Added default feature title format when display expression is empty (#3735)

* Added default feature title format when display expression is empty

* handling empty layer name

* Unnamed Layer translatable

---------

Co-authored-by: VitorVieiraZ <vmvieira8@outlook.com>

Author: tomasMizera

app/attributes/attributepreviewcontroller.cpp

@@ -135,7 +135,25 @@ QString AttributePreviewController::featureTitle( )
   QgsExpressionContext context( globalProjectLayerScopes( mFeatureLayerPair.layer() ) );
   context.setFeature( mFeatureLayerPair.feature() );
   QgsExpression expr( mFeatureLayerPair.layer()->displayExpression() );
-  return expr.evaluate( &context ).toString();
+
+  QString title = expr.evaluate( &context ).toString();
+
+  if ( title.isEmpty() )
+  {
+    // let's use a default format with layer name as user did not set any specific display expression
+    if ( mFeatureLayerPair.layer() && mFeatureLayerPair.layer()->isValid() && mFeatureLayerPair.feature().isValid() )
+    {
+      QString layerName = mFeatureLayerPair.layer()->name();
+      if ( layerName.isEmpty() )
+      {
+        layerName = tr( "Unnamed Layer" );
+      }
+
+      title = QStringLiteral( "%1 (%2)" ).arg( layerName ).arg( mFeatureLayerPair.feature().id() );
+    }
+  }
+
+  return title;
 }
 
 QList<QgsExpressionContextScope *> AttributePreviewController::globalProjectLayerScopes( QgsMapLayer *layer )

app/test/testattributepreviewcontroller.cpp

@@ -201,3 +201,64 @@ void TestAttributePreviewController::testPreviewForms()
   // Cleanup
   QgsProject::instance()->removeAllMapLayers();
 }
+
+void TestAttributePreviewController::testFeatureTitle()
+{
+  // Layer creation
+  QgsVectorLayer *layer =
+    new QgsVectorLayer( QStringLiteral( "Point?field=name:string" ),
+                        QStringLiteral( "layer" ),
+                        QStringLiteral( "memory" )
+                      );
+  QVERIFY( layer && layer->isValid() );
+
+  layer->setName( QStringLiteral( "Point" ) );
+
+  QgsFeature f1( layer->dataProvider()->fields() );
+  f1.setAttribute( QStringLiteral( "name" ), "My feature" );
+  layer->dataProvider()->addFeatures( QgsFeatureList() << f1 );
+
+  QgsFeature f2( layer->dataProvider()->fields() );
+  f2.setAttribute( QStringLiteral( "name" ), "" );
+  layer->dataProvider()->addFeatures( QgsFeatureList() << f2 );
+
+  QgsProject::instance()->addMapLayer( layer );
+
+  AttributePreviewController controller;
+  controller.setProject( QgsProject::instance() );
+
+  //
+  // Valid scenarios
+  //
+
+  FeatureLayerPair pair1( layer->getFeature( 1 ), layer );
+  controller.setFeatureLayerPair( pair1 );
+  QCOMPARE( controller.title(), QStringLiteral( "My feature" ) );
+
+  FeatureLayerPair pair2( layer->getFeature( 2 ), layer );
+  controller.setFeatureLayerPair( pair2 );
+  QCOMPARE( controller.title(), QStringLiteral( "Point (2)" ) );
+
+  //
+  // FeaturePair is somehow malformed
+  //
+
+  FeatureLayerPair pair3( QgsFeature(), nullptr );
+  controller.setFeatureLayerPair( pair3 );
+  QCOMPARE( controller.title(), QStringLiteral( "" ) );
+
+  FeatureLayerPair pair4( layer->getFeature( 2 ), nullptr );
+  controller.setFeatureLayerPair( pair4 );
+  QCOMPARE( controller.title(), QStringLiteral( "" ) );
+
+  FeatureLayerPair pair5( QgsFeature(), layer );
+  controller.setFeatureLayerPair( pair5 );
+  QCOMPARE( controller.title(), QStringLiteral( "" ) );
+
+  //
+  // Set layer name as empty and check if default "Unnamed Layer" is applied
+  //
+  layer->setName( QStringLiteral( "" ) );
+  controller.setFeatureLayerPair( pair2 );
+  QCOMPARE( controller.title(), QStringLiteral( "Unnamed Layer (2)" ) );
+}

app/test/testattributepreviewcontroller.h

@@ -30,6 +30,7 @@ class TestAttributePreviewController: public QObject
 
     void testPreviewForms();
     void testMultilineMapTips();
+    void testFeatureTitle();
 
   private:
 };