FieldExpressionWidget: preserve expression when join is removed

Author: m-kuhn

src/gui/qgsfieldexpressionwidget.cpp

@@ -58,6 +58,8 @@ QgsFieldExpressionWidget::QgsFieldExpressionWidget( QWidget *parent )
   connect( mCombo->lineEdit(), SIGNAL( editingFinished() ), this, SLOT( expressionEditingFinished() ) );
   connect( mCombo, SIGNAL( activated( int ) ), this, SLOT( currentFieldChanged() ) );
   connect( mButton, SIGNAL( clicked() ), this, SLOT( editExpression() ) );
+  connect( mFieldProxyModel, SIGNAL( modelAboutToBeReset() ), this, SLOT( beforeResetModel() ) );
+  connect( mFieldProxyModel, SIGNAL( modelReset() ), this, SLOT( afterResetModel() ) );
   // NW TODO - Fix in 2.6
 //  connect( mCombo->lineEdit(), SIGNAL( returnPressed() ), this, SIGNAL( returnPressed() ) );
 
@@ -158,7 +160,7 @@ void QgsFieldExpressionWidget::setLayer( QgsVectorLayer *layer )
 
   mFieldProxyModel->sourceFieldModel()->setLayer( layer );
 
-  connect( mFieldProxyModel->sourceFieldModel()->layer(), SIGNAL( updatedFields() ), this, SLOT( reloadLayer() ) );
+  connect( mFieldProxyModel->sourceFieldModel()->layer(), SIGNAL( updatedFields() ), SLOT( reloadLayer() ), Qt::UniqueConnection );
 }
 
 void QgsFieldExpressionWidget::setField( const QString &fieldName )
@@ -240,6 +242,18 @@ void QgsFieldExpressionWidget::reloadLayer()
   setLayer( mFieldProxyModel->sourceFieldModel()->layer() );
 }
 
+void QgsFieldExpressionWidget::beforeResetModel()
+{
+  // Backup expression
+  mBackupExpression = mCombo->currentText();
+}
+
+void QgsFieldExpressionWidget::afterResetModel()
+{
+  // Restore expression
+  mCombo->lineEdit()->setText( mBackupExpression );
+}
+
 void QgsFieldExpressionWidget::currentFieldChanged()
 {
   updateLineEditStyle();

src/gui/qgsfieldexpressionwidget.h

@@ -150,6 +150,9 @@ class GUI_EXPORT QgsFieldExpressionWidget : public QWidget
   private slots:
     void reloadLayer();
 
+    void beforeResetModel();
+    void afterResetModel();
+
   private:
     QComboBox* mCombo;
     QToolButton* mButton;
@@ -159,6 +162,7 @@ class GUI_EXPORT QgsFieldExpressionWidget : public QWidget
     QScopedPointer< QgsExpressionContext > mExpressionContext;
     ExpressionContextCallback mExpressionContextCallback;
     const void* mExpressionContextCallbackContext;
+    QString mBackupExpression;
 
     friend class TestQgsFieldExpressionWidget;
 };

src/gui/qgsfieldmodel.h

@@ -67,6 +67,13 @@ class GUI_EXPORT QgsFieldModel : public QAbstractItemModel
     //! returns the currently used layer
     QgsVectorLayer* layer() { return mLayer; }
 
+    // QAbstractItemModel interface
+    QModelIndex index( int row, int column, const QModelIndex &parent = QModelIndex() ) const override;
+    QModelIndex parent( const QModelIndex &child ) const override;
+    int rowCount( const QModelIndex &parent = QModelIndex() ) const override;
+    int columnCount( const QModelIndex &parent ) const override;
+    QVariant data( const QModelIndex &index, int role ) const override;
+
   public slots:
     //! set the layer of whch fields are displayed
     void setLayer( QgsVectorLayer *layer );
@@ -86,14 +93,6 @@ class GUI_EXPORT QgsFieldModel : public QAbstractItemModel
 
   private:
     void fetchFeature();
-
-    // QAbstractItemModel interface
-  public:
-    QModelIndex index( int row, int column, const QModelIndex &parent = QModelIndex() ) const override;
-    QModelIndex parent( const QModelIndex &child ) const override;
-    int rowCount( const QModelIndex &parent = QModelIndex() ) const override;
-    int columnCount( const QModelIndex &parent ) const override;
-    QVariant data( const QModelIndex &index, int role ) const override;
 };
 
 #endif // QGSFIELDMODEL_H