[composer] Update features if atlas preview enabled and coverage filter/sort changes.

Protect against atlas with no matching features

Author: nyalldawson

src/app/composer/qgsatlascompositionwidget.cpp

@@ -136,7 +136,7 @@ void QgsAtlasCompositionWidget::onLayerAdded( QgsMapLayer* map )
     if ( mAtlasCoverageLayerComboBox->count() == 1 )
     {
       atlasMap->setCoverageLayer( vectorLayer );
-      atlasMap->updateFeatures();
+      updateAtlasFeatures();
       checkLayerType( vectorLayer );
     }
   }
@@ -192,7 +192,7 @@ void QgsAtlasCompositionWidget::on_mAtlasCoverageLayerComboBox_currentIndexChang
     {
       checkLayerType( layer );
       atlasMap->setCoverageLayer( layer );
-      atlasMap->updateFeatures();
+      updateAtlasFeatures();
     }
 
     // update sorting columns
@@ -335,7 +335,36 @@ void QgsAtlasCompositionWidget::on_mAtlasSortFeatureCheckBox_stateChanged( int s
     mAtlasSortFeatureKeyComboBox->setEnabled( false );
   }
   atlasMap->setSortFeatures( state == Qt::Checked );
-  atlasMap->updateFeatures();
+  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 )
@@ -350,7 +379,7 @@ void QgsAtlasCompositionWidget::on_mAtlasSortFeatureKeyComboBox_currentIndexChan
   {
     atlasMap->setSortKeyAttributeIndex( index );
   }
-  atlasMap->updateFeatures();
+  updateAtlasFeatures();
 }
 
 void QgsAtlasCompositionWidget::on_mAtlasFeatureFilterCheckBox_stateChanged( int state )
@@ -372,7 +401,7 @@ void QgsAtlasCompositionWidget::on_mAtlasFeatureFilterCheckBox_stateChanged( int
     mAtlasFeatureFilterButton->setEnabled( false );
   }
   atlasMap->setFilterFeatures( state == Qt::Checked );
-  atlasMap->updateFeatures();
+  updateAtlasFeatures();
 }
 
 void QgsAtlasCompositionWidget::on_mAtlasFeatureFilterEdit_textChanged( const QString& text )
@@ -384,7 +413,7 @@ void QgsAtlasCompositionWidget::on_mAtlasFeatureFilterEdit_textChanged( const QS
   }
 
   atlasMap->setFeatureFilter( text );
-  atlasMap->updateFeatures();
+  updateAtlasFeatures();
 }
 
 void QgsAtlasCompositionWidget::on_mAtlasFeatureFilterButton_clicked()
@@ -421,7 +450,7 @@ void QgsAtlasCompositionWidget::on_mAtlasSortFeatureDirectionButton_clicked()
   }
 
   atlasMap->setSortAscending( at == Qt::UpArrow );
-  atlasMap->updateFeatures();
+  updateAtlasFeatures();
 }
 
 void QgsAtlasCompositionWidget::fillSortColumns()

src/app/composer/qgsatlascompositionwidget.h

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

src/app/composer/qgscomposer.cpp

@@ -807,7 +807,21 @@ void QgsComposer::on_mActionAtlasPreview_triggered( bool checked )
   mActionAtlasNext->setEnabled( checked );
   mActionAtlasPrev->setEnabled( checked );
 
-  mComposition->setAtlasPreviewEnabled( checked );
+  bool previewEnabled = mComposition->setAtlasPreviewEnabled( checked );
+  if ( !previewEnabled )
+  {
+    //something went wrong, eg, no matching features
+    QMessageBox::warning( 0, tr( "Enable atlas preview" ),
+                          tr( "No matching atlas features found!" ),
+                          QMessageBox::Ok,
+                          QMessageBox::Ok );
+    mActionAtlasPreview->blockSignals( true );
+    mActionAtlasPreview->setChecked( false );
+    mActionAtlasPreview->blockSignals( false );
+    mStatusAtlasLabel->setText( QString() );
+    return;
+  }
+
   if ( checked )
   {
     atlasMap->firstFeature();

src/core/composer/qgsatlascomposition.cpp

@@ -100,13 +100,13 @@ class FieldSorter
     bool mAscending;
 };
 
-void QgsAtlasComposition::updateFeatures()
+int QgsAtlasComposition::updateFeatures()
 {
   //needs to be called when layer, filter, sort changes
 
   if ( !mComposerMap || !mCoverageLayer )
   {
-    return;
+    return 0;
   }
 
   const QgsCoordinateReferenceSystem& coverage_crs = mCoverageLayer->crs();
@@ -135,7 +135,7 @@ void QgsAtlasComposition::updateFeatures()
   QgsFeatureIterator fit = mCoverageLayer->getFeatures();
 
   std::auto_ptr<QgsExpression> filterExpression;
-  if ( mFilterFeatures )
+  if ( mFilterFeatures && !mFeatureFilter.isEmpty() )
   {
     filterExpression = std::auto_ptr<QgsExpression>( new QgsExpression( mFeatureFilter ) );
     if ( filterExpression->hasParserError() )
@@ -151,7 +151,7 @@ void QgsAtlasComposition::updateFeatures()
   mFeatureKeys.clear();
   while ( fit.nextFeature( feat ) )
   {
-    if ( mFilterFeatures )
+    if ( mFilterFeatures && !mFeatureFilter.isEmpty() )
     {
       QVariant result = filterExpression->evaluate( &feat, mCoverageLayer->pendingFields() );
       if ( filterExpression->hasEvalError() )
@@ -188,17 +188,24 @@ void QgsAtlasComposition::updateFeatures()
   {
     firstFeature();
   }
+
+  return mFeatureIds.size();
 }
 
 
-void QgsAtlasComposition::beginRender()
+bool QgsAtlasComposition::beginRender()
 {
   if ( !mComposerMap || !mCoverageLayer )
   {
-    return;
+    return false;
   }
 
-  updateFeatures();
+  bool featuresUpdated = updateFeatures();
+  if ( !featuresUpdated )
+  {
+    //no matching features found
+    return false;
+  }
 
   mRestoreLayer = false;
   QStringList& layerSet = mComposition->mapRenderer()->layerSet();
@@ -216,6 +223,8 @@ void QgsAtlasComposition::beginRender()
   // special columns for expressions
   QgsExpression::setSpecialColumn( "$numpages", QVariant( mComposition->numPages() ) );
   QgsExpression::setSpecialColumn( "$numfeatures", QVariant(( int )mFeatureIds.size() ) );
+
+  return true;
 }
 
 void QgsAtlasComposition::endRender()

src/core/composer/qgsatlascomposition.h

@@ -81,8 +81,9 @@ class CORE_EXPORT QgsAtlasComposition : public QObject
     int sortKeyAttributeIndex() const { return mSortKeyAttributeIdx; }
     void setSortKeyAttributeIndex( int idx ) { mSortKeyAttributeIdx = idx; }
 
-    /** Begins the rendering. */
-    void beginRender();
+    /** Begins the rendering. Returns true if successful, false if no matching atlas
+      features found.*/
+    bool beginRender();
     /** Ends the rendering. Restores original extent */
     void endRender();
 
@@ -100,7 +101,9 @@ class CORE_EXPORT QgsAtlasComposition : public QObject
 
     QgsComposition* composition() { return mComposition; }
 
-    void updateFeatures();
+    /** Requeries the current atlas coverage layer and applies filtering and sorting. Returns
+      number of matching features. Must be called after prepareForFeature( i ) */
+    int updateFeatures();
 
     void nextFeature();
     void prevFeature();

src/core/composer/qgscomposition.cpp

@@ -2327,7 +2327,7 @@ void QgsComposition::computeWorldFileParameters( double& a, double& b, double& c
   f = r[3] * s[2] + r[4] * s[5] + r[5];
 }
 
-void QgsComposition::setAtlasPreviewEnabled( bool e )
+bool QgsComposition::setAtlasPreviewEnabled( bool e )
 {
   mAtlasPreviewEnabled = e;
 
@@ -2337,10 +2337,16 @@ void QgsComposition::setAtlasPreviewEnabled( bool e )
   }
   else
   {
-    mAtlasComposition.beginRender();
+    bool atlasHasFeatures = mAtlasComposition.beginRender();
+    if ( ! atlasHasFeatures )
+    {
+      mAtlasPreviewEnabled = false;
+      return false;
+    }
   }
 
   update();
+  return true;
 }
 
 void QgsComposition::relativeResizeRect( QRectF& rectToResize, const QRectF& boundsBefore, const QRectF& boundsAfter )

src/core/composer/qgscomposition.h

@@ -427,7 +427,8 @@ class CORE_EXPORT QgsComposition : public QGraphicsScene
 
     /** Is the atlas preview enabled ? */
     bool atlasPreviewEnabled() const { return mAtlasPreviewEnabled; }
-    void setAtlasPreviewEnabled( bool e );
+    /** Set atlas preview enabled. Returns false if atlas preview could not be enabled */
+    bool setAtlasPreviewEnabled( bool e );
 
 
   public slots: