[bugfix] Do not crash when layer is destroyed while loading

Fixes #17636 QGIS crashes when a layer is removed
while loading the attribute table

python/gui/attributetable/qgsdualview.sip

@@ -208,6 +208,12 @@ class QgsDualView : QStackedWidget
 %Docstring
  Copy the content of the selected cell in the clipboard.
 .. versionadded:: 1.16
+%End
+
+    void cancelProgress( );
+%Docstring
+ Cancel the progress dialog (if any)
+.. versionadded:: 3.0
 %End
 
   signals:

src/app/qgsattributetabledialog.cpp

@@ -69,7 +69,7 @@ QgsExpressionContext QgsAttributeTableDialog::createExpressionContext() const
 
 void QgsAttributeTableDialog::updateMultiEditButtonState()
 {
-  if ( mLayer->editFormConfig().layout() == QgsEditFormConfig::UiFileLayout )
+  if ( ! mLayer || ( mLayer->editFormConfig().layout() == QgsEditFormConfig::UiFileLayout ) )
     return;
 
   mActionToggleMultiEdit->setEnabled( mLayer->isEditable() );
@@ -199,7 +199,7 @@ QgsAttributeTableDialog::QgsAttributeTableDialog( QgsVectorLayer *layer, QgsAttr
   // info from layer to table
   connect( mLayer, &QgsVectorLayer::editingStarted, this, &QgsAttributeTableDialog::editingToggled );
   connect( mLayer, &QgsVectorLayer::editingStopped, this, &QgsAttributeTableDialog::editingToggled );
-  connect( mLayer, &QObject::destroyed, this, &QWidget::close );
+  connect( mLayer, &QObject::destroyed, mMainView, &QgsDualView::cancelProgress );
   connect( mLayer, &QgsVectorLayer::selectionChanged, this, &QgsAttributeTableDialog::updateTitle );
   connect( mLayer, &QgsVectorLayer::featureAdded, this, &QgsAttributeTableDialog::updateTitle );
   connect( mLayer, &QgsVectorLayer::featuresDeleted, this, &QgsAttributeTableDialog::updateTitle );
@@ -292,6 +292,9 @@ QgsAttributeTableDialog::QgsAttributeTableDialog( QgsVectorLayer *layer, QgsAttr
       break;
   }
 
+  // Layer might have been destroyed while loading!
+  if ( mLayer )
+  {
     mUpdateExpressionText->registerExpressionContextGenerator( this );
     mFieldCombo->setFilters( QgsFieldProxyModel::AllTypes | QgsFieldProxyModel::HideReadOnly );
     mFieldCombo->setLayer( mLayer );
@@ -345,6 +348,13 @@ QgsAttributeTableDialog::QgsAttributeTableDialog( QgsVectorLayer *layer, QgsAttr
     }
 
     editingToggled();
+    // Close and delete if the layer has been destroyed
+    connect( mLayer, &QObject::destroyed, this, &QWidget::close );
+  }
+  else
+  {
+    QWidget::close();
+  }
 }
 
 QgsAttributeTableDialog::~QgsAttributeTableDialog()
@@ -354,6 +364,10 @@ QgsAttributeTableDialog::~QgsAttributeTableDialog()
 
 void QgsAttributeTableDialog::updateTitle()
 {
+  if ( ! mLayer )
+  {
+    return;
+  }
   QWidget *w = mDock ? qobject_cast<QWidget *>( mDock ) : qobject_cast<QWidget *>( this );
   w->setWindowTitle( tr( " %1 :: Features Total: %2, Filtered: %3, Selected: %4" )
                      .arg( mLayer->name() )

src/app/qgsattributetabledialog.h

@@ -230,7 +230,7 @@ class APP_EXPORT QgsAttributeTableDialog : public QDialog, private Ui::QgsAttrib
     QMenu *mFilterColumnsMenu = nullptr;
     QSignalMapper *mFilterActionMapper = nullptr;
 
-    QgsVectorLayer *mLayer = nullptr;
+    QPointer< QgsVectorLayer > mLayer = nullptr;
     QgsSearchWidgetWrapper *mCurrentSearchWidgetWrapper = nullptr;
     QStringList mVisibleFields;
     QgsAttributeEditorContext mEditorContext;

src/gui/attributetable/qgsdualview.cpp

@@ -318,6 +318,10 @@ void QgsDualView::restoreRecentDisplayExpressions()
 
 void QgsDualView::saveRecentDisplayExpressions() const
 {
+  if ( ! mLayer )
+  {
+    return;
+  }
   QList<QAction *> actions = mFeatureListPreviewButton->actions();
 
   // Remove existing same action
@@ -397,6 +401,7 @@ void QgsDualView::insertRecentlyUsedDisplayExpression( const QString &expression
   mLastDisplayExpressionAction = previewAction;
 }
 
+
 void QgsDualView::mFeatureList_aboutToChangeEditSelection( bool &ok )
 {
   if ( mLayer->isEditable() && !mAttributeForm->save() )
@@ -515,6 +520,12 @@ void QgsDualView::copyCellContent() const
   }
 }
 
+void QgsDualView::cancelProgress()
+{
+  if ( mProgressDlg )
+    mProgressDlg->cancel();
+}
+
 void QgsDualView::hideEvent( QHideEvent *event )
 {
   Q_UNUSED( event )

src/gui/attributetable/qgsdualview.h

@@ -236,6 +236,12 @@ class GUI_EXPORT QgsDualView : public QStackedWidget, private Ui::QgsDualViewBas
      */
     void copyCellContent() const;
 
+    /**
+     * Cancel the progress dialog (if any)
+     * \since QGIS 3.0
+     */
+    void cancelProgress( );
+
   signals:
 
     /**
@@ -360,7 +366,7 @@ class GUI_EXPORT QgsDualView : public QStackedWidget, private Ui::QgsDualViewBas
     QAction *mLastDisplayExpressionAction = nullptr;
     QMenu *mHorizontalHeaderMenu = nullptr;
     QgsVectorLayerCache *mLayerCache = nullptr;
-    QgsVectorLayer *mLayer = nullptr;
+    QPointer< QgsVectorLayer > mLayer = nullptr;
     QProgressDialog *mProgressDlg = nullptr;
     QgsIFeatureSelectionManager *mFeatureSelectionManager = nullptr;
     QgsDistanceArea mDistanceArea;