sub layer dialog: sort by layer id and feature count numerically (fixes

#16917)

python/gui/qgssublayersdialog.sip

@@ -70,6 +70,12 @@ class QgsSublayersDialog : QDialog
  :rtype: bool
 %End
 
+    int countColumn() const;
+%Docstring
+.. versionadded:: 3.0
+ :rtype: int
+%End
+
   public slots:
     void on_buttonBox_helpRequested();
     int exec();

src/gui/qgssublayersdialog.cpp

@@ -20,6 +20,24 @@
 #include <QTableWidgetItem>
 #include <QPushButton>
 
+class SubLayerItem : public QTreeWidgetItem
+{
+  public:
+    SubLayerItem( const QStringList &strings, int type = QTreeWidgetItem::Type )
+      :  QTreeWidgetItem( strings, type )
+    {}
+
+    bool operator <( const QTreeWidgetItem &other ) const
+    {
+      QgsSublayersDialog *d = qobject_cast<QgsSublayersDialog *>( treeWidget()->parent() );
+      int col = treeWidget()->sortColumn();
+
+      if ( col == 0 || ( col > 0 && d->countColumn() == col ) )
+        return text( col ).toInt() < other.text( col ).toInt();
+      else
+        return text( col ) < other.text( col );
+    }
+};
 
 QgsSublayersDialog::QgsSublayersDialog( ProviderType providerType, const QString &name,
                                         QWidget *parent, Qt::WindowFlags fl )
@@ -123,7 +141,7 @@ void QgsSublayersDialog::populateLayerTable( const QgsSublayersDialog::LayerDefi
       elements << QString::number( item.count );
     if ( mShowType )
       elements << item.type;
-    layersTable->addTopLevelItem( new QTreeWidgetItem( elements ) );
+    layersTable->addTopLevelItem( new SubLayerItem( elements ) );
   }
 
   // resize columns

src/gui/qgssublayersdialog.h

@@ -80,6 +80,10 @@ class GUI_EXPORT QgsSublayersDialog : public QDialog, private Ui::QgsSublayersDi
     //! \since QGIS 3.0
     bool addToGroupCheckbox() const { return mCheckboxAddToGroup->isChecked(); }
 
+    //! Return column with count or -1
+    //! \since QGIS 3.0
+    int countColumn() const { return mShowCount ? 2 : -1; }
+
   public slots:
     void on_buttonBox_helpRequested() { QgsContextHelp::run( metaObject()->className() ); }
     int exec();