QgsEditorWidgetRegistry disconnect signals when mapLayer will be removed (#3186)

Add a method to disconnect signals added when layerIsAdded to QgsMapLayerRegistry. This method is connect to layerWillBeRemoved.

This method will probably fix an issue in QGIS Server about performance deterioration.
Each time a layer is added to QgsMapLayerRegistry by QGIS Server, QgsEditorWidgetRegistry connects to appropriate signals from map layers to load and save style but NEVER disconnects its.

Author: rldhont

src/gui/editorwidgets/core/qgseditorwidgetregistry.cpp

@@ -79,6 +79,7 @@ QgsEditorWidgetRegistry::QgsEditorWidgetRegistry()
   connect( QgsProject::instance(), SIGNAL( readMapLayer( QgsMapLayer*, const QDomElement& ) ), this, SLOT( readMapLayer( QgsMapLayer*, const QDomElement& ) ) );
   // connect( QgsProject::instance(), SIGNAL( writeMapLayer( QgsMapLayer*, QDomElement&, QDomDocument& ) ), this, SLOT( writeMapLayer( QgsMapLayer*, QDomElement&, QDomDocument& ) ) );
 
+  connect( QgsMapLayerRegistry::instance(), SIGNAL( layerWillBeRemoved( QgsMapLayer* ) ), this, SLOT( mapLayerWillBeRemoved( QgsMapLayer* ) ) );
   connect( QgsMapLayerRegistry::instance(), SIGNAL( layerWasAdded( QgsMapLayer* ) ), this, SLOT( mapLayerAdded( QgsMapLayer* ) ) );
 }
 
@@ -318,6 +319,17 @@ void QgsEditorWidgetRegistry::writeMapLayer( QgsMapLayer* mapLayer, QDomElement&
   layerElem.appendChild( editTypesNode );
 }
 
+void QgsEditorWidgetRegistry::mapLayerWillBeRemoved( QgsMapLayer* mapLayer )
+{
+  QgsVectorLayer* vl = qobject_cast<QgsVectorLayer*>( mapLayer );
+
+  if ( vl )
+  {
+    disconnect( vl, SIGNAL( readCustomSymbology( const QDomElement&, QString& ) ), this, SLOT( readSymbology( const QDomElement&, QString& ) ) );
+    disconnect( vl, SIGNAL( writeCustomSymbology( QDomElement&, QDomDocument&, QString& ) ), this, SLOT( writeSymbology( QDomElement&, QDomDocument&, QString& ) ) );
+  }
+}
+
 void QgsEditorWidgetRegistry::mapLayerAdded( QgsMapLayer* mapLayer )
 {
   QgsVectorLayer* vl = qobject_cast<QgsVectorLayer*>( mapLayer );

src/gui/editorwidgets/core/qgseditorwidgetregistry.h

@@ -173,6 +173,13 @@ class GUI_EXPORT QgsEditorWidgetRegistry : public QObject
      */
     void mapLayerAdded( QgsMapLayer* mapLayer );
 
+    /**
+     * Will disconnect to appropriate signals from map layers to load and save style
+     *
+     * @param mapLayer The layer to disconnect
+     */
+    void mapLayerWillBeRemoved( QgsMapLayer* mapLayer );
+
     /**
      * Loads layer symbology for the layer that emitted the signal
      *