Gui: [skip ci] allow to unbind() an ExpressionBinding and automatically unbind it if the observed object has been deleted

For more details see: https://forum.freecadweb.org/viewtopic.php?f=8&t=56097

src/Gui/ExpressionBinding.cpp

@@ -59,6 +59,13 @@ bool ExpressionBinding::isBound() const
     return path.getDocumentObject() != 0;
 }
 
+void ExpressionBinding::unbind()
+{
+    expressionchanged.disconnect();
+    objectdeleted.disconnect();
+    path = App::ObjectIdentifier();
+}
+
 void Gui::ExpressionBinding::setExpression(boost::shared_ptr<Expression> expr)
 {
     DocumentObject * docObj = path.getDocumentObject();
@@ -100,7 +107,11 @@ void ExpressionBinding::bind(const App::ObjectIdentifier &_path)
 
     //connect to be informed about changes
     DocumentObject * docObj = path.getDocumentObject();
-    connection = docObj->ExpressionEngine.expressionChanged.connect(boost::bind(&ExpressionBinding::expressionChange, this, bp::_1));
+    if (docObj) {
+        expressionchanged = docObj->ExpressionEngine.expressionChanged.connect(boost::bind(&ExpressionBinding::expressionChange, this, bp::_1));
+        App::Document* doc = docObj->getDocument();
+        objectdeleted = doc->signalDeletedObject.connect(boost::bind(&ExpressionBinding::objectDeleted, this, bp::_1));
+    }
 }
 
 void ExpressionBinding::bind(const Property &prop)
@@ -247,3 +258,11 @@ void ExpressionBinding::expressionChange(const ObjectIdentifier& id) {
     if(id==path)
         onChange();
 }
+
+void ExpressionBinding::objectDeleted(const App::DocumentObject& obj)
+{
+    DocumentObject * docObj = path.getDocumentObject();
+    if (docObj == &obj) {
+        unbind();
+    }
+}

src/Gui/ExpressionBinding.h

@@ -44,6 +44,7 @@ public:
     virtual void bind(const App::ObjectIdentifier & _path);
     virtual void bind(const App::Property & prop);
     bool isBound() const;
+    void unbind();
     virtual bool apply(const std::string &propName);
     virtual bool apply();
     bool hasExpression() const;
@@ -52,8 +53,8 @@ public:
 
     //auto apply means that the python code is issued not only on apply() but
     //also on setExpression
-    bool autoApply() const {return m_autoApply;};
-    void setAutoApply(bool value) {m_autoApply = value;};
+    bool autoApply() const {return m_autoApply;}
+    void setAutoApply(bool value) {m_autoApply = value;}
 
 protected:
     const App::ObjectIdentifier & getPath() const { return path; }
@@ -63,7 +64,7 @@ protected:
     virtual void setExpression(boost::shared_ptr<App::Expression> expr);
 
     //gets called when the bound expression is changed, either by this binding or any external action
-    virtual void onChange() {};
+    virtual void onChange() {}
 
 private:
     App::ObjectIdentifier path;
@@ -75,7 +76,9 @@ protected:
     int iconHeight;
 
     void expressionChange(const App::ObjectIdentifier& id);
-    boost::signals2::scoped_connection connection;
+    void objectDeleted(const App::DocumentObject&);
+    boost::signals2::scoped_connection expressionchanged;
+    boost::signals2::scoped_connection objectdeleted;
     bool m_autoApply;
 };