Make QgsVectorLayer::setDataSource maintain renderer where possible

Author: nyalldawson

python/core/qgsvectorlayer.sip

@@ -577,7 +577,17 @@ class QgsVectorLayer : QgsMapLayer
      */
     virtual long featureCount() const;
 
-    void setDataSource(QString dataSource, QString baseName, QString provider, bool loadDefaultStyleFlag = true);
+    /**
+     * Update the data source of the layer. The layer's renderer and legend will be preserved only
+     * if the geometry type of the new data source matches the current geometry type of the layer.
+     * @param dataSource new layer data source
+     * @param baseName base name of the layer
+     * @param provider provider string
+     * @param loadDefaultStyleFlag set to true to reset the layer's style to the default for the
+     * data source
+     * @note added in QGIS 2.10
+     */
+    void setDataSource( QString dataSource, QString baseName, QString provider, bool loadDefaultStyleFlag = false );
 
     /**
      * Number of features rendered with specified symbol. Features must be first

src/core/qgsvectorlayer.cpp

@@ -1330,6 +1330,8 @@ bool QgsVectorLayer::readXml( const QDomNode& layer_node )
 
 void QgsVectorLayer::setDataSource( QString dataSource, QString baseName, QString provider, bool loadDefaultStyleFlag )
 {
+  QGis::GeometryType oldGeomType = geometryType();
+
   mDataSource = dataSource;
   mLayerName = capitaliseLayerName( baseName );
   setLayerName( mLayerName );
@@ -1340,24 +1342,29 @@ void QgsVectorLayer::setDataSource( QString dataSource, QString baseName, QStrin
     // Always set crs
     setCoordinateSystem();
 
-    // check if there is a default style / propertysheet defined
-    // for this layer and if so apply it
-    bool defaultLoadedFlag = false;
-    if ( loadDefaultStyleFlag )
+    // reset style if loading default style, style is missing, or geometry type has changed
+    if ( !rendererV2() || !legend() || oldGeomType != geometryType() || loadDefaultStyleFlag )
     {
-      loadDefaultStyle( defaultLoadedFlag );
-    }
+      // check if there is a default style / propertysheet defined
+      // for this layer and if so apply it
+      bool defaultLoadedFlag = false;
+      if ( loadDefaultStyleFlag )
+      {
+        loadDefaultStyle( defaultLoadedFlag );
+      }
 
-    // if the default style failed to load or was disabled use some very basic defaults
-    if ( !defaultLoadedFlag && hasGeometryType() )
-    {
-      // add single symbol renderer
-      setRendererV2( QgsFeatureRendererV2::defaultRenderer( geometryType() ) );
-    }
+      // if the default style failed to load or was disabled use some very basic defaults
+      if ( !defaultLoadedFlag && hasGeometryType() )
+      {
+        // add single symbol renderer
+        setRendererV2( QgsFeatureRendererV2::defaultRenderer( geometryType() ) );
+      }
 
-    setLegend( QgsMapLayerLegend::defaultVectorLegend( this ) );
+      setLegend( QgsMapLayerLegend::defaultVectorLegend( this ) );
+    }
 
     connect( QgsMapLayerRegistry::instance(), SIGNAL( layerWillBeRemoved( QString ) ), this, SLOT( checkJoinLayerRemove( QString ) ) );
+    emit repaintRequested();
   }
 }
 

src/core/qgsvectorlayer.h

@@ -1078,9 +1078,16 @@ class CORE_EXPORT QgsVectorLayer : public QgsMapLayer
     long featureCount( QgsSymbolV2* symbol );
 
     /**
-     * Update the data source of the layer
-     */
-    void setDataSource( QString dataSource, QString baseName, QString provider , bool loadDefaultStyleFlag = false );
+     * Update the data source of the layer. The layer's renderer and legend will be preserved only
+     * if the geometry type of the new data source matches the current geometry type of the layer.
+     * @param dataSource new layer data source
+     * @param baseName base name of the layer
+     * @param provider provider string
+     * @param loadDefaultStyleFlag set to true to reset the layer's style to the default for the
+     * data source
+     * @note added in QGIS 2.10
+     */
+    void setDataSource( QString dataSource, QString baseName, QString provider, bool loadDefaultStyleFlag = false );
 
     /**
      * Count features for symbols. Feature counts may be get by featureCount( QgsSymbolV2*).