src/app/composer/qgsatlascompositionwidget.cpp

@@ -136,6 +136,7 @@ void QgsAtlasCompositionWidget::onLayerAdded( QgsMapLayer* map )
     if ( mAtlasCoverageLayerComboBox->count() == 1 )
     {
       atlasMap->setCoverageLayer( vectorLayer );
+      updateAtlasFeatures();
       checkLayerType( vectorLayer );
     }
   }
@@ -191,6 +192,7 @@ void QgsAtlasCompositionWidget::on_mAtlasCoverageLayerComboBox_currentIndexChang
     {
       checkLayerType( layer );
       atlasMap->setCoverageLayer( layer );
+      updateAtlasFeatures();
     }
 
     // update sorting columns
@@ -333,6 +335,36 @@ void QgsAtlasCompositionWidget::on_mAtlasSortFeatureCheckBox_stateChanged( int s
     mAtlasSortFeatureKeyComboBox->setEnabled( false );
   }
   atlasMap->setSortFeatures( state == Qt::Checked );
+  updateAtlasFeatures();
+}
+
+void QgsAtlasCompositionWidget::updateAtlasFeatures()
+{
+  //only do this if composer mode is preview
+  if ( !mComposition->atlasPreviewEnabled() )
+  {
+    return;
+  }
+
+  //update atlas features
+  QgsAtlasComposition* atlasMap = &mComposition->atlasComposition();
+  if ( !atlasMap )
+  {
+    return;
+  }
+
+  bool updated = atlasMap->updateFeatures();
+  if ( !updated )
+  {
+    QMessageBox::warning( 0, tr( "Atlas preview" ),
+                          tr( "No matching atlas features found!" ),
+                          QMessageBox::Ok,
+                          QMessageBox::Ok );
+
+    //Perhaps atlas preview should be disabled now? If so, it may get annoying if user is editing
+    //the filter expression and it keeps disabling itself.
+    return;
+  }
 }
 
 void QgsAtlasCompositionWidget::on_mAtlasSortFeatureKeyComboBox_currentIndexChanged( int index )
@@ -347,6 +379,7 @@ void QgsAtlasCompositionWidget::on_mAtlasSortFeatureKeyComboBox_currentIndexChan
   {
     atlasMap->setSortKeyAttributeIndex( index );
   }
+  updateAtlasFeatures();
 }
 
 void QgsAtlasCompositionWidget::on_mAtlasFeatureFilterCheckBox_stateChanged( int state )
@@ -368,6 +401,7 @@ void QgsAtlasCompositionWidget::on_mAtlasFeatureFilterCheckBox_stateChanged( int
     mAtlasFeatureFilterButton->setEnabled( false );
   }
   atlasMap->setFilterFeatures( state == Qt::Checked );
+  updateAtlasFeatures();
 }
 
 void QgsAtlasCompositionWidget::on_mAtlasFeatureFilterEdit_textChanged( const QString& text )
@@ -379,6 +413,7 @@ void QgsAtlasCompositionWidget::on_mAtlasFeatureFilterEdit_textChanged( const QS
   }
 
   atlasMap->setFeatureFilter( text );
+  updateAtlasFeatures();
 }
 
 void QgsAtlasCompositionWidget::on_mAtlasFeatureFilterButton_clicked()
@@ -415,6 +450,7 @@ void QgsAtlasCompositionWidget::on_mAtlasSortFeatureDirectionButton_clicked()
   }
 
   atlasMap->setSortAscending( at == Qt::UpArrow );
+  updateAtlasFeatures();
 }
 
 void QgsAtlasCompositionWidget::fillSortColumns()

src/app/composer/qgsatlascompositionwidget.h

@@ -62,6 +62,8 @@ class QgsAtlasCompositionWidget:
 
     void updateGuiElements();
 
+    void updateAtlasFeatures();
+
   private:
     QgsComposition* mComposition;