LibraryTableModel::select() {
+    BaseSqlTableModel::select();
+    emit updateTrackCount();
+}

src/library/librarytablemodel.h

@@ -16,4 +16,9 @@ class LibraryTableModel : public BaseSqlTableModel {
     // number of successful additions.
     int addTracks(const QModelIndex& index, const QList<QString>& locations) final;
     TrackModel::Capabilities getCapabilities() const final;
+
+    void select() override;
+
+  signals:
+    void updateTrackCount();
 };

src/library/mixxxlibraryfeature.cpp

@@ -32,7 +32,8 @@ MixxxLibraryFeature::MixxxLibraryFeature(Library* pLibrary,
           m_pLibraryTableModel(nullptr),
           m_pSidebarModel(make_parented<TreeItemModel>(this)),
           m_pMissingView(nullptr),
-          m_pHiddenView(nullptr) {
+          m_pHiddenView(nullptr),
+          m_trackCount{0} {
     QString idColumn = LIBRARYTABLE_ID;
     QStringList columns = {
             LIBRARYTABLE_ID,
@@ -114,6 +115,11 @@ MixxxLibraryFeature::MixxxLibraryFeature(Library* pLibrary,
             pLibrary->trackCollectionManager(),
             "mixxx.db.model.library");
 
+    connect(m_pLibraryTableModel,
+            &LibraryTableModel::updateTrackCount,
+            this,
+            &MixxxLibraryFeature::slotUpdateTrackCount);
+
     std::unique_ptr<TreeItem> pRootItem = TreeItem::newRoot(this);
     pRootItem->appendChild(kMissingTitle);
     pRootItem->appendChild(kHiddenTitle);
@@ -149,7 +155,8 @@ void MixxxLibraryFeature::bindLibraryWidget(WLibrary* pLibraryWidget,
 }
 
 QVariant MixxxLibraryFeature::title() {
-    return tr("Tracks");
+    const QString title = tr("Tracks") + QStringLiteral(" (%1)").arg(m_trackCount);
+    return title;
 }
 
 TreeItemModel* MixxxLibraryFeature::sidebarModel() const {
@@ -183,6 +190,14 @@ void MixxxLibraryFeature::bindSidebarWidget(WLibrarySidebar* pSidebarWidget) {
 }
 #endif
 
+void MixxxLibraryFeature::slotUpdateTrackCount() {
+    m_trackCount = m_pLibraryTableModel->rowCount();
+
+    // Force updating the Tracks sidebar item.
+    // `select` must be false as we don't want to select again
+    emit featureIsLoading(this, false);
+}
+
 void MixxxLibraryFeature::activate() {
     //qDebug() << "MixxxLibraryFeature::activate()";
     emit saveModelState();

src/library/mixxxlibraryfeature.h

@@ -50,6 +50,7 @@ class MixxxLibraryFeature final : public LibraryFeature {
   public slots:
     void activate() override;
     void activateChild(const QModelIndex& index) override;
+    void slotUpdateTrackCount();
 #ifdef __ENGINEPRIME__
     void onRightClick(const QPoint& globalPos) override;
 #endif
@@ -74,6 +75,8 @@ class MixxxLibraryFeature final : public LibraryFeature {
     DlgMissing* m_pMissingView;
     DlgHidden* m_pHiddenView;
 
+    int m_trackCount;
+
 #ifdef __ENGINEPRIME__
     parented_ptr<QAction> m_pExportLibraryAction;