applets/dict: Add `loading` in DictionariesModel

loading: true if the engine is downloading dict list from
the Internet, false otherwise.

applets/dict/plugin/dictionariesmodel.cpp

@@ -22,6 +22,7 @@ DictionariesModel::DictionariesModel(QObject *parent)
         endResetModel();
     });
     connect(this, &QAbstractItemModel::modelReset, this, &DictionariesModel::countChanged);
+    connect(&engine, &DictEngine::dictLoadingChanged, this, &DictionariesModel::slotDictLoadingChanged);
 
     engine.requestDicts();
 }
@@ -57,3 +58,15 @@ int DictionariesModel::count() const
 {
     return rowCount();
 }
+
+bool DictionariesModel::loading() const
+{
+    return m_loading;
+}
+
+void DictionariesModel::slotDictLoadingChanged(bool loading)
+{
+    m_loading = loading;
+
+    Q_EMIT loadingChanged();
+}

applets/dict/plugin/dictionariesmodel.h

@@ -19,6 +19,12 @@ class DictionariesModel : public QAbstractListModel
      */
     Q_PROPERTY(int count READ count NOTIFY countChanged)
 
+    /**
+     * @return @c true if the engine is downloading dict list from
+     * the Internet, @c false otherwise.
+     */
+    Q_PROPERTY(bool loading READ loading NOTIFY loadingChanged)
+
 public:
     explicit DictionariesModel(QObject *parent = nullptr);
 
@@ -27,9 +33,11 @@ public:
     QHash<int, QByteArray> roleNames() const override;
 
     int count() const;
+    bool loading() const;
 
 Q_SIGNALS:
     void countChanged();
+    void loadingChanged();
 
 private:
     void setAvailableDicts(const QVariantMap &data);
@@ -39,6 +47,8 @@ private:
         QString description;
     };
     std::vector<AvailableDict> m_availableDicts;
+
+    bool m_loading = false;
 };
 
 #endif