D-Bus error management

src/sensors_polling_timer.py

@@ -1,5 +1,6 @@
 from gi.repository import Gio, GLib
 from threading import Timer
+from enum import Enum
 
 # window.py
 #
@@ -20,7 +21,6 @@ from threading import Timer
 #
 # SPDX-License-Identifier: GPL-3.0-or-later
 
-
 # A timer for polling the light sensor via DBus.
 # Checks the sensor at a specific interval and runs a callback only when an update is detected.
 #
@@ -28,17 +28,30 @@ from threading import Timer
 # Instantiate it, then call run(interval_in_seconds, callback_function)
 # To stop it, call cancel()
 class SensorsPollingTimer(Timer):
+
     def run(self):
         # Setup
-        bus = Gio.bus_get_sync(Gio.BusType.SYSTEM, None)
-        self.proxy = Gio.DBusProxy.new_sync(bus,Gio.DBusProxyFlags.NONE,None,'net.hadess.SensorProxy','/net/hadess/SensorProxy','org.freedesktop.DBus.Properties', None)
-        self.oldValue = None
+        try:
+            bus = Gio.bus_get_sync(Gio.BusType.SYSTEM, None)
+            self.proxy = Gio.DBusProxy.new_sync(bus,Gio.DBusProxyFlags.NONE,None,'net.hadess.SensorProxy','/net/hadess/SensorProxy','org.freedesktop.DBus.Properties', None)
 
-        # Loop
-        while not self.finished.wait(self.interval):
-            value = self.proxy.Get('(ss)', 'net.hadess.SensorProxy', 'LightLevel')
-            if (self.oldValue != value):
-                self.oldValue = value
-                unit = self.proxy.Get('(ss)', 'net.hadess.SensorProxy', 'LightLevelUnit')
-                self.function(value, unit)    # Invoke callback
+            self.oldValue = None
+
+            # Loop
+            while not self.finished.wait(self.interval):
+                value = self.proxy.Get('(ss)', 'net.hadess.SensorProxy', 'LightLevel')
+                if (self.oldValue != value):
+                    self.oldValue = value
+                    unit = self.proxy.Get('(ss)', 'net.hadess.SensorProxy', 'LightLevelUnit')
+                    self.function(value, unit)    # Invoke callback
+
+        except Exception as e:
+            if not self.onError:
+                print("SensorsPollingTimer: error occurred, but no onError callback defined")
+                return
+
+            self.onError(e)
+
+    def setOnErrorListener(onError):
+        self.onError = onError
 

src/window.py

@@ -25,17 +25,22 @@ from .ev_calculator import EVCalculator
 class LumosWindow(Adw.ApplicationWindow):
     __gtype_name__ = 'LumosWindow'
 
+    # Labels
     lux_label = Gtk.Template.Child()
     ev_label = Gtk.Template.Child()
+    error_banner = Gtk.Template.Child()
 
     def __init__(self, **kwargs):
         super().__init__(**kwargs)
 
+        self.lastError = None
+
         # Register for window lifecycle events
         self.connect("close-request", self.__on_close_request)
 
         # Start polling sensors
         self.sensorsPollingTimer = SensorsPollingTimer(0.1, self.onSensorRead)
+        self.sensorsPollingTimer.onError = self.onError
         self.sensorsPollingTimer.start()
 
     def __on_close_request(self, _obj: GObject.Object) -> None:
@@ -52,3 +57,24 @@ class LumosWindow(Adw.ApplicationWindow):
         if self.ev_label:
             self.ev_label.set_label("{:.1f} EV".format(ev))
 
+    def onError(self, e: Exception):
+        self.lastError = e
+        self.error_banner.set_revealed(True)
+
+    @Gtk.Template.Callback()
+    def showErrorDetails(self, _button: Gtk.Button) -> None:
+        # Called by error_banner button click signal
+        if "ServiceUnknown" in self.lastError.message or "UnknownMethod" in self.lastError.message:
+            dialogTitle = "No light sensor found"
+        else:
+            dialogTitle = "Unable to access D-Bus"
+
+        dialog = Adw.AlertDialog(
+            heading = dialogTitle,
+            body = self.lastError,
+            close_response="close",
+        )
+        dialog.add_response("close", "Close")
+        dialog.choose(self, None, None)
+
+

src/window.ui

@@ -43,6 +43,15 @@
           <object class="GtkBox">
             <property name="orientation">1</property>
 
+            <!-- Errors banner -->
+            <child>
+              <object class="AdwBanner" id="error_banner">
+                <property name="title" translatable="true">Unable to access light sensor</property>
+                <property name="button-label" translatable="true">Details</property>
+                <signal name="button-clicked" handler="showErrorDetails"/>"
+              </object>
+            </child>
+
             <!-- Pages Stack -->
             <child>
               <object class="AdwViewStack" id="stack">