+
+ redef fun on_save_state
+ do
+ app.data_store["context"] = context
+ super
+ end
+
+ redef fun on_restore_state
+ do
+ super
+
+ var context = app.data_store["context"]
+ if not context isa CalculatorContext then return
+
+ self.context = context
+ display.text = context.display_text
+ end