fix crash deleting expression field when layer is not editable

Author: brushtyler

src/core/qgsvectorlayer.cpp

@@ -2954,6 +2954,7 @@ const QList< QgsVectorJoinInfo > QgsVectorLayer::vectorJoins() const
 
 int QgsVectorLayer::addExpressionField( const QString& exp, const QgsField& fld )
 {
+  emit beforeAddingExpressionField( fld.name() );
   mExpressionFieldBuffer->addExpression( exp, fld );
   updateFields();
   int idx = mUpdatedFields.indexFromName( fld.name() );
@@ -2963,6 +2964,7 @@ int QgsVectorLayer::addExpressionField( const QString& exp, const QgsField& fld
 
 void QgsVectorLayer::removeExpressionField( int index )
 {
+  emit beforeRemovingExpressionField( index );
   int oi = mUpdatedFields.fieldOriginIndex( index );
   mExpressionFieldBuffer->removeExpression( oi );
   updateFields();

src/core/qgsvectorlayer.h

@@ -1874,22 +1874,37 @@ class CORE_EXPORT QgsVectorLayer : public QgsMapLayer
 
     /**
      * Will be emitted, when a new attribute has been added to this vector layer.
-     * Applies only to types {@link QgsFields::OriginEdit} and {@link QgsFields::OriginProvider}
+     * Applies only to types {@link QgsFields::OriginEdit}, {@link QgsFields::OriginProvider} and {@link QgsFields::OriginExpression }
      *
      * @param idx The index of the new attribute
      *
      * @see updatedFields()
      */
     void attributeAdded( int idx );
+    /**
+     * Will be emitted, when an expression field is going to be added to this vector layer.
+     * Applies only to types {@link QgsFields::OriginExpression }
+     *
+     * @param fieldName The name of the attribute to be added
+     */
+    void beforeAddingExpressionField( QString fieldName );
     /**
      * Will be emitted, when an attribute has been deleted from this vector layer.
-     * Applies only to types {@link QgsFields::OriginEdit} and {@link QgsFields::OriginProvider}
+     * Applies only to types {@link QgsFields::OriginEdit}, {@link QgsFields::OriginProvider} and {@link QgsFields::OriginExpression }
      *
      * @param idx The index of the deleted attribute
      *
      * @see updatedFields()
      */
     void attributeDeleted( int idx );
+    /**
+     * Will be emitted, when an expression field is going to be deleted from this vector layer.
+     * Applies only to types {@link QgsFields::OriginExpression }
+     *
+     * @param idx The index of the attribute to be deleted
+     */
+    void beforeRemovingExpressionField( int idx );
+
     /**
      * Emitted when a new feature has been added to the layer
      *

src/gui/qgsattributeform.cpp

@@ -45,6 +45,7 @@ QgsAttributeForm::QgsAttributeForm( QgsVectorLayer* vl, const QgsFeature &featur
     , mFormNr( sFormCounter++ )
     , mIsSaving( false )
     , mIsAddDialog( false )
+    , mPreventFeatureRefresh( false )
     , mEditCommandMessage( tr( "Attributes changed" ) )
 {
   init();
@@ -53,6 +54,8 @@ QgsAttributeForm::QgsAttributeForm( QgsVectorLayer* vl, const QgsFeature &featur
 
   connect( vl, SIGNAL( attributeAdded( int ) ), this, SLOT( onAttributeAdded( int ) ) );
   connect( vl, SIGNAL( attributeDeleted( int ) ), this, SLOT( onAttributeDeleted( int ) ) );
+  connect( vl, SIGNAL( beforeAddingExpressionField( QString ) ), this, SLOT( preventFeatureRefresh() ) );
+  connect( vl, SIGNAL( beforeRemovingExpressionField( int ) ), this, SLOT( preventFeatureRefresh() ) );
 }
 
 QgsAttributeForm::~QgsAttributeForm()
@@ -274,7 +277,7 @@ void QgsAttributeForm::onAttributeChanged( const QVariant& value )
 
 void QgsAttributeForm::onAttributeAdded( int idx )
 {
-  Q_UNUSED( idx ) // only used for Q_ASSERT
+  mPreventFeatureRefresh = false;
   if ( mFeature.isValid() )
   {
     QgsAttributes attrs = mFeature.attributes();
@@ -288,6 +291,7 @@ void QgsAttributeForm::onAttributeAdded( int idx )
 
 void QgsAttributeForm::onAttributeDeleted( int idx )
 {
+  mPreventFeatureRefresh = false;
   if ( mFeature.isValid() )
   {
     QgsAttributes attrs = mFeature.attributes();
@@ -299,9 +303,14 @@ void QgsAttributeForm::onAttributeDeleted( int idx )
   setFeature( mFeature );
 }
 
+void QgsAttributeForm::preventFeatureRefresh()
+{
+  mPreventFeatureRefresh = true;
+}
+
 void QgsAttributeForm::refreshFeature()
 {
-  if ( mLayer->isEditable() || !mFeature.isValid() )
+  if ( mPreventFeatureRefresh || mLayer->isEditable() || !mFeature.isValid() )
     return;
 
   // reload feature if layer changed although not editable

src/gui/qgsattributeform.h

@@ -174,6 +174,7 @@ class GUI_EXPORT QgsAttributeForm : public QWidget
     void onAttributeAdded( int idx );
     void onAttributeDeleted( int idx );
 
+    void preventFeatureRefresh();
     void synchronizeEnabledState();
 
   private:
@@ -210,6 +211,9 @@ class GUI_EXPORT QgsAttributeForm : public QWidget
     bool mIsSaving;
     bool mIsAddDialog;
 
+    //! Flag to prevent refreshFeature() to change mFeature
+    bool mPreventFeatureRefresh;
+
     QString mEditCommandMessage;
 };