Make QgsXmlUtils handle storing/retrieving QgsProperty values

python/core/auto_generated/qgsxmlutils.sip.in

@@ -59,6 +59,7 @@ Supported types are
 - QVariant.Int
 - QVariant.Double
 - QVariant.String
+- :py:class:`QgsProperty` (since QGIS 3.4)
 %End
 
     static QVariant readVariant( const QDomElement &element );

src/core/qgsapplication.cpp

@@ -164,6 +164,7 @@ void QgsApplication::init( QString profileFolder )
   qRegisterMetaType<QgsUnitTypes::LayoutUnit>( "QgsUnitTypes::LayoutUnit" );
   qRegisterMetaType<QgsFeatureId>( "QgsFeatureId" );
   qRegisterMetaType<QgsFeatureIds>( "QgsFeatureIds" );
+  qRegisterMetaType<QgsProperty>( "QgsProperty" );
   qRegisterMetaType<Qgis::MessageLevel>( "Qgis::MessageLevel" );
   qRegisterMetaType<QgsReferencedRectangle>( "QgsReferencedRectangle" );
   qRegisterMetaType<QgsReferencedPointXY>( "QgsReferencedPointXY" );

src/core/qgsxmlutils.cpp

@@ -18,7 +18,7 @@
 
 #include "qgslogger.h"
 #include "qgsrectangle.h"
-
+#include "qgsproperty.h"
 
 QgsUnitTypes::DistanceUnit QgsXmlUtils::readMapUnits( const QDomElement &element )
 {
@@ -153,6 +153,18 @@ QDomElement QgsXmlUtils::writeVariant( const QVariant &value, QDomDocument &doc
       element.setAttribute( QStringLiteral( "value" ), value.toString() );
       break;
 
+    case QVariant::UserType:
+    {
+      if ( value.canConvert< QgsProperty >() )
+      {
+        element.setAttribute( QStringLiteral( "type" ), QStringLiteral( "QgsProperty" ) );
+        const QDomElement propertyElem = QgsXmlUtils::writeVariant( value.value< QgsProperty >().toVariant(), doc );
+        element.appendChild( propertyElem );
+        break;
+      }
+      FALLTHROUGH
+    }
+
     default:
       element.setAttribute( QStringLiteral( "type" ), QStringLiteral( "Unknown" ) );
       element.setAttribute( QStringLiteral( "value" ), value.toString() );
@@ -217,6 +229,18 @@ QVariant QgsXmlUtils::readVariant( const QDomElement &element )
     }
     return list;
   }
+  else if ( type == QLatin1String( "QgsProperty" ) )
+  {
+    const QDomNodeList values = element.childNodes();
+    if ( values.isEmpty() )
+      return QVariant();
+
+    QgsProperty p;
+    if ( p.loadVariant( QgsXmlUtils::readVariant( values.at( 0 ).toElement() ) ) )
+      return p;
+
+    return QVariant();
+  }
   else
   {
     return QVariant();

src/core/qgsxmlutils.h

@@ -66,7 +66,7 @@ class CORE_EXPORT QgsXmlUtils
      * - QVariant::Int
      * - QVariant::Double
      * - QVariant::String
-     *
+     * - QgsProperty (since QGIS 3.4)
      */
     static QDomElement writeVariant( const QVariant &value, QDomDocument &doc );
 

tests/src/python/test_qgsxmlutils.py

@@ -14,7 +14,8 @@
 
 import qgis  # NOQA switch sip api
 
-from qgis.core import QgsXmlUtils
+from qgis.core import (QgsXmlUtils,
+                       QgsProperty)
 
 from qgis.PyQt.QtXml import QDomDocument
 
@@ -102,6 +103,33 @@ def test_complex(self):
 
         self.assertEqual(my_properties, prop2)
 
+    def test_property(self):
+        """
+        Test that QgsProperty values are correctly loaded and written
+        """
+        doc = QDomDocument("properties")
+
+        prop = QgsProperty.fromValue(1001)
+        elem = QgsXmlUtils.writeVariant(prop, doc)
+
+        prop2 = QgsXmlUtils.readVariant(elem)
+
+        self.assertEqual(prop, prop2)
+
+        prop = QgsProperty.fromExpression('1+2=5')
+        elem = QgsXmlUtils.writeVariant(prop, doc)
+
+        prop2 = QgsXmlUtils.readVariant(elem)
+
+        self.assertEqual(prop, prop2)
+
+        prop = QgsProperty.fromField('oid')
+        elem = QgsXmlUtils.writeVariant(prop, doc)
+
+        prop2 = QgsXmlUtils.readVariant(elem)
+
+        self.assertEqual(prop, prop2)
+
 
 if __name__ == '__main__':
     unittest.main()