Add explicit

src/context/contextalbum.h

@@ -44,7 +44,7 @@ class ContextAlbum : public QWidget {
   Q_OBJECT
 
  public:
-  ContextAlbum(QWidget *parent = nullptr);
+  explicit ContextAlbum(QWidget *parent = nullptr);
 
   void Init(AlbumCoverChoiceController *album_cover_choice_controller);
   void SetImage(QImage image = QImage());

src/context/contextalbumsmodel.h

@@ -56,7 +56,7 @@ class ContextAlbumsModel : public SimpleTreeModel<CollectionItem> {
   Q_OBJECT
 
  public:
-  ContextAlbumsModel(CollectionBackend *backend, Application *app, QObject *parent = nullptr);
+  explicit ContextAlbumsModel(CollectionBackend *backend, Application *app, QObject *parent = nullptr);
   ~ContextAlbumsModel();
 
   static const int kPrettyCoverSize;

src/context/contextalbumsview.h

@@ -54,7 +54,7 @@ class ContextItemDelegate : public QStyledItemDelegate {
   Q_OBJECT
 
  public:
-  ContextItemDelegate(QObject *parent);
+  explicit ContextItemDelegate(QObject *parent);
 
  public slots:
   bool helpEvent(QHelpEvent *event, QAbstractItemView *view, const QStyleOptionViewItem &option, const QModelIndex &index);

src/context/contextview.h

@@ -54,7 +54,7 @@ class ContextView : public QWidget {
   Q_OBJECT
 
  public:
-  ContextView(QWidget *parent = nullptr);
+  explicit ContextView(QWidget *parent = nullptr);
 
   void Init(Application *app, CollectionView *collectionview, AlbumCoverChoiceController *album_cover_choice_controller);