fix crash when cancelling revolution task panel

src/Mod/PartDesign/Gui/TaskFeatureParameters.cpp

@@ -45,7 +45,17 @@ TaskFeatureParameters::TaskFeatureParameters(PartDesignGui::ViewProvider *vp, QW
                                                      const std::string& pixmapname, const QString& parname)
     : TaskBox(Gui::BitmapFactory().pixmap(pixmapname.c_str()),parname,true, parent),
       vp(vp), blockUpdate(false)
-{ }
+{
+    Gui::Document* doc = vp->getDocument();
+    this->attachDocument(doc);
+    this->enableNotifications(DocumentObserver::Delete);
+}
+
+void TaskFeatureParameters::slotDeletedObject(const Gui::ViewProviderDocumentObject& Obj)
+{
+    if (this->vp == &Obj)
+        this->vp = nullptr;
+}
 
 void TaskFeatureParameters::onUpdateView(bool on)
 {

src/Mod/PartDesign/Gui/TaskFeatureParameters.h

@@ -26,25 +26,27 @@
 
 #include <Gui/TaskView/TaskView.h>
 #include <Gui/TaskView/TaskDialog.h>
+#include <Gui/DocumentObserver.h>
 
 #include "ViewProvider.h"
 
 namespace PartDesignGui {
 
 /// Convenience class to collect common methods for all SketchBased features
-class TaskFeatureParameters : public Gui::TaskView::TaskBox
+class TaskFeatureParameters : public Gui::TaskView::TaskBox,
+                              public Gui::DocumentObserver
 {
     Q_OBJECT
 
 public:
     TaskFeatureParameters(PartDesignGui::ViewProvider* vp, QWidget *parent,
                               const std::string& pixmapname, const QString& parname);
-    virtual ~TaskFeatureParameters() {};
+    virtual ~TaskFeatureParameters() {}
 
     /// save field history
-    virtual void saveHistory(void) {};
+    virtual void saveHistory(void) {}
     /// apply changes made in the parameters input to the model via commands
-    virtual void apply() {};
+    virtual void apply() {}
 
     void recomputeFeature();
 
@@ -52,6 +54,10 @@ protected Q_SLOTS:
     // TODO Add update view to all dialogs (2015-12-05, Fat-Zer)
     void onUpdateView(bool on);
 
+private:
+    /** Notifies when the object is about to be removed. */
+    virtual void slotDeletedObject(const Gui::ViewProviderDocumentObject& Obj);
+
 protected:
     PartDesignGui::ViewProvider *vp;
     /// Lock updateUI(), applying changes to the underlying feature and calling recomputeFeature()

src/Mod/PartDesign/Gui/TaskRevolutionParameters.cpp

@@ -361,8 +361,8 @@ bool   TaskRevolutionParameters::getReversed(void) const
 TaskRevolutionParameters::~TaskRevolutionParameters()
 {
     //hide the parts coordinate system axis for selection
-    PartDesign::Body * body = PartDesign::Body::findBodyOf ( vp->getObject() );
-    if ( body ) {
+    PartDesign::Body * body = vp ? PartDesign::Body::findBodyOf(vp->getObject()) : 0;
+    if (body) {
         try {
             App::Origin *origin = body->getOrigin();
             ViewProviderOrigin* vpOrigin;
@@ -375,7 +375,7 @@ TaskRevolutionParameters::~TaskRevolutionParameters()
 
     delete ui;
 
-    for(size_t i = 0  ;  i < axesInList.size()  ;  i++ ){
+    for (size_t i = 0; i < axesInList.size(); i++) {
         delete axesInList[i];
     }
 }