Don't reset mesh layer styling when changing data source for layer

python/core/auto_generated/mesh/qgsmeshlayer.sip.in

@@ -94,6 +94,8 @@ Constructor for LayerOptions with optional ``transformContext``.
 
       QgsCoordinateTransformContext transformContext;
 
+      bool loadDefaultStyle;
+
       bool skipCrsValidation;
     };
 
@@ -161,6 +163,8 @@ QgsMeshLayer cannot be copied.
 
     virtual bool supportsEditing() const;
 
+    virtual QString loadDefaultStyle( bool &resultFlag /Out/ ) ${SIP_FINAL};
+
 
     QString providerType() const;
 %Docstring

python/core/auto_generated/mesh/qgsmeshlayertemporalproperties.sip.in

@@ -89,6 +89,22 @@ Returns the method used to match dataset from temporal capabilities
 Sets the method used to match dataset from temporal capabilities
 
 :param matchingMethod: the matching method
+%End
+
+    bool isValid() const;
+%Docstring
+Returns whether the instance is valid
+
+.. versionadded:: 3.22
+%End
+
+    void setIsValid( bool isValid );
+%Docstring
+Sets whether the instance is valid
+
+:param isValid: whether the instance is valid
+
+.. versionadded:: 3.22
 %End
 
 };

python/core/auto_generated/mesh/qgsmeshrenderersettings.sip.in

@@ -747,6 +747,13 @@ Returns the active vector dataset group
 Sets the active vector dataset group
 
 .. versionadded:: 3.14
+%End
+
+    bool hasSettings( int datasetGroupIndex ) const;
+%Docstring
+Returns whether the group with ``index`` has render settings (scalar or vector)
+
+.. versionadded:: 3.22
 %End
 
 };

src/app/qgsapplayertreeviewmenuprovider.cpp

@@ -50,6 +50,7 @@
 #include "qgsvectorlayer.h"
 #include "qgsvectorlayerlabeling.h"
 #include "qgsxmlutils.h"
+#include "qgsmeshlayer.h"
 
 
 QgsAppLayerTreeViewMenuProvider::QgsAppLayerTreeViewMenuProvider( QgsLayerTreeView *view, QgsMapCanvas *canvas )
@@ -153,6 +154,7 @@ QMenu *QgsAppLayerTreeViewMenuProvider::createContextMenu()
       QgsRasterLayer *rlayer = qobject_cast<QgsRasterLayer *>( layer );
       QgsVectorLayer *vlayer = qobject_cast<QgsVectorLayer *>( layer );
       QgsPointCloudLayer *pcLayer = qobject_cast<QgsPointCloudLayer * >( layer );
+      QgsMeshLayer *meshLayer = qobject_cast<QgsMeshLayer * >( layer );
 
       if ( layer && layer->isSpatial() )
       {
@@ -363,8 +365,8 @@ QMenu *QgsAppLayerTreeViewMenuProvider::createContextMenu()
         menu->addAction( tr( "&Filter…" ), QgisApp::instance(), qOverload<>( &QgisApp::layerSubsetString ) );
       }
 
-      // change data source is only supported for vectors and rasters, point clouds
-      if ( vlayer || rlayer || pcLayer )
+      // change data source is only supported for vectors, rasters, point clouds, mesh
+      if ( vlayer || rlayer || pcLayer || meshLayer )
       {
 
         QAction *a = new QAction( layer->isValid() ? tr( "C&hange Data Source…" ) : tr( "Repair Data Source…" ), menu );

src/core/mesh/qgsmeshdatasetgroupstore.cpp

@@ -343,6 +343,16 @@ void QgsMeshDatasetGroupStore::readXml( const QDomElement &storeElem, const QgsR
     setDatasetGroupTreeItem( new QgsMeshDatasetGroupTreeItem( rootTreeItemElem, context ) );
 }
 
+int QgsMeshDatasetGroupStore::globalDatasetGroupIndexInSource( QgsMeshDatasetSourceInterface *source, int nativeGroupIndex ) const
+{
+  for ( QMap<int, DatasetGroup>::const_iterator it = mRegistery.cbegin(); it != mRegistery.cend(); ++it )
+  {
+    if ( it.value().first == source && it.value().second == nativeGroupIndex )
+      return it.key();
+  }
+
+  return -1;
+}
 
 bool QgsMeshDatasetGroupStore::saveDatasetGroup( QString filePath, int groupIndex, QString driver )
 {

src/core/mesh/qgsmeshdatasetgroupstore.h

@@ -210,6 +210,14 @@ class QgsMeshDatasetGroupStore: public QObject
     //! Reads the store's information from a DOM document
     void readXml( const QDomElement &storeElem, const QgsReadWriteContext &context );
 
+    /**
+     * Returns the global dataset group index of the dataset group with native index \a globalGroupIndex in the \a source
+     * Returns -1 if the group or the source is not registered
+     *
+     * Since QGIS 3.22
+     */
+    int globalDatasetGroupIndexInSource( QgsMeshDatasetSourceInterface *source, int nativeGroupIndex ) const;
+
   signals:
     //! Emitted after dataset groups are added
     void datasetGroupsAdded( QList<int> indexes );

src/core/mesh/qgsmeshlayer.cpp

@@ -51,12 +51,15 @@ QgsMeshLayer::QgsMeshLayer( const QString &meshLayerPath,
   : QgsMapLayer( QgsMapLayerType::MeshLayer, baseName, meshLayerPath ),
     mDatasetGroupStore( new QgsMeshDatasetGroupStore( this ) ),
     mTemporalProperties( new QgsMeshLayerTemporalProperties( this ) )
-
 {
   mShouldValidateCrs = !options.skipCrsValidation;
 
   const QgsDataProvider::ProviderOptions providerOptions { options.transformContext };
   QgsDataProvider::ReadFlags flags = QgsDataProvider::ReadFlags();
+  if ( options.loadDefaultStyle )
+  {
+    flags |= QgsDataProvider::FlagLoadDefaultStyle;
+  }
   if ( mReadFlags & QgsMapLayer::FlagTrustLayerMetadata )
   {
     flags |= QgsDataProvider::FlagTrustDataSource;
@@ -65,7 +68,7 @@ QgsMeshLayer::QgsMeshLayer( const QString &meshLayerPath,
   resetDatasetGroupTreeItem();
   setLegend( QgsMapLayerLegend::defaultMeshLegend( this ) );
 
-  if ( isValid() )
+  if ( isValid() && options.loadDefaultStyle )
     setDefaultRendererSettings( mDatasetGroupStore->datasetGroupIndexes() );
 
   connect( mDatasetGroupStore.get(), &QgsMeshDatasetGroupStore::datasetGroupsAdded, this, &QgsMeshLayer::onDatasetGroupsAdded );
@@ -201,6 +204,22 @@ bool QgsMeshLayer::supportsEditing() const
   return driverMetadata.capabilities() & QgsMeshDriverMetadata::CanWriteMeshData;
 }
 
+QString QgsMeshLayer::loadDefaultStyle( bool &resultFlag )
+{
+  const QList<int> groupsList = datasetGroupsIndexes();
+
+  for ( const int index : groupsList )
+    assignDefaultStyleToDatasetGroup( index );
+
+  if ( !groupsList.isEmpty() )
+  {
+    emit rendererChanged();
+    emitStyleChanged();
+  }
+
+  return QgsMapLayer::loadDefaultStyle( resultFlag );
+}
+
 bool QgsMeshLayer::addDatasets( const QString &path, const QDateTime &defaultReferenceTime )
 {
   const bool isTemporalBefore = dataProvider()->temporalCapabilities()->hasTemporalCapabilities();
@@ -1138,17 +1157,8 @@ void QgsMeshLayer::setDataSourcePrivate( const QString &dataSource, const QStrin
   mLayerName = baseName;
   setProviderType( provider );
 
-  // if we’re given a provider type, try to create and bind one to this layer
-  bool ok = false;
   if ( !mDataSource.isEmpty() && !provider.isEmpty() )
-  {
-    ok = setDataProvider( provider, options, flags );
-  }
-
-  if ( ok )
-  {
-    mTemporalProperties->setDefaultsFromDataProviderTemporalCapabilities( mDataProvider->temporalCapabilities() );
-  }
+    setDataProvider( provider, options, flags );
 }
 
 QgsPointXY QgsMeshLayer::snapOnElement( QgsMesh::ElementType elementType, const QgsPointXY &point, double searchRadius )
@@ -1693,8 +1703,15 @@ bool QgsMeshLayer::setDataProvider( QString const &provider, const QgsDataProvid
     return false;
   }
 
+  if ( !mTemporalProperties->isValid() )
+  {
+    mTemporalProperties->setDefaultsFromDataProviderTemporalCapabilities( dataProvider()->temporalCapabilities() );
+  }
+
   mDataProvider->setTemporalUnit( mTemporalUnit );
+
   mDatasetGroupStore->setPersistentProvider( mDataProvider, mExtraDatasetUri );
+
   setCrs( mDataProvider->crs() );
 
   if ( provider == QLatin1String( "mesh_memory" ) )
@@ -1703,8 +1720,17 @@ bool QgsMeshLayer::setDataProvider( QString const &provider, const QgsDataProvid
     mDataSource = mDataSource + QStringLiteral( "&uid=%1" ).arg( QUuid::createUuid().toString() );
   }
 
+  // set default style if required by flags or if the dataset group does not has a style yet
   for ( int i = 0; i < mDataProvider->datasetGroupCount(); ++i )
-    assignDefaultStyleToDatasetGroup( i );
+  {
+    int globalIndex = mDatasetGroupStore->globalDatasetGroupIndexInSource( mDataProvider, i );
+    if ( globalIndex != -1 &&
+         ( !mRendererSettings.hasSettings( globalIndex ) || ( flags & QgsDataProvider::FlagLoadDefaultStyle ) ) )
+      assignDefaultStyleToDatasetGroup( globalIndex );
+  }
+
+  emit rendererChanged();
+  emitStyleChanged();
 
   connect( mDataProvider, &QgsMeshDataProvider::dataChanged, this, &QgsMeshLayer::dataChanged );
 

src/core/mesh/qgsmeshlayer.h

@@ -112,8 +112,17 @@ class CORE_EXPORT QgsMeshLayer : public QgsMapLayer
         : transformContext( transformContext )
       {}
 
+      /**
+       * Coordinate transform context
+       */
       QgsCoordinateTransformContext transformContext;
 
+      /**
+       * Set to TRUE if the default layer style should be loaded.
+       * \since QGIS 3.22
+       */
+      bool loadDefaultStyle = true;
+
       /**
        * Controls whether the layer is allowed to have an invalid/unknown CRS.
        *
@@ -182,6 +191,7 @@ class CORE_EXPORT QgsMeshLayer : public QgsMapLayer
     QString htmlMetadata() const override;
     bool isEditable() const override;
     bool supportsEditing() const override;
+    QString loadDefaultStyle( bool &resultFlag SIP_OUT ) FINAL;
 
     //! Returns the provider type for this layer
     QString providerType() const;

src/core/mesh/qgsmeshlayertemporalproperties.cpp

@@ -61,6 +61,7 @@ bool QgsMeshLayerTemporalProperties::readXml( const QDomElement &element, const
   mMatchingMethod = static_cast<QgsMeshDataProviderTemporalCapabilities::MatchingTemporalDatasetMethod>(
                       temporalElement.attribute( QStringLiteral( "matching-method" ) ).toInt() );
 
+  mIsValid = true;
   return true;
 }
 
@@ -74,6 +75,8 @@ void QgsMeshLayerTemporalProperties::setDefaultsFromDataProviderTemporalCapabili
 
   if ( mReferenceTime.isValid() )
     mTimeExtent = temporalCapabilities->timeExtent();
+
+  mIsValid = true;
 }
 
 QgsDateTimeRange QgsMeshLayerTemporalProperties::calculateTemporalExtent( QgsMapLayer * ) const
@@ -112,3 +115,13 @@ void QgsMeshLayerTemporalProperties::setMatchingMethod( const QgsMeshDataProvide
 {
   mMatchingMethod = matchingMethod;
 }
+
+bool QgsMeshLayerTemporalProperties::isValid() const
+{
+  return mIsValid;
+}
+
+void QgsMeshLayerTemporalProperties::setIsValid( bool isValid )
+{
+  mIsValid = isValid;
+}

src/core/mesh/qgsmeshlayertemporalproperties.h

@@ -100,11 +100,28 @@ class CORE_EXPORT QgsMeshLayerTemporalProperties : public QgsMapLayerTemporalPro
      */
     void setMatchingMethod( const QgsMeshDataProviderTemporalCapabilities::MatchingTemporalDatasetMethod &matchingMethod );
 
+    /**
+     * Returns whether the instance is valid
+     *
+     * \since QGIS 3.22
+     */
+    bool isValid() const;
+
+    /**
+     * Sets whether the instance is valid
+     *
+     * \param isValid whether the instance is valid
+     *
+     * \since QGIS 3.22
+     */
+    void setIsValid( bool isValid );
+
   private:
     QDateTime mReferenceTime;
     QgsDateTimeRange mTimeExtent;
     QgsMeshDataProviderTemporalCapabilities::MatchingTemporalDatasetMethod mMatchingMethod =
       QgsMeshDataProviderTemporalCapabilities::FindClosestDatasetBeforeStartRangeTime;
+    bool mIsValid = false;
 };
 
 #endif // QGSMESHLAYERTEMPORALPROPERTIES_H

src/core/mesh/qgsmeshrenderersettings.cpp

@@ -740,3 +740,7 @@ void QgsMeshRendererVectorTracesSettings::setParticlesCount( int value )
   mParticlesCount = value;
 }
 
+bool QgsMeshRendererSettings::hasSettings( int datasetGroupIndex ) const
+{
+  return mRendererScalarSettings.contains( datasetGroupIndex ) || mRendererVectorSettings.contains( datasetGroupIndex );
+}

src/core/mesh/qgsmeshrenderersettings.h

@@ -673,6 +673,13 @@ class CORE_EXPORT QgsMeshRendererSettings
      */
     void setActiveVectorDatasetGroup( int activeVectorDatasetGroup );
 
+    /**
+    * Returns whether the group with \a index has render settings (scalar or vector)
+    *
+    * \since QGIS 3.22
+    */
+    bool hasSettings( int datasetGroupIndex ) const;
+
   private:
     QgsMeshRendererMeshSettings mRendererNativeMeshSettings;
     QgsMeshRendererMeshSettings mRendererTriangularMeshSettings;

src/core/qgsmaplayerfactory.cpp

@@ -91,6 +91,7 @@ QgsMapLayer *QgsMapLayerFactory::createLayer( const QString &uri, const QString
     {
       QgsMeshLayer::LayerOptions meshOptions;
       meshOptions.transformContext = options.transformContext;
+      meshOptions.loadDefaultStyle = options.loadDefaultStyle;
       return new QgsMeshLayer( uri, name, provider, meshOptions );
     }