Gui: Add getObject<T>() helpers to various classes

Obtaining specific kind of document object is very common task. This
commit introduces handy helper which makes that a lot easier.

src/Gui/SelectionObject.h

@@ -71,9 +71,15 @@ public:
     inline const std::vector<Base::Vector3d> getPickedPoints() const { return SelPoses; }
 
     /// returns the selected DocumentObject or NULL if the object is already deleted
-    const App::DocumentObject *getObject() const;
+    const App::DocumentObject* getObject() const;
+    /// returns the selected DocumentObject or NULL if the object is already deleted
+    template <class T>
+    const T* getObject() const { return dynamic_cast<T*>(getObject()); };
     /// returns the selected DocumentObject or NULL if the object is already deleted
     App::DocumentObject *getObject();
+    /// returns the selected DocumentObject if it is of T type or null otherwise
+    template <class T>
+    T* getObject() { return dynamic_cast<T*>(getObject()); }
 
     /// check the selected object is a special type or derived of
     bool isObjectTypeOf(const Base::Type& typeId) const;

src/Gui/ViewProviderDocumentObject.h

@@ -92,6 +92,9 @@ public:
     void updateView();
     /// Get the object of this ViewProvider object
     App::DocumentObject *getObject() const {return pcObject;}
+    /// Get the object of this ViewProvider object as specified type
+    template <class T>
+    T *getObject() const { return dynamic_cast<T*>(pcObject); }
     /// Asks the view provider if the given object can be deleted.
     bool canDelete(App::DocumentObject* obj) const override;
     /// Ask the view provider if it accepts object deletions while in edit

src/Gui/ViewProviderGeometryObject.cpp

@@ -173,7 +173,7 @@ void ViewProviderGeometryObject::updateData(const App::Property* prop)
         pcBoundingBox->maxBounds.setValue(box.MaxX, box.MaxY, box.MaxZ);
     }
     else if (prop->isDerivedFrom(App::PropertyPlacement::getClassTypeId())) {
-        auto geometry = dynamic_cast<App::GeoFeature*>(getObject());
+        auto geometry = getObject<App::GeoFeature>();
         if (geometry && prop == &geometry->Placement) {
             const App::PropertyComplexGeoData* data = geometry->getPropertyOfGeometry();
             if (data) {
@@ -185,8 +185,7 @@ void ViewProviderGeometryObject::updateData(const App::Property* prop)
     }
     else if (std::string(prop->getName()) == "ShapeMaterial") {
         // Set the appearance from the material
-        auto geometry = dynamic_cast<App::GeoFeature*>(getObject());
-        if (geometry) {
+        if (auto geometry = getObject<App::GeoFeature>()) {
             /*
              * Change the appearance only if the appearance hasn't been set explicitly. A cached
              * material appearance is used to see if the current appearance matches the last

src/Mod/Fem/Gui/ViewProviderFemPostFunction.h

@@ -65,10 +65,15 @@ protected:
     {
         return m_view;
     }
-    Fem::FemPostFunction* getObject()
+    Fem::FemPostFunction* getObject() const
     {
         return m_object;
     }
+    template<class T>
+    T* getObject() const
+    {
+        return dynamic_cast<T*>(getObject());
+    }
 
     bool blockObjectUpdates()
     {

src/Mod/PartDesign/Gui/TaskTransformedParameters.h

@@ -178,6 +178,9 @@ protected:
      */
     PartDesign::Transformed* getObject() const;
 
+    template <class T>
+    T* getObject() const { return dynamic_cast<T*>(getObject()); }
+
     /// Get the sketch object of the first original either of the object associated with this
     /// feature or with the parent feature (MultiTransform mode)
     App::DocumentObject* getSketchObject() const;

src/Mod/TechDraw/App/DimensionReferences.h

@@ -63,6 +63,7 @@ public:
     bool operator== (const ReferenceEntry& otherRef) const;
 
     App::DocumentObject* getObject() const;
+    template <class T> T* getObject() const { return dynamic_cast<T*>(getObject()); }
     void setObject(App::DocumentObject* docObj) { m_object = docObj; }
     std::string getSubName(bool longForm = false) const;
     void setSubName(const std::string& subName) { m_subName = subName; }