legend updates:

- when enabling explicit drawing order, intially take legend order
- when loading projects with explicit drawing order enabled,
  verify that the order is actually fully set and take legend
  order otherwise (fixes #7623)
- store/restore active layer

src/app/legend/qgslegend.cpp

@@ -34,6 +34,7 @@
 #include "qgsvectorlayer.h"
 #include "qgsgenericprojectionselector.h"
 #include "qgsclipboard.h"
+#include "qgsmessagelog.h"
 
 #include <QFont>
 #include <QDomDocument>
@@ -1453,7 +1454,7 @@ void QgsLegend::setDrawingOrder( QList<QgsMapLayer *> layers )
   updateMapCanvasLayerSet();
 }
 
-void QgsLegend::setDrawingOrder( const QList<DrawingOrderInfo>& order )
+void QgsLegend::setDrawingOrder( const QList<DrawingOrderInfo> &order )
 {
   QList<QgsMapCanvasLayer> layers;
 
@@ -1680,7 +1681,7 @@ bool QgsLegend::writeXML( QDomNode &legendnode, QDomDocument &document )
 
 bool QgsLegend::writeXML( QList<QTreeWidgetItem *> items, QDomNode &node, QDomDocument &document )
 {
-  foreach ( QTreeWidgetItem * currentItem, items )
+  foreach ( QTreeWidgetItem *currentItem, items )
   {
     QgsLegendItem *item = dynamic_cast<QgsLegendItem *>( currentItem );
     if ( !item )
@@ -1827,6 +1828,9 @@ bool QgsLegend::readXML( QgsLegendGroup *parent, const QDomNode &node )
     bkMapExtent = mMapCanvas->extent();
   }
 
+  QString activeLayerId = node.toElement().attribute( "activeLayer" );
+  QgsLegendLayer *activeLayer = 0;
+
   const QDomNodeList &l = node.childNodes();
   for ( int i = 0; i < l.count(); i++ )
   {
@@ -1899,6 +1903,9 @@ bool QgsLegend::readXML( QgsLegendGroup *parent, const QDomNode &node )
         continue;
       }
 
+      if ( currentLayer->layer() && currentLayer->layer()->id() == activeLayerId )
+        activeLayer = currentLayer;
+
       if ( currentLayer->layer() && !QgsProject::instance()->layerIsEmbedded( currentLayer->layer()->id() ).isEmpty() )
       {
         // start with already set font style
@@ -1959,22 +1966,40 @@ bool QgsLegend::readXML( QgsLegendGroup *parent, const QDomNode &node )
     }
   }
 
+  if ( activeLayer )
+    setCurrentItem( activeLayer );
+
   //restore canvas extent (could be changed by addLayer calls)
   if ( !bkMapExtent.isEmpty() )
   {
     mMapCanvas->setExtent( bkMapExtent );
   }
+
   return true;
 }
 
 bool QgsLegend::readXML( QDomNode& legendnode )
 {
   clear(); //remove all items first
   mEmbeddedGroups.clear();
-  mUpdateDrawingOrder = legendnode.toElement().attribute( "updateDrawingOrder", "true" ) == "true";
+
+  mUpdateDrawingOrder = true;
+
+  if( !readXML( 0, legendnode ) )
+    return false;
+
+  if( legendnode.toElement().attribute( "updateDrawingOrder", "true" ) != "true" )
+  {
+    if( !verifyDrawingOrder() )
+      QgsMessageLog::logMessage( tr( "Not fully defined drawing order set to legend order." ), tr( "Legend" ), QgsMessageLog::WARNING );
+
+    mUpdateDrawingOrder = false;
+  }
+
   emit updateDrawingOrderChecked( mUpdateDrawingOrder );
   emit updateDrawingOrderUnchecked( !mUpdateDrawingOrder );
-  return readXML( 0, legendnode );
+
+  return true;
 }
 
 QgsLegendLayer* QgsLegend::readLayerFromXML( QDomElement& childelem, bool& isOpen )
@@ -2794,6 +2819,8 @@ void QgsLegend::writeProject( QDomDocument & doc )
 
   QDomElement mapcanvasNode = doc.createElement( "legend" );
   mapcanvasNode.setAttribute( "updateDrawingOrder", mUpdateDrawingOrder ? "true" : "false" );
+  if ( currentLayer() )
+    mapcanvasNode.setAttribute( "activeLayer", currentLayer()->id() );
   qgisNode.appendChild( mapcanvasNode );
   writeXML( mapcanvasNode, doc );
 }
@@ -2946,11 +2973,40 @@ bool QgsLegend::groupEmbedded( QTreeWidgetItem* item ) const
   return mEmbeddedGroups.contains( gItem->text( 0 ) );
 }
 
+bool QgsLegend::verifyDrawingOrder()
+{
+  Q_ASSERT( mUpdateDrawingOrder );
+
+  // check if the drawing order wasn't already initially set
+  bool hasUndefinedOrder = false;
+  for ( QTreeWidgetItemIterator it( this ); *it && !hasUndefinedOrder; it++ )
+  {
+    QgsLegendLayer *ll = dynamic_cast<QgsLegendLayer *>( *it );
+    hasUndefinedOrder |= ll && ll->drawingOrder() < 0;
+  }
+
+  if( !hasUndefinedOrder )
+    return true;
+
+  int i = 0;
+  foreach ( QgsLegendLayer *ll, legendLayers() )
+  {
+    ll->setDrawingOrder( i++ );
+  }
+
+  return false;
+}
+
 void QgsLegend::setUpdateDrawingOrder( bool updateDrawingOrder )
 {
   if ( mUpdateDrawingOrder == updateDrawingOrder )
     return;
 
+  if ( !updateDrawingOrder )
+  {
+    verifyDrawingOrder();
+  }
+
   mUpdateDrawingOrder = updateDrawingOrder;
 
   QgsProject::instance()->dirty( true );

src/app/legend/qgslegend.h

@@ -577,7 +577,7 @@ class QgsLegend : public QTreeWidget
 
     } mPixmaps;
 
-    //! Widget that holds the indicator line //
+    //! Widget that holds the indicator line
     QWidget *mInsertionLine;
 
     QMap< QgsMapLayer::LayerType, QList< LegendLayerAction > > mLegendLayerActionMap;
@@ -588,6 +588,8 @@ class QgsLegend : public QTreeWidget
 
     void updateGroupCheckStates( QTreeWidgetItem *item );
 
+    bool verifyDrawingOrder();
+
   signals:
     void itemAdded( QModelIndex index );
     void itemMoved( QModelIndex oldIndex, QModelIndex newIndex );