+ use undo/redo for Fem constraint force dialog

src/Mod/Fem/App/FemConstraintForce.cpp

@@ -82,6 +82,10 @@ void ConstraintForce::onChanged(const App::Property* prop)
             direction = -direction;
         DirectionVector.setValue(direction);
     } else if (prop == &Reversed) {
+        // if the direction is invalid try to compute it again
+        if (naturalDirectionVector.Length() < Precision::Confusion()) {
+            naturalDirectionVector = getDirection(Direction);
+        }
         if (naturalDirectionVector.Length() >= Precision::Confusion()) {
             if (Reversed.getValue() && (DirectionVector.getValue() == naturalDirectionVector)) {
                 DirectionVector.setValue(-naturalDirectionVector);

src/Mod/Fem/Gui/TaskFemConstraintForce.cpp

@@ -329,6 +329,15 @@ TaskDlgFemConstraintForce::TaskDlgFemConstraintForce(ViewProviderFemConstraintFo
 
 //==== calls from the TaskView ===============================================================
 
+void TaskDlgFemConstraintForce::open()
+{
+    // a transaction is already open at creation time of the panel
+    if (!Gui::Command::hasPendingCommand()) {
+        QString msg = QObject::tr("Constraint force");
+        Gui::Command::openCommand((const char*)msg.toUtf8());
+    }
+}
+
 bool TaskDlgFemConstraintForce::accept()
 {
     std::string name = ConstraintView->getObject()->getNameInDocument();
@@ -360,4 +369,14 @@ bool TaskDlgFemConstraintForce::accept()
     return TaskDlgFemConstraint::accept();
 }
 
+bool TaskDlgFemConstraintForce::reject()
+{
+    // roll back the changes
+    Gui::Command::abortCommand();
+    Gui::Command::doCommand(Gui::Command::Gui,"Gui.activeDocument().resetEdit()");
+    Gui::Command::updateActive();
+
+    return true;
+}
+
 #include "moc_TaskFemConstraintForce.cpp"

src/Mod/Fem/Gui/TaskFemConstraintForce.h

@@ -83,7 +83,9 @@ public:
     TaskDlgFemConstraintForce(ViewProviderFemConstraintForce *ConstraintView);
 
     /// is called by the framework if the dialog is accepted (Ok)
+    virtual void open();
     virtual bool accept();
+    virtual bool reject();
 
 };