view: add way to redraw screen if the view is visible

Views can now redraw themselves using the request_redraw_if_visible()
method. Behind the scenes, it will look if the view is the currently
visible view and skip the redraw otherwise.

Signed-off-by: Olivier Gayot <olivier.gayot@canonical.com>

subiquitycore/view.py

@@ -19,6 +19,7 @@ Contains some default key navigations
 """
 
 import asyncio
+import contextlib
 import logging
 
 from urwid import Overlay, Text, emit_signal
@@ -152,3 +153,16 @@ class BaseView(WidgetWrap):
                 self.cancel()
                 return None
         return key
+
+    def is_visible(self) -> bool:
+        with contextlib.suppress(AttributeError):
+            return self.controller.app.ui.body is self
+        return False
+
+    def request_redraw(self, *, only_if_visible=False) -> None:
+        if only_if_visible and not self.is_visible():
+            return
+        self.controller.app.request_screen_redraw()
+
+    def request_redraw_if_visible(self) -> None:
+        self.request_redraw(only_if_visible=True)