[FIX #7543] Dual View Table/Form: Preview column not saved in project

src/core/qgsvectorlayer.cpp

@@ -1511,6 +1511,18 @@ bool QgsVectorLayer::readXml( const QDomNode& layer_node )
   updateFields();
   connect( QgsMapLayerRegistry::instance(), SIGNAL( layerWillBeRemoved( QString ) ), this, SLOT( checkJoinLayerRemove( QString ) ) );
 
+  QDomNode prevExpNode = layer_node.namedItem( "previewExpression" );
+
+  if( prevExpNode.isNull() )
+  {
+    mDisplayExpression = "";
+  }
+  else
+  {
+    QDomElement prevExpElem = prevExpNode.toElement();
+    mDisplayExpression = prevExpElem.text();
+  }
+
   QString errorMsg;
   if ( !readSymbology( layer_node, errorMsg ) )
   {
@@ -1658,6 +1670,12 @@ bool QgsVectorLayer::writeXml( QDomNode & layer_node,
     layer_node.appendChild( provider );
   }
 
+  // save preview expression
+  QDomElement prevExpElem = document.createElement( "previewExpression" );
+  QDomText prevExpText = document.createTextNode( mDisplayExpression );
+  prevExpElem.appendChild( prevExpText );
+  layer_node.appendChild( prevExpElem );
+
   //save joins
   mJoinBuffer->writeXml( layer_node, document );
 
@@ -2790,6 +2808,16 @@ const QString QgsVectorLayer::displayField() const
   return mDisplayField;
 }
 
+void QgsVectorLayer::setDisplayExpression( const QString displayExpression )
+{
+  mDisplayExpression = displayExpression;
+}
+
+const QString QgsVectorLayer::displayExpression()
+{
+  return mDisplayExpression;
+}
+
 bool QgsVectorLayer::isEditable() const
 {
   return ( mEditBuffer && mDataProvider );

src/core/qgsvectorlayer.h

@@ -257,6 +257,24 @@ class CORE_EXPORT QgsVectorLayer : public QgsMapLayer
     /** Returns the primary display field name used in the identify results dialog */
     const QString displayField() const;
 
+    /** Set the preview expression, used to create a human readable preview string.
+     *  Used e.g. in the attribute table feature list. Uses @link {QgsExpression}.
+     *
+     *  @param previewExpression The expression which will be used to preview features
+     *                           for this layer
+     *  @note added in 2.0
+     */
+    void setDisplayExpression( const QString displayExpression );
+
+    /**
+     *  Get the preview expression, used to create a human readable preview string.
+     *  Uses @link {QgsExpression}.
+     *
+     *  @return The expression which will be used to preview features for this layer
+     *  @note added in 2.0
+     */
+    const QString displayExpression();
+
     /** Returns the data provider */
     QgsVectorDataProvider* dataProvider();
 
@@ -973,6 +991,9 @@ class CORE_EXPORT QgsVectorLayer : public QgsMapLayer
     /** index of the primary label field */
     QString mDisplayField;
 
+    /** the preview expression used to generate a human readable preview string for features */
+    QString mDisplayExpression;
+
     /** Data provider key */
     QString mProviderKey;
 

src/gui/attributetable/qgsdualview.cpp

@@ -46,6 +46,7 @@ QgsDualView::QgsDualView( QWidget* parent )
   // Connect layer list preview signals
   connect( mActionExpressionPreview, SIGNAL( triggered() ), SLOT( previewExpressionBuilder() ) );
   connect( mPreviewActionMapper, SIGNAL( mapped( QObject* ) ), SLOT( previewColumnChanged( QObject* ) ) );
+  connect( mFeatureList, SIGNAL( displayExpressionChanged(QString) ), this, SLOT( previewExpressionChanged(QString) ) );
 }
 
 QgsDualView::~QgsDualView()
@@ -76,6 +77,54 @@ void QgsDualView::init( QgsVectorLayer* layer, QgsMapCanvas* mapCanvas, QgsDista
 
 void QgsDualView::columnBoxInit()
 {
+  // load fields
+  QList<QgsField> fields = mLayerCache->layer()->pendingFields().toList();
+
+  // default expression: saved value
+  QString displayExpression = mLayerCache->layer()->displayExpression();
+
+  // if no display expression is saved: use display field instead
+  if ( displayExpression == "" )
+  {
+    displayExpression = mLayerCache->layer()->displayField();
+  }
+
+  // if neither diaplay expression nor display field is saved...
+  if ( displayExpression == "" )
+  {
+    QgsAttributeList pkAttrs = mLayerCache->layer()->pendingPkAttributesList();
+
+    if ( pkAttrs.size() > 0 )
+    {
+      // ... If there are primary key(s) defined
+      QStringList pkFields;
+
+      foreach ( int attr, pkAttrs )
+      {
+        pkFields.append( "\"" + fields[attr].name() + "\"" );
+      }
+
+      displayExpression = pkFields.join( "||', '||" );
+    }
+    else if ( fields.size() > 0 )
+    {
+      // ... concat all fields
+      QStringList fieldNames;
+      foreach ( QgsField field, fields )
+      {
+        fieldNames.append( "\"" + field.name() + "\"" );
+      }
+
+      displayExpression = fieldNames.join( "||', '||" );
+    }
+    else
+    {
+      // ... there isn't really much to display
+      displayExpression = "[Please define preview text]";
+    }
+  }
+
+  // now initialise the menu
   QList< QAction* > previewActions = mFeatureListPreviewButton->actions();
   foreach ( QAction* a, previewActions )
   {
@@ -89,8 +138,6 @@ void QgsDualView::columnBoxInit()
   mFeatureListPreviewButton->addAction( mActionExpressionPreview );
   mFeatureListPreviewButton->addAction( mActionPreviewColumnsMenu );
 
-  QList<QgsField> fields = mLayerCache->layer()->pendingFields().toList();
-
   foreach ( const QgsField field, fields )
   {
     if ( mLayerCache->layer()->editType( mLayerCache->layer()->fieldNameIndex( field.name() ) ) != QgsVectorLayer::Hidden )
@@ -104,45 +151,18 @@ void QgsDualView::columnBoxInit()
       connect( previewAction, SIGNAL( triggered() ), mPreviewActionMapper, SLOT( map() ) );
       mPreviewColumnsMenu->addAction( previewAction );
 
-      if ( text == mLayerCache->layer()->displayField() )
+      if ( text == displayExpression )
       {
         mFeatureListPreviewButton->setDefaultAction( previewAction );
       }
     }
   }
 
-  // Most likely no displayField is defined
-  // Join primary key fields
+  // If there is no single field found as preview
   if ( !mFeatureListPreviewButton->defaultAction() )
   {
+    mFeatureList->setDisplayExpression( displayExpression );
     mFeatureListPreviewButton->setDefaultAction( mActionExpressionPreview );
-    QgsAttributeList pkAttrs = mLayerCache->layer()->pendingPkAttributesList();
-    // If there is a primary key defined
-    if ( pkAttrs.size() > 0 )
-    {
-      QStringList pkFields;
-
-      foreach ( int attr, pkAttrs )
-      {
-        pkFields.append( "\"" + fields[attr].name() + "\"" );
-      }
-
-      mFeatureList->setDisplayExpression( pkFields.join( "||', '||" ) );
-    }
-    else if ( fields.size() > 0 )
-    {
-      QStringList fieldNames;
-      foreach ( QgsField field, fields )
-      {
-        fieldNames.append( "\"" + field.name() + "\"" );
-      }
-
-      mFeatureList->setDisplayExpression( fieldNames.join( "||', '||" ) );
-    }
-    else
-    {
-      mFeatureList->setDisplayExpression( "[Please define preview text]" );
-    }
   }
   else
   {
@@ -193,6 +213,7 @@ void QgsDualView::initModels( QgsMapCanvas* mapCanvas )
   mFilterModel = new QgsAttributeTableFilterModel( mapCanvas, mMasterModel, mMasterModel );
 
   connect( mFilterModel, SIGNAL( filterInvalidated() ), this, SIGNAL( filterChanged() ) );
+  connect( mFeatureList, SIGNAL( displayExpressionChanged(QString) ), this, SIGNAL( displayExpressionChanged(QString) ) );
 
   mFeatureListModel = new QgsFeatureListModel( mFilterModel, mFilterModel );
 }
@@ -275,9 +296,11 @@ void QgsDualView::previewColumnChanged( QObject* action )
                             .arg( mFeatureList->parserErrorString() )
                           );
     }
-
-    mFeatureListPreviewButton->setDefaultAction( previewAction );
-    mFeatureListPreviewButton->setPopupMode( QToolButton::InstantPopup );
+    else
+    {
+      mFeatureListPreviewButton->setDefaultAction( previewAction );
+      mFeatureListPreviewButton->setPopupMode( QToolButton::InstantPopup );
+    }
   }
 
   Q_ASSERT( previewAction );
@@ -328,6 +351,11 @@ void QgsDualView::viewWillShowContextMenu( QMenu* menu, QModelIndex atIndex )
   menu->addAction( tr( "Open form" ), a, SLOT( featureForm() ) );
 }
 
+void QgsDualView::previewExpressionChanged( const QString expression )
+{
+  mLayerCache->layer()->setDisplayExpression( expression );
+}
+
 void QgsDualView::setFilteredFeatures( QgsFeatureIds filteredFeatures )
 {
   mFilterModel->setFilteredFeatures( filteredFeatures );

src/gui/attributetable/qgsdualview.h

@@ -98,6 +98,15 @@ class GUI_EXPORT QgsDualView : public QStackedWidget, private Ui::QgsDualViewBas
     void  setCurrentEditSelection( const QgsFeatureIds& fids );
 
   signals:
+    /**
+     * Is emitted, whenever the display expression is successfully changed
+     * @param The expression that was applied
+     */
+    void displayExpressionChanged( const QString expression );
+
+    /**
+     * Is emitted, whenever the filter changes
+     */
     void filterChanged();
 
   private slots:
@@ -114,6 +123,8 @@ class GUI_EXPORT QgsDualView : public QStackedWidget, private Ui::QgsDualViewBas
 
     void viewWillShowContextMenu( QMenu* menu, QModelIndex atIndex );
 
+    void previewExpressionChanged( const QString expression );
+
     /**
      * Will be called periodically, when loading layers from slow data providers.
      *

src/gui/attributetable/qgsfeaturelistview.cpp

@@ -73,7 +73,15 @@ void QgsFeatureListView::setModel( QgsFeatureListModel* featureListModel )
 
 bool QgsFeatureListView::setDisplayExpression( const QString expression )
 {
-  return mModel->setDisplayExpression( expression );
+  if ( mModel->setDisplayExpression( expression ) )
+  {
+    emit displayExpressionChanged( expression );
+    return true;
+  }
+  else
+  {
+    return false;
+  }
 }
 
 const QString& QgsFeatureListView::displayExpression() const

src/gui/attributetable/qgsfeaturelistview.h

@@ -111,6 +111,12 @@ class GUI_EXPORT QgsFeatureListView : public QListView
      */
     void currentEditSelectionChanged( QgsFeature &feat );
 
+    /**
+     * Is emitted, whenever the display expression is successfully changed
+     * @param The expression that was applied
+     */
+    void displayExpressionChanged( const QString expression );
+
   public slots:
     /**
      * Set the feature(s) to be edited