quick_frontend (app, widget): CagouWidget.onSelected is called when the widget is selected:

A property is now used to manage `selected_widget` in QuickApp, and widget's onSelected
method is called when suitable.

sat_frontends/quick_frontend/quick_app.py

@@ -301,8 +301,8 @@ class QuickApp(object):
         else:
             self.options = None
 
-        # widget currently selected (must be filled by frontend)
-        self.selected_widget = None
+        # see selected_widget setter and getter
+        self._selected_widget = None
 
         # listeners are callable watching events
         self._listeners = {}  # key: listener type ("avatar", "selected", etc),
@@ -436,6 +436,28 @@ class QuickApp(object):
             if isinstance(w, quick_widgets.QuickWidget):
                 return w
 
+    @property
+    def selected_widget(self):
+        """widget currently selected
+
+        This must be set by frontend using setter.
+        """
+        return self._selected_widget
+
+    @selected_widget.setter
+    def selected_widget(self, wid):
+        """Set the currently selected widget
+
+        Must be set by frontend
+        """
+        self._selected_widget = wid
+        try:
+            onSelected = wid.onSelected
+        except AttributeError:
+            pass
+        else:
+            onSelected()
+
     # backend state management
 
     @property