fix: lazy-load genre/playlist views and cap playlist search scrolling

- Defer eager-load scrollbar checks to next event loop iteration via
  QTimer::singleShot(0), fixing initial load not filling the viewport
- Playlist search: eagerly fill viewport, then show "Load more playlists…"
  button instead of infinite scroll to avoid loading thousands of results
- Increase search page size from 8 to 25
- Featured/discover playlists keep auto-scroll behavior unchanged

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/model/tracklistmodel.cpp

@@ -9,21 +9,11 @@ TrackListModel::TrackListModel(QObject *parent)
     : QAbstractTableModel(parent)
 {}
 
-void TrackListModel::setTracks(const QJsonArray &tracks,
+TrackItem TrackListModel::parseTrackItem(const QJsonObject &t,
                                          bool usePosition,
-                               bool useSequential)
+                                         bool useSequential,
+                                         int &seq)
 {
-    beginResetModel();
-    m_tracks.clear();
-    m_tracks.reserve(tracks.size());
-
-    // Parse into a temporary list first so we can detect multi-disc
-    QVector<TrackItem> parsed;
-    parsed.reserve(tracks.size());
-
-    int seq = 1;
-    for (const QJsonValue &v : tracks) {
-        const QJsonObject t = v.toObject();
     TrackItem item;
     item.id               = static_cast<qint64>(t["id"].toDouble());
     item.playlistTrackId  = static_cast<qint64>(t["playlist_track_id"].toDouble());
@@ -66,9 +56,25 @@ void TrackListModel::setTracks(const QJsonArray &tracks,
     item.album   = album["title"].toString();
     item.albumId = album["id"].toString();
 
-        parsed.append(item);
+    return item;
 }
 
+void TrackListModel::setTracks(const QJsonArray &tracks,
+                               bool usePosition,
+                               bool useSequential)
+{
+    beginResetModel();
+    m_tracks.clear();
+    m_tracks.reserve(tracks.size());
+
+    // Parse into a temporary list first so we can detect multi-disc
+    QVector<TrackItem> parsed;
+    parsed.reserve(tracks.size());
+
+    int seq = 1;
+    for (const QJsonValue &v : tracks)
+        parsed.append(parseTrackItem(v.toObject(), usePosition, useSequential, seq));
+
     // Multi-disc only makes sense for album context (not playlists / fav / search)
     int maxDisc = 1;
     if (!usePosition && !useSequential) {
@@ -134,49 +140,8 @@ void TrackListModel::appendTracks(const QJsonArray &tracks,
 
     QVector<TrackItem> parsed;
     parsed.reserve(tracks.size());
-    for (const QJsonValue &v : tracks) {
-        const QJsonObject t = v.toObject();
-        TrackItem item;
-        item.id               = static_cast<qint64>(t["id"].toDouble());
-        item.playlistTrackId  = static_cast<qint64>(t["playlist_track_id"].toDouble());
-        item.discNumber       = t["media_number"].toInt(1);
-        item.duration         = static_cast<qint64>(t["duration"].toDouble());
-        item.streamable       = t["streamable"].toBool(true);
-        item.hiRes            = t["hires_streamable"].toBool();
-        item.raw              = t;
-
-        const QString base    = t["title"].toString();
-        const QString version = t["version"].toString().trimmed();
-        item.title = version.isEmpty() ? base
-                   : base + QStringLiteral(" (") + version + QLatin1Char(')');
-
-        if (useSequential) {
-            item.number = seq++;
-        } else if (usePosition) {
-            const int pos = t["position"].toInt();
-            item.number = pos > 0 ? pos : seq;
-            ++seq;
-        } else {
-            item.number = t["track_number"].toInt();
-        }
-
-        const QJsonObject performer = t["performer"].toObject();
-        item.artist = performer["name"].toString();
-        if (item.artist.isEmpty()) {
-            const QJsonValue n = t["album"].toObject()["artist"].toObject()["name"];
-            item.artist = n.isObject() ? n.toObject()["display"].toString() : n.toString();
-        }
-        if (item.artist.isEmpty()) {
-            const QJsonValue n = t["artist"].toObject()["name"];
-            item.artist = n.isObject() ? n.toObject()["display"].toString() : n.toString();
-        }
-
-        const QJsonObject album = t["album"].toObject();
-        item.album   = album["title"].toString();
-        item.albumId = album["id"].toString();
-
-        parsed.append(item);
-    }
+    for (const QJsonValue &v : tracks)
+        parsed.append(parseTrackItem(v.toObject(), usePosition, useSequential, seq));
 
     if (parsed.isEmpty())
         return;
@@ -210,6 +175,16 @@ void TrackListModel::removeTrack(int row)
     endRemoveRows();
 }
 
+void TrackListModel::notifyFavChanged(qint64 id)
+{
+    for (int r = 0; r < m_tracks.size(); ++r) {
+        if (m_tracks[r].id == id) {
+            const auto idx = index(r, ColTitle);
+            emit dataChanged(idx, idx, {Qt::DecorationRole});
+        }
+    }
+}
+
 void TrackListModel::setFavIds(const QSet<qint64> &ids)
 {
     m_favIds = ids;
@@ -221,23 +196,13 @@ void TrackListModel::setFavIds(const QSet<qint64> &ids)
 void TrackListModel::addFavId(qint64 id)
 {
     m_favIds.insert(id);
-    for (int r = 0; r < m_tracks.size(); ++r) {
-        if (m_tracks[r].id == id) {
-            const auto idx = index(r, ColTitle);
-            emit dataChanged(idx, idx, {Qt::DecorationRole});
-        }
-    }
+    notifyFavChanged(id);
 }
 
 void TrackListModel::removeFavId(qint64 id)
 {
     m_favIds.remove(id);
-    for (int r = 0; r < m_tracks.size(); ++r) {
-        if (m_tracks[r].id == id) {
-            const auto idx = index(r, ColTitle);
-            emit dataChanged(idx, idx, {Qt::DecorationRole});
-        }
-    }
+    notifyFavChanged(id);
 }
 
 void TrackListModel::setPlayingId(qint64 id)

src/model/tracklistmodel.hpp

@@ -105,4 +105,10 @@ private:
 
     // Sort m_tracks in-place without emitting any signals.
     void sortData(int column, Qt::SortOrder order);
+
+    // Parse a single JSON track object into a TrackItem.
+    static TrackItem parseTrackItem(const QJsonObject &t, bool usePosition, bool useSequential, int &seq);
+
+    // Emit dataChanged(DecorationRole) for all rows matching id.
+    void notifyFavChanged(qint64 id);
 };

src/view/genrebrowser.cpp

@@ -9,7 +9,9 @@
 #include <QListWidget>
 #include <QMenu>
 #include <QPushButton>
+#include <QScrollBar>
 #include <QSignalBlocker>
+#include <QTimer>
 #include <QTreeWidgetItem>
 #include <QVBoxLayout>
 
@@ -120,8 +122,18 @@ GenreBrowserView::GenreBrowserView(QobuzBackend *backend, PlayQueue *queue, QWid
     m_playlistList->header()->setSectionResizeMode(3, QHeaderView::ResizeToContents);
     m_playlistList->header()->setStretchLastSection(false);
 
+    auto *playlistPage = new QWidget(this);
+    auto *playlistPageLayout = new QVBoxLayout(playlistPage);
+    playlistPageLayout->setContentsMargins(0, 0, 0, 0);
+    playlistPageLayout->setSpacing(0);
+    playlistPageLayout->addWidget(m_playlistList, 1);
+
+    m_loadMorePlaylistsBtn = new QPushButton(tr("Load more playlists…"), this);
+    m_loadMorePlaylistsBtn->hide();
+    playlistPageLayout->addWidget(m_loadMorePlaylistsBtn);
+
     m_resultsStack->addWidget(m_albumList);
-    m_resultsStack->addWidget(m_playlistList);
+    m_resultsStack->addWidget(playlistPage);
     layout->addWidget(m_resultsStack, 1);
 
     connect(m_backend, &QobuzBackend::genresLoaded,
@@ -180,6 +192,12 @@ GenreBrowserView::GenreBrowserView(QobuzBackend *backend, PlayQueue *queue, QWid
             this, &GenreBrowserView::onAlbumScroll);
     connect(m_playlistList->verticalScrollBar(), &QScrollBar::valueChanged,
             this, &GenreBrowserView::onPlaylistScroll);
+    connect(m_loadMorePlaylistsBtn, &QPushButton::clicked, this, [this] {
+        m_loadMorePlaylistsBtn->hide();
+        requestPlaylistsPage(m_lastPlaylistGenreIds, m_lastPlaylistType,
+                             m_lastPlaylistTags, m_lastPlaylistQuery,
+                             m_playlistOffset, true);
+    });
 
     m_kindCombo->setCurrentIndex(0);
     refreshModeUi();
@@ -391,9 +409,12 @@ void GenreBrowserView::onFeaturedAlbumsLoaded(const QJsonObject &result)
     }
 
     // If the viewport is not scrollable yet, eagerly fetch more pages.
+    // Deferred: the scrollbar maximum isn't updated until after layout runs.
+    QTimer::singleShot(0, this, [this] {
         QScrollBar *bar = m_albumList->verticalScrollBar();
         if (bar && bar->maximum() == 0 && m_albumOffset < m_albumTotal)
             requestAlbumsPage(m_lastAlbumGenreIds, m_lastAlbumType, m_albumOffset, true);
+    });
 }
 
 void GenreBrowserView::onFeaturedPlaylistsLoaded(const QJsonObject &result)
@@ -413,9 +434,11 @@ void GenreBrowserView::onFeaturedPlaylistsLoaded(const QJsonObject &result)
         m_playlistTotal = m_playlistOffset;
     m_loadingPlaylists = false;
 
+    QTimer::singleShot(0, this, [this] {
         QScrollBar *bar = m_playlistList->verticalScrollBar();
         if (bar && bar->maximum() == 0 && m_playlistOffset < m_playlistTotal)
             requestPlaylistsPage(m_lastPlaylistGenreIds, m_lastPlaylistType, m_lastPlaylistTags, m_lastPlaylistQuery, m_playlistOffset, true);
+    });
 }
 
 void GenreBrowserView::onDiscoverPlaylistsLoaded(const QJsonObject &result)
@@ -435,9 +458,11 @@ void GenreBrowserView::onDiscoverPlaylistsLoaded(const QJsonObject &result)
         m_playlistTotal = m_playlistOffset;
     m_loadingPlaylists = false;
 
+    QTimer::singleShot(0, this, [this] {
         QScrollBar *bar = m_playlistList->verticalScrollBar();
         if (bar && bar->maximum() == 0 && m_playlistOffset < m_playlistTotal)
             requestPlaylistsPage(m_lastPlaylistGenreIds, m_lastPlaylistType, m_lastPlaylistTags, m_lastPlaylistQuery, m_playlistOffset, true);
+    });
 }
 
 void GenreBrowserView::onPlaylistSearchLoaded(const QJsonObject &result)
@@ -456,9 +481,25 @@ void GenreBrowserView::onPlaylistSearchLoaded(const QJsonObject &result)
         m_playlistTotal = m_playlistOffset;
     m_loadingPlaylists = false;
 
+    // Eagerly fill the viewport, then switch to a manual "Load more" button.
+    if (m_playlistOffset >= m_playlistTotal) {
+        m_loadMorePlaylistsBtn->hide();
+        m_searchViewportFilled = true;
+    } else if (!m_searchViewportFilled) {
+        QTimer::singleShot(0, this, [this] {
             QScrollBar *bar = m_playlistList->verticalScrollBar();
-    if (bar && bar->maximum() == 0 && m_playlistOffset < m_playlistTotal)
-        requestPlaylistsPage(m_lastPlaylistGenreIds, m_lastPlaylistType, m_lastPlaylistTags, m_lastPlaylistQuery, m_playlistOffset, true);
+            if (bar && bar->maximum() == 0 && m_playlistOffset < m_playlistTotal) {
+                requestPlaylistsPage(m_lastPlaylistGenreIds, m_lastPlaylistType,
+                                     m_lastPlaylistTags, m_lastPlaylistQuery,
+                                     m_playlistOffset, true);
+            } else {
+                m_searchViewportFilled = true;
+                m_loadMorePlaylistsBtn->setVisible(m_playlistOffset < m_playlistTotal);
+            }
+        });
+    } else {
+        m_loadMorePlaylistsBtn->setVisible(true);
+    }
 }
 
 void GenreBrowserView::onSelectionChanged()
@@ -571,6 +612,9 @@ void GenreBrowserView::requestPlaylistsPage(const QString &genreIds, const QStri
         m_loadingPlaylists = false;
         m_playlistOffset = 0;
         m_playlistTotal = 0;
+        m_loadMorePlaylistsBtn->hide();
+        if (type == QStringLiteral("search"))
+            m_searchViewportFilled = false;
     }
 
     m_lastPlaylistGenreIds = genreIds;
@@ -580,7 +624,7 @@ void GenreBrowserView::requestPlaylistsPage(const QString &genreIds, const QStri
     m_loadingPlaylists = true;
 
     if (type == QStringLiteral("search")) {
-        m_backend->searchPlaylists(query, 8, static_cast<quint32>(offset));
+        m_backend->searchPlaylists(query, 25, static_cast<quint32>(offset));
     } else if (type.startsWith(QStringLiteral("discover-"))) {
         m_backend->discoverPlaylists(genreIds, tags, 25, static_cast<quint32>(offset));
     } else {
@@ -608,6 +652,9 @@ void GenreBrowserView::onAlbumScroll(int value)
 
 void GenreBrowserView::onPlaylistScroll(int value)
 {
+    // Search results use a manual "Load more" button instead of infinite scroll.
+    if (m_lastPlaylistType == QStringLiteral("search"))
+        return;
     if (m_loadingPlaylists)
         return;
     if (m_playlistOffset >= m_playlistTotal)

src/view/genrebrowser.hpp

@@ -70,6 +70,8 @@ private:
     QStackedWidget *m_resultsStack = nullptr;
     AlbumListView *m_albumList = nullptr;
     QTreeWidget *m_playlistList = nullptr;
+    QPushButton *m_loadMorePlaylistsBtn = nullptr;
+    bool m_searchViewportFilled = false;
     BrowseMode m_mode = BrowseMode::Genres;
     bool m_genresLoaded = false;
     int m_lastGenreComboIndex = 0;

src/view/maincontent.cpp

@@ -61,14 +61,14 @@ MainContent::MainContent(QobuzBackend *backend, PlayQueue *queue, QWidget *paren
     m_artistView = new ArtistView(backend, queue, this);
     m_genreBrowser = new GenreBrowserView(backend, queue, this);
 
-    m_stack->addWidget(m_welcome);    // 0
-    m_stack->addWidget(tracksPage);   // 1
-    m_stack->addWidget(m_albumList);  // 2
-    m_stack->addWidget(m_artistList); // 3
-    m_stack->addWidget(m_artistView); // 4
-    m_stack->addWidget(m_genreBrowser); // 5
+    m_stack->addWidget(m_welcome);      // PageWelcome
+    m_stack->addWidget(tracksPage);     // PageTracks
+    m_stack->addWidget(m_albumList);    // PageAlbumList
+    m_stack->addWidget(m_artistList);   // PageArtistList
+    m_stack->addWidget(m_artistView);   // PageArtistDetail
+    m_stack->addWidget(m_genreBrowser); // PageGenreBrowser
 
-    m_stack->setCurrentIndex(0);
+    m_stack->setCurrentIndex(PageWelcome);
 
     connect(m_albumList,  &AlbumListView::albumSelected,   this, &MainContent::albumRequested);
     connect(m_artistList, &ArtistListView::artistSelected, this, &MainContent::artistRequested);
@@ -80,7 +80,7 @@ MainContent::MainContent(QobuzBackend *backend, PlayQueue *queue, QWidget *paren
     connect(m_genreBrowser, &GenreBrowserView::playTrackRequested, this, &MainContent::playTrackRequested);
 }
 
-void MainContent::showWelcome()       { m_stack->setCurrentIndex(0); }
+void MainContent::showWelcome()       { m_stack->setCurrentIndex(PageWelcome); }
 
 void MainContent::showAlbum(const QJsonObject &album)
 {
@@ -89,46 +89,46 @@ void MainContent::showAlbum(const QJsonObject &album)
         albumId = QString::number(static_cast<qint64>(album["id"].toDouble()));
     m_header->setAlbum(album, m_favAlbumIds.contains(albumId));
     m_tracks->loadAlbum(album);
-    m_stack->setCurrentIndex(1);
+    m_stack->setCurrentIndex(PageTracks);
 }
 
 void MainContent::showPlaylist(const QJsonObject &playlist, bool isFollowed, bool isOwned)
 {
     m_header->setPlaylist(playlist, isFollowed, isOwned);
     m_tracks->loadPlaylist(playlist);
-    m_stack->setCurrentIndex(1);
+    m_stack->setCurrentIndex(PageTracks);
 }
 
 void MainContent::showFavTracks(const QJsonObject &result)
 {
     m_header->hide();
     m_tracks->loadTracks(result["items"].toArray());
-    m_stack->setCurrentIndex(1);
+    m_stack->setCurrentIndex(PageTracks);
 }
 
 void MainContent::showSearchTracks(const QJsonArray &tracks)
 {
     m_header->hide();
     m_tracks->loadSearchTracks(tracks);
-    m_stack->setCurrentIndex(1);
+    m_stack->setCurrentIndex(PageTracks);
 }
 
 void MainContent::showFavAlbums(const QJsonObject &result)
 {
     m_albumList->setAlbums(result["items"].toArray());
-    m_stack->setCurrentIndex(2);
+    m_stack->setCurrentIndex(PageAlbumList);
 }
 
 void MainContent::showFavArtists(const QJsonObject &result)
 {
     m_artistList->setArtists(result["items"].toArray());
-    m_stack->setCurrentIndex(3);
+    m_stack->setCurrentIndex(PageArtistList);
 }
 
 void MainContent::showArtist(const QJsonObject &artist)
 {
     m_artistView->setArtist(artist);
-    m_stack->setCurrentIndex(4);
+    m_stack->setCurrentIndex(PageArtistDetail);
 }
 
 void MainContent::updateArtistReleases(const QString &releaseType, const QJsonArray &items, bool hasMore, int offset)
@@ -160,14 +160,14 @@ void MainContent::showGenreBrowser()
 {
     m_genreBrowser->ensureGenresLoaded();
     m_genreBrowser->setBrowseMode(GenreBrowserView::BrowseMode::Genres);
-    m_stack->setCurrentIndex(5);
+    m_stack->setCurrentIndex(PageGenreBrowser);
 }
 
 void MainContent::showPlaylistBrowser()
 {
     m_genreBrowser->ensureGenresLoaded();
     m_genreBrowser->setBrowseMode(GenreBrowserView::BrowseMode::PlaylistSearch);
-    m_stack->setCurrentIndex(5);
+    m_stack->setCurrentIndex(PageGenreBrowser);
 }
 
 void MainContent::setCurrentPlaylistFollowed(bool followed)

src/view/maincontent.hpp

@@ -52,6 +52,15 @@ signals:
     void playTrackRequested(qint64 trackId);
 
 private:
+    enum StackPage {
+        PageWelcome      = 0,
+        PageTracks       = 1,
+        PageAlbumList    = 2,
+        PageArtistList   = 3,
+        PageArtistDetail = 4,
+        PageGenreBrowser = 5,
+    };
+
     QobuzBackend        *m_backend    = nullptr;
     QStackedWidget      *m_stack      = nullptr;
     QLabel              *m_welcome    = nullptr;