Move method to evaluate a variant to a feature source to QgsProcessingUtils

python/core/processing/qgsprocessingutils.sip

@@ -79,6 +79,20 @@ class QgsProcessingUtils
  :rtype: QgsMapLayer
 %End
 
+    static QgsProcessingFeatureSource *variantToSource( const QVariant &value, QgsProcessingContext &context, const QVariant &fallbackValue = QVariant() ) /Factory/;
+%Docstring
+ Converts a variant ``value`` to a new feature source.
+
+ Sources will either be taken from ``context``'s active project, or loaded from external
+ sources and stored temporarily in the ``context``.
+
+ The optional ``fallbackValue`` can be used to specify a "default" value which is used
+ if ``value`` cannot be successfully converted to a source.
+
+ This function creates a new object and the caller takes responsibility for deleting the returned object.
+ :rtype: QgsProcessingFeatureSource
+%End
+
     static QString normalizeLayerSource( const QString &source );
 %Docstring
  Normalizes a layer ``source`` string for safe comparison across different

src/core/processing/qgsprocessingparameters.cpp

@@ -277,55 +277,7 @@ QgsProcessingFeatureSource *QgsProcessingParameters::parameterAsSource( const Qg
 
   QVariant val = parameters.value( definition->name() );
 
-  bool selectedFeaturesOnly = false;
+  return QgsProcessingUtils::variantToSource( val, context, definition->defaultValue() );
-  if ( val.canConvert<QgsProcessingFeatureSourceDefinition>() )
-  {
-    // input is a QgsProcessingFeatureSourceDefinition - get extra properties from it
-    QgsProcessingFeatureSourceDefinition fromVar = qvariant_cast<QgsProcessingFeatureSourceDefinition>( val );
-    selectedFeaturesOnly = fromVar.selectedFeaturesOnly;
-    val = fromVar.source;
-  }
-
-  if ( QgsVectorLayer *layer = qobject_cast< QgsVectorLayer * >( qvariant_cast<QObject *>( val ) ) )
-  {
-    return new QgsProcessingFeatureSource( layer, context );
-  }
-
-  QString layerRef;
-  if ( val.canConvert<QgsProperty>() )
-  {
-    layerRef = val.value< QgsProperty >().valueAsString( context.expressionContext(), definition->defaultValue().toString() );
-  }
-  else if ( !val.isValid() || val.toString().isEmpty() )
-  {
-    // fall back to default
-    if ( QgsVectorLayer *layer = qobject_cast< QgsVectorLayer * >( qvariant_cast<QObject *>( definition->defaultValue() ) ) )
-    {
-      return new QgsProcessingFeatureSource( layer, context );
-    }
-
-    layerRef = definition->defaultValue().toString();
-  }
-  else
-  {
-    layerRef = val.toString();
-  }
-
-  if ( layerRef.isEmpty() )
-    return nullptr;
-
-  QgsVectorLayer *vl = qobject_cast< QgsVectorLayer *>( QgsProcessingUtils::mapLayerFromString( layerRef, context ) );
-  if ( !vl )
-    return nullptr;
-
-  if ( selectedFeaturesOnly )
-  {
-    return new QgsProcessingFeatureSource( new QgsVectorLayerSelectedFeatureSource( vl ), context, true );
-  }
-  else
-  {
-    return new QgsProcessingFeatureSource( vl, context );
-  }
 }
 
 QString QgsProcessingParameters::parameterAsCompatibleSourceLayerPath( const QgsProcessingParameterDefinition *definition, const QVariantMap &parameters, QgsProcessingContext &context, const QStringList &compatibleFormats, const QString &preferredFormat, QgsProcessingFeedback *feedback )

src/core/processing/qgsprocessingutils.cpp

@@ -25,6 +25,7 @@
 #include "qgsmemoryproviderutils.h"
 #include "qgsprocessingparameters.h"
 #include "qgsprocessingalgorithm.h"
+#include "qgsvectorlayerfeatureiterator.h"
 
 QList<QgsRasterLayer *> QgsProcessingUtils::compatibleRasterLayers( QgsProject *project, bool sort )
 {
@@ -208,6 +209,60 @@ QgsMapLayer *QgsProcessingUtils::mapLayerFromString( const QString &string, QgsP
   }
 }
 
+QgsProcessingFeatureSource *QgsProcessingUtils::variantToSource( const QVariant &value, QgsProcessingContext &context, const QVariant &fallbackValue )
+{
+  QVariant val = value;
+  bool selectedFeaturesOnly = false;
+  if ( val.canConvert<QgsProcessingFeatureSourceDefinition>() )
+  {
+    // input is a QgsProcessingFeatureSourceDefinition - get extra properties from it
+    QgsProcessingFeatureSourceDefinition fromVar = qvariant_cast<QgsProcessingFeatureSourceDefinition>( val );
+    selectedFeaturesOnly = fromVar.selectedFeaturesOnly;
+    val = fromVar.source;
+  }
+
+  if ( QgsVectorLayer *layer = qobject_cast< QgsVectorLayer * >( qvariant_cast<QObject *>( val ) ) )
+  {
+    return new QgsProcessingFeatureSource( layer, context );
+  }
+
+  QString layerRef;
+  if ( val.canConvert<QgsProperty>() )
+  {
+    layerRef = val.value< QgsProperty >().valueAsString( context.expressionContext(), fallbackValue.toString() );
+  }
+  else if ( !val.isValid() || val.toString().isEmpty() )
+  {
+    // fall back to default
+    if ( QgsVectorLayer *layer = qobject_cast< QgsVectorLayer * >( qvariant_cast<QObject *>( fallbackValue ) ) )
+    {
+      return new QgsProcessingFeatureSource( layer, context );
+    }
+
+    layerRef = fallbackValue.toString();
+  }
+  else
+  {
+    layerRef = val.toString();
+  }
+
+  if ( layerRef.isEmpty() )
+    return nullptr;
+
+  QgsVectorLayer *vl = qobject_cast< QgsVectorLayer *>( QgsProcessingUtils::mapLayerFromString( layerRef, context ) );
+  if ( !vl )
+    return nullptr;
+
+  if ( selectedFeaturesOnly )
+  {
+    return new QgsProcessingFeatureSource( new QgsVectorLayerSelectedFeatureSource( vl ), context, true );
+  }
+  else
+  {
+    return new QgsProcessingFeatureSource( vl, context );
+  }
+}
+
 bool QgsProcessingUtils::canUseLayer( const QgsRasterLayer *layer )
 {
   // only gdal file-based layers

src/core/processing/qgsprocessingutils.h

@@ -29,6 +29,7 @@ class QgsProject;
 class QgsProcessingContext;
 class QgsMapLayerStore;
 class QgsProcessingFeedback;
+class QgsProcessingFeatureSource;
 
 #include <QString>
 #include <QVariant>
@@ -95,6 +96,19 @@ class CORE_EXPORT QgsProcessingUtils
      */
     static QgsMapLayer *mapLayerFromString( const QString &string, QgsProcessingContext &context, bool allowLoadingNewLayers = true );
 
+    /**
+     * Converts a variant \a value to a new feature source.
+     *
+     * Sources will either be taken from \a context's active project, or loaded from external
+     * sources and stored temporarily in the \a context.
+     *
+     * The optional \a fallbackValue can be used to specify a "default" value which is used
+     * if \a value cannot be successfully converted to a source.
+     *
+     * This function creates a new object and the caller takes responsibility for deleting the returned object.
+     */
+    static QgsProcessingFeatureSource *variantToSource( const QVariant &value, QgsProcessingContext &context, const QVariant &fallbackValue = QVariant() ) SIP_FACTORY;
+
     /**
      * Normalizes a layer \a source string for safe comparison across different
      * operating system environments.