Account balance title refactoring

Binds/unbinds balance update on screen enter/leave, fixes #80

src/main.py

@@ -390,18 +390,13 @@ def setup(self):
         # triggers the update
         self.current_account = self.controller.current_account
 
-    def is_selected(self):
+    def on_current_account(self, instance, account):
         """
-        Returns True if the overview sub-screen is selected,
-        otherwise returns False.
+        Updates current_account_string and fetches the new account balance.
         """
-        return self.parent.manager.current == 'overview'
-
-    def on_current_account(self, instance, account):
         address = "0x" + account.address.encode("hex")
         self.current_account_string = address
-        if self.is_selected():
-            self.controller.fetch_and_update_balance()
+        self.controller.fetch_balance()
 
 
 class PWSelectList(BoxLayout):
@@ -916,6 +911,18 @@ def screen_manager(self):
     def set_toolbar_title(self, title):
         self.toolbar.title_property = title
 
+    def bind_current_account_balance(self):
+        """
+        Binds the current_account_balance to the Toolbar title.
+        """
+        self.bind(current_account_balance=self.update_toolbar_title_balance)
+
+    def unbind_current_account_balance(self):
+        """
+        Unbinds the current_account_balance from the Toolbar title.
+        """
+        self.unbind(current_account_balance=self.update_toolbar_title_balance)
+
     def screen_manager_current(self, current, direction=None):
         screens = {
             'overview': OverviewScreen,
@@ -1047,7 +1054,7 @@ def show_not_implemented_dialog():
         dialog.open()
 
     @mainthread
-    def update_toolbar_title_balance(self):
+    def update_toolbar_title_balance(self, instance=None, value=None):
         title = "%s ETH" % (self.current_account_balance)
         self.set_toolbar_title(title)
 
@@ -1067,21 +1074,17 @@ def load_landing_page(self):
         except IndexError:
             self.load_create_new_account()
 
-    @run_in_thread
-    def fetch_and_update_balance(self):
+    def fetch_balance(self):
         """
-        Fetches the new balance and updates the UI.
+        Fetches the new balance and current_account_balance property.
         """
-        # pre-updates balance with last known value
-        self.update_toolbar_title_balance()
         account = self.current_account
         try:
             self.current_account_balance = self.pywalib.get_balance(
                 account.address.encode("hex"))
         except ConnectionError:
             Controller.on_balance_connection_error()
             return
-        self.update_toolbar_title_balance()
 
     def load_switch_account(self):
         """

src/pywallet.kv

@@ -321,10 +321,14 @@
         text: "Overview"
         icon: 'format-list-bulleted'
         on_pre_enter:
-            root.parent.set_title("0 ETH")
-            # TODO: not necessarily, e.g. probably not if the account didn't change
-            # TODO: but update title
-            app.controller.fetch_and_update_balance()
+            # sets to the last known value
+            app.controller.update_toolbar_title_balance()
+            # and binds on update
+            app.controller.bind_current_account_balance()
+        on_pre_leave:
+            # makes ure the title doesn't get updated async
+            # if we're not in this screen
+            app.controller.unbind_current_account_balance()
         Overview:
             id: overview_id
     MDBottomNavigationItem:
@@ -358,6 +362,9 @@
         # restores title,
         # e.g. when coming back from the account selection screen
         app.controller.set_toolbar_title(root.title_property)
+        overview_bnavigation_id.ids.tab_manager.current_screen.dispatch('on_pre_enter')
+    on_pre_leave:
+        overview_bnavigation_id.ids.tab_manager.current_screen.dispatch('on_pre_leave')
     on_title_property:
         app.controller.set_toolbar_title(root.title_property)
     OverviewBottomNavigation: