Context as Activity member; on_destroy context is released

src/ui/activities/mod.rs

@@ -38,17 +38,19 @@ pub trait Activity {
     ///
     /// `on_create` is the function which must be called to initialize the activity.
     /// `on_create` must initialize all the data structures used by the activity
-    fn on_create(&mut self, context: &mut Context);
+    /// Context is taken from activity manager and will be released only when activity is destroyed
+    fn on_create(&mut self, context: Context);
 
     /// ### on_draw
     ///
     /// `on_draw` is the function which draws the graphical interface.
     /// This function must be called at each tick to refresh the interface
-    fn on_draw(&mut self, context: &mut Context);
+    fn on_draw(&mut self);
 
     /// ### on_destroy
     ///
     /// `on_destroy` is the function which cleans up runtime variables and data before terminating the activity.
     /// This function must be called once before terminating the activity.
-    fn on_destroy(&mut self, context: &mut Context);
+    /// This function finally releases the context
+    fn on_destroy(&mut self) -> Option<Context>;
 }