Allow retrieval of project layer order through QgsProject

Previously this was only accessible through app

python/core/qgsproject.sip

@@ -487,6 +487,9 @@ class QgsProject : QObject, QgsExpressionContextGenerator
      */
     void reloadAllLayers();
 
+    QList< QgsMapLayer * > layerOrder() const;
+    void setLayerOrder( const QList< QgsMapLayer * > &order );
+
   signals:
     //! emitted when project is being read
     void readProject( const QDomDocument& );
@@ -623,12 +626,12 @@ class QgsProject : QObject, QgsExpressionContextGenerator
      */
     //TODO QGIS 3.0 - rename to past tense
     void removeAll();
+    void layersAdded( const QList<QgsMapLayer *> &layers );
 
-    void layersAdded( const QList<QgsMapLayer *>& layers );
+    void layerWasAdded( QgsMapLayer *layer );
+    void legendLayersAdded( const QList<QgsMapLayer *> &layers );
 
-    void layerWasAdded( QgsMapLayer* layer );
-
-    void legendLayersAdded( const QList<QgsMapLayer*>& layers );
+    void layerOrderChanged();
 
   public slots:
     /**

src/core/qgsproject.cpp

@@ -44,6 +44,7 @@
 #include "qgsvectordataprovider.h"
 #include "qgsprojectbadlayerhandler.h"
 #include "qgssettings.h"
+#include "qgsmaplayerlistutils.h"
 
 #include <QApplication>
 #include <QFileInfo>
@@ -460,6 +461,7 @@ void QgsProject::clear()
   mEvaluateDefaultValues = false;
   mDirty = false;
   mCustomVariables.clear();
+  mLayerOrder.clear();
 
   mEmbeddedLayers.clear();
   mRelationManager->clear();
@@ -881,6 +883,20 @@ bool QgsProject::read()
   // load embedded groups and layers
   loadEmbeddedNodes( mRootGroup );
 
+  // load layer order
+  QList< QgsMapLayer * > layerOrder;
+  QDomNodeList layerOrderNodes = doc->elementsByTagName( QStringLiteral( "layerorder" ) );
+  if ( layerOrderNodes.count() )
+  {
+    QDomElement layerOrderElem = layerOrderNodes.at( 0 ).toElement();
+    for ( int i = 0; i < layerOrderElem.childNodes().count(); ++i )
+    {
+      QDomElement layerElem = layerOrderElem.childNodes().at( i ).toElement();
+      layerOrder << mMapLayers.value( layerElem.attribute( QStringLiteral( "id" ) ) );
+    }
+  }
+  setLayerOrder( layerOrder );
+
   // now that layers are loaded, we can resolve layer tree's references to the layers
   mRootGroup->resolveReferences( this );
 
@@ -1244,6 +1260,16 @@ bool QgsProject::write()
 
   qgisNode.appendChild( projectLayersNode );
 
+  QDomElement layerOrderNode = doc->createElement( QStringLiteral( "layerorder" ) );
+  Q_FOREACH ( QgsMapLayer *layer, layerOrder() )
+  {
+    QDomElement mapLayerElem = doc->createElement( QStringLiteral( "layer" ) );
+    mapLayerElem.setAttribute( QStringLiteral( "id" ), layer->id() );
+    layerOrderNode.appendChild( mapLayerElem );
+  }
+  qgisNode.appendChild( layerOrderNode );
+
+
   // now add the optional extra properties
 
   dump_( mProperties );
@@ -2091,6 +2117,8 @@ void QgsProject::removeMapLayers( const QList<QgsMapLayer *> &layers )
   QStringList layerIds;
   QList<QgsMapLayer *> layerList;
 
+  bool layerOrderHasChanged = false;
+  QList< QgsMapLayer * > currentOrder = layerOrder();
   Q_FOREACH ( QgsMapLayer *layer, layers )
   {
     // check layer and the registry contains it
@@ -2098,6 +2126,7 @@ void QgsProject::removeMapLayers( const QList<QgsMapLayer *> &layers )
     {
       layerIds << layer->id();
       layerList << layer;
+      layerOrderHasChanged = layerOrderHasChanged || currentOrder.contains( layer );
     }
   }
 
@@ -2121,6 +2150,8 @@ void QgsProject::removeMapLayers( const QList<QgsMapLayer *> &layers )
   }
 
   emit layersRemoved( layerIds );
+  if ( layerOrderHasChanged )
+    emit layerOrderChanged();
 }
 
 void QgsProject::removeMapLayer( const QString &layerId )
@@ -2151,6 +2182,20 @@ void QgsProject::reloadAllLayers()
   }
 }
 
+QList<QgsMapLayer *> QgsProject::layerOrder() const
+{
+  return _qgis_listQPointerToRaw( mLayerOrder );
+}
+
+void QgsProject::setLayerOrder( const QList<QgsMapLayer *> &order )
+{
+  if ( order == layerOrder() )
+    return;
+
+  mLayerOrder = _qgis_listRawToQPointer( order );
+  emit layerOrderChanged();
+}
+
 void QgsProject::onMapLayerDeleted( QObject *obj )
 {
   QString id = mMapLayers.key( static_cast<QgsMapLayer *>( obj ) );

src/core/qgsproject.h

@@ -38,6 +38,7 @@
 #include "qgsexpressioncontextgenerator.h"
 #include "qgscoordinatereferencesystem.h"
 #include "qgsprojectproperty.h"
+#include "qgsmaplayer.h"
 
 class QFileInfo;
 class QDomDocument;
@@ -690,6 +691,22 @@ class CORE_EXPORT QgsProject : public QObject, public QgsExpressionContextGenera
      */
     void reloadAllLayers();
 
+    /**
+     * Returns an ordered list of layers. This list reflects the order of layers as
+     * drawn in the main map canvas for the project.
+     * @note added in QGIS 3.0
+     * @see setLayerOrder()
+     */
+    QList< QgsMapLayer * > layerOrder() const;
+
+    /**
+     * Sets the \a order for layers in the project. This list reflects the order of layers shown in
+     * the layer tree for the project.
+     * @note added in QGIS 3.0
+     * @see layerOrder()
+     */
+    void setLayerOrder( const QList< QgsMapLayer * > &order );
+
   signals:
     //! emitted when project is being read
     void readProject( const QDomDocument & );
@@ -892,6 +909,13 @@ class CORE_EXPORT QgsProject : public QObject, public QgsExpressionContextGenera
      */
     void legendLayersAdded( const QList<QgsMapLayer *> &layers );
 
+    /**
+     * Emitted when the order of layers in the project is changed.
+     * @note added in QGIS 3.0
+     * @see setLayerOrder()
+     */
+    void layerOrderChanged();
+
   public slots:
 
     /**
@@ -951,6 +975,8 @@ class CORE_EXPORT QgsProject : public QObject, public QgsExpressionContextGenera
 
     QMap<QString, QgsMapLayer *> mMapLayers;
 
+    QgsWeakMapLayerPointerList mLayerOrder;
+
     QString mErrorMessage;
 
     QgsProjectBadLayerHandler *mBadLayerHandler = nullptr;

src/gui/layertree/qgslayertreemapcanvasbridge.cpp

@@ -140,6 +140,7 @@ void QgsLayerTreeMapCanvasBridge::setCanvasLayers()
   int currentLayerCount = layerNodes.count();
   bool firstLayers = mAutoSetupOnFirstLayer && mLastLayerCount == 0 && currentLayerCount != 0;
 
+  QgsProject::instance()->setLayerOrder( canvasLayers );
   mCanvas->setLayers( canvasLayers );
   if ( mOverviewCanvas )
     mOverviewCanvas->setLayers( overviewLayers );

tests/src/python/test_qgsproject.py

@@ -18,12 +18,19 @@ import os
 
 import qgis  # NOQA
 
-from qgis.core import QgsProject, QgsApplication, QgsUnitTypes, QgsCoordinateReferenceSystem
-
+from qgis.core import (QgsProject,
+                       QgsApplication,
+                       QgsUnitTypes,
+                       QgsCoordinateReferenceSystem,
+                       QgsVectorLayer)
+from qgis.gui import (QgsLayerTreeMapCanvasBridge,
+                      QgsMapCanvas)
 from qgis.testing import start_app, unittest
 from utilities import (unitTestDataPath)
+from qgis.PyQt.QtCore import QDir
+from qgis.PyQt.QtTest import QSignalSpy
 
-start_app()
+app = start_app()
 TEST_DATA_DIR = unitTestDataPath()
 
 
@@ -176,6 +183,85 @@ class TestQgsProject(unittest.TestCase):
         expected = ['polys', 'lines']
         self.assertEqual(sorted(layers_names), sorted(expected))
 
+    def testLayerOrder(self):
+        """ test project layer order"""
+        prj = QgsProject()
+        layer = QgsVectorLayer("Point?field=fldtxt:string",
+                               "layer1", "memory")
+        layer2 = QgsVectorLayer("Point?field=fldtxt:string",
+                                "layer2", "memory")
+        layer3 = QgsVectorLayer("Point?field=fldtxt:string",
+                                "layer3", "memory")
+        prj.addMapLayers([layer, layer2, layer3])
+
+        layer_order_changed_spy = QSignalSpy(prj.layerOrderChanged)
+        prj.setLayerOrder([layer2, layer])
+        self.assertEqual(len(layer_order_changed_spy), 1)
+        prj.setLayerOrder([layer2, layer])
+        self.assertEqual(len(layer_order_changed_spy), 1) # no signal, order not changed
+
+        self.assertEqual(prj.layerOrder(), [layer2, layer])
+        prj.setLayerOrder([layer])
+        self.assertEqual(prj.layerOrder(), [layer])
+        self.assertEqual(len(layer_order_changed_spy), 2)
+
+        # remove a layer
+        prj.setLayerOrder([layer2, layer, layer3])
+        self.assertEqual(len(layer_order_changed_spy), 3)
+        prj.removeMapLayer(layer)
+        self.assertEqual(prj.layerOrder(), [layer2, layer3])
+        self.assertEqual(len(layer_order_changed_spy), 4)
+
+        # save and restore
+        file_name = os.path.join(str(QDir.tempPath()), 'proj.qgs')
+        prj.setFileName(file_name)
+        prj.write()
+        prj2 = QgsProject()
+        prj2.setFileName(file_name)
+        prj2.read()
+        self.assertEqual([l.id() for l in prj2.layerOrder()], [layer2.id(), layer3.id()])
+
+        # clear project
+        prj.clear()
+        self.assertEqual(prj.layerOrder(), [])
+
+    def testLayerOrderUpdatedThroughBridge(self):
+        """ test that project layer order is updated when layer tree changes """
+
+        prj = QgsProject.instance()
+        layer = QgsVectorLayer("Point?field=fldtxt:string",
+                               "layer1", "memory")
+        layer2 = QgsVectorLayer("Point?field=fldtxt:string",
+                                "layer2", "memory")
+        layer3 = QgsVectorLayer("Point?field=fldtxt:string",
+                                "layer3", "memory")
+        prj.addMapLayers([layer, layer2, layer3])
+
+        canvas = QgsMapCanvas()
+        bridge = QgsLayerTreeMapCanvasBridge(prj.layerTreeRoot(), canvas)
+
+        #custom layer order
+        bridge.setHasCustomLayerOrder(True)
+        bridge.setCustomLayerOrder([layer3.id(), layer.id(), layer2.id()])
+        app.processEvents()
+        self.assertEqual([l.id() for l in prj.layerOrder()], [layer3.id(), layer.id(), layer2.id()])
+
+        # no custom layer order
+        bridge.setHasCustomLayerOrder(False)
+        app.processEvents()
+        self.assertEqual([l.id() for l in prj.layerOrder()], [layer.id(), layer2.id(), layer3.id()])
+
+        # mess around with the layer tree order
+        root = prj.layerTreeRoot()
+        layer_node = root.findLayer(layer2.id())
+        cloned_node = layer_node.clone()
+        parent = layer_node.parent()
+        parent.insertChildNode(0, cloned_node)
+        parent.removeChildNode(layer_node)
+        app.processEvents()
+        # make sure project respects this
+        self.assertEqual([l.id() for l in prj.layerOrder()], [layer2.id(), layer.id(), layer3.id()])
+
 
 if __name__ == '__main__':
     unittest.main()