Moved callbacks (which live in the top-level namespace) into a separate file, so I have a clear overview of all these.

src/App/App.cpp

@@ -9,7 +9,7 @@ namespace Dough
     }
 
     App::App() : config(),
-                 ui(),
+                 ui(onoffButtonInterruptCallback, setupButtonInterruptCallback),
                  wifi(),
                  mqtt(&wifi, mqttOnConnectCallback, mqttOnMessageCallback),
                  temperatureSensor(
@@ -32,9 +32,6 @@ namespace Dough
     void App::setup()
     {
         ui.setup();
-        ui.onoffButton.onInterrupt(::onoffButtonInterruptCallback);
-        ui.setupButton.onInterrupt(::setupButtonInterruptCallback);
-
         wifi.setup();
         mqtt.setup();
         temperatureSensor.setup();
@@ -64,59 +61,3 @@ namespace Dough
         distanceSensor.clearHistory();
     }
 } // namespace Dough
-
-Dough::Logger callbackLogger("CALLBACK");
-
-void mqttOnConnectCallback(Dough::MQTT *mqtt)
-{
-    callbackLogger.log("s", "MQTT connection establish, subscribing to topics");
-    mqtt->subscribe("container_height");
-    mqtt->subscribe("temperature_offset");
-}
-
-void mqttOnMessageCallback(String &topic, String &payload)
-{
-    callbackLogger.log("ssss", "MQTT message received: ", topic.c_str(), " = ", payload.c_str());
-
-    if (topic.endsWith("/container_height"))
-    {
-        Dough::App::Instance()->config.setContainerHeight(payload.toInt());
-    }
-    else if (topic.endsWith("/temperature_offset"))
-    {
-        Dough::App::Instance()->config.setTemperatureOffset(payload.toInt());
-    }
-    else
-    {
-        callbackLogger.log("ss", "ERROR - Unhandled MQTT message, topic = ", topic.c_str());
-    }
-}
-
-void onoffButtonInterruptCallback()
-{
-    Dough::App::Instance()->ui.onoffButton.handleButtonState();
-}
-
-void setupButtonInterruptCallback()
-{
-    Dough::App::Instance()->ui.setupButton.handleButtonState();
-}
-
-void sensorOnMeasureCallback()
-{
-    Dough::App::Instance()->ui.notifySensorActivity();
-}
-
-void sensorOnPublishCallback()
-{
-    Dough::App::Instance()->ui.notifyNetworkActivity();
-}
-
-// This callback is called when the TC4 timer from the UI code hits an overflow
-// interrupt. It is defined outside the Dough namespace, because TC4_Handler is
-// a hard-coded root namespace function name.
-void TC4_Handler()
-{
-    Dough::App::Instance()->ui.updateLEDs();
-    REG_TC4_INTFLAG = TC_INTFLAG_OVF; // Clear the OVF interrupt flag.
-}

src/App/App.h

@@ -4,6 +4,7 @@
 #include <Arduino.h>
 #include "UI/UI.h"
 #include "App/Configuration.h"
+#include "App/callbacks.h"
 #include "Data/SensorController.h"
 #include "Sensors/TemperatureSensor.h"
 #include "Sensors/HumiditySensor.h"
@@ -34,12 +35,4 @@ namespace Dough
     };
 }
 
-// Callback functions that need to live in the global namespace.
-void mqttOnConnectCallback(Dough::MQTT *mqtt);
-void mqttOnMessageCallback(String &topic, String &payload);
-void onoffButtonInterruptCallback();
-void setupButtonInterruptCallback();
-void sensorOnMeasureCallback();
-void sensorOnPublishCallback();
-
 #endif

src/App/callbacks.cpp

@@ -0,0 +1,57 @@
+#include "App/callbacks.h"
+
+Dough::Logger callbackLogger("CALLBACK");
+
+void mqttOnConnectCallback(Dough::MQTT *mqtt)
+{
+    callbackLogger.log("s", "MQTT connection establish, subscribing to topics");
+    mqtt->subscribe("container_height");
+    mqtt->subscribe("temperature_offset");
+}
+
+void mqttOnMessageCallback(String &topic, String &payload)
+{
+    callbackLogger.log("ssss", "MQTT message received: ", topic.c_str(), " = ", payload.c_str());
+
+    if (topic.endsWith("/container_height"))
+    {
+        Dough::App::Instance()->config.setContainerHeight(payload.toInt());
+    }
+    else if (topic.endsWith("/temperature_offset"))
+    {
+        Dough::App::Instance()->config.setTemperatureOffset(payload.toInt());
+    }
+    else
+    {
+        callbackLogger.log("ss", "ERROR - Unhandled MQTT message, topic = ", topic.c_str());
+    }
+}
+
+void onoffButtonInterruptCallback()
+{
+    Dough::App::Instance()->ui.onoffButton.handleButtonState();
+}
+
+void setupButtonInterruptCallback()
+{
+    Dough::App::Instance()->ui.setupButton.handleButtonState();
+}
+
+void sensorOnMeasureCallback()
+{
+    Dough::App::Instance()->ui.notifySensorActivity();
+}
+
+void sensorOnPublishCallback()
+{
+    Dough::App::Instance()->ui.notifyNetworkActivity();
+}
+
+// This callback is called when the TC4 timer from the UI code hits an overflow
+// interrupt. It is defined outside the Dough namespace, because TC4_Handler is
+// a hard-coded root namespace function name.
+void TC4_Handler()
+{
+    Dough::App::Instance()->ui.updateLEDs();
+    REG_TC4_INTFLAG = TC_INTFLAG_OVF; // Clear the OVF interrupt flag.
+}

src/App/callbacks.h

@@ -0,0 +1,24 @@
+#ifndef DOUGH_APP_CALLBACKS_H
+#define DOUGH_APP_CALLBACKS_H
+
+#include "Network/MQTT.h"
+#include "UI/Logger.h"
+#include "App/App.h"
+
+// This header file defines various callback functions that
+// live in the global namespace. All callbacks are bundled here
+// to have a clear overview of them.
+
+// Callbacks from the Dough::MQTT module.
+void mqttOnConnectCallback(Dough::MQTT *mqtt);
+void mqttOnMessageCallback(String &topic, String &payload);
+
+// Callbacks from the Dough::UI module.
+void onoffButtonInterruptCallback();
+void setupButtonInterruptCallback();
+
+// Callbacks from the Dough::SensorController module.
+void sensorOnMeasureCallback();
+void sensorOnPublishCallback();
+
+#endif

src/UI/Button.cpp

@@ -9,19 +9,17 @@ namespace Dough
     // working. An interrupt service routine (ISR) function must be created
     // and linked to the button to get the interrupts working. Pattern:
     //
-    //   // Construct the button instance.
-    //   Button myButton(MYBUTTON_PIN);
-    //
     //   // A function for handling interrupts.
     //   void myButtonISR() {
     //       myButton.handleButtonState();
     //   }
     //
-    //   // Linking the function ot button interrupts.
-    //   myButton.onInterrupt(myButtonISR);
-    Button::Button(int pin)
+    //   // Construct the button instance.
+    //   Button myButton(MYBUTTON_PIN, myButtonISR);
+    Button::Button(int pin, ButtonISR isr)
     {
         _pin = pin;
+        attachInterrupt(digitalPinToInterrupt(_pin), isr, CHANGE);
     }
 
     void Button::setup()
@@ -29,30 +27,22 @@ namespace Dough
         pinMode(_pin, INPUT_PULLUP);
     }
 
-    // Assign an interrupt service routine (ISR) for handling button
-    // interrupts. The provided isr should relay interrupts to the
-    // handleButtonState() method of this class (see constructor docs).
-    void Button::onInterrupt(ButtonHandler isr)
-    {
-        attachInterrupt(digitalPinToInterrupt(_pin), isr, CHANGE);
-    }
-
     // Assign an event handler for short and long button presses.
     // When specific handlers for long and/or short presses are
     // configured as well, those have precedence over this one.
-    void Button::onPress(ButtonHandler handler)
+    void Button::onPress(ButtonISR handler)
     {
         _pressHandler = handler;
     }
 
     // Assign an event handler for long button presses.
-    void Button::onLongPress(ButtonHandler handler)
+    void Button::onLongPress(ButtonISR handler)
     {
         _longPressHandler = handler;
     }
 
     // Assign an event handler for short button presses.
-    void Button::onShortPress(ButtonHandler handler)
+    void Button::onShortPress(ButtonISR handler)
     {
         _shortPressHandler = handler;
     }

src/UI/Button.h

@@ -18,7 +18,7 @@ namespace Dough
         READY_FOR_NEXT_PRESS
     } ButtonState;
 
-    typedef void (*ButtonHandler)();
+    typedef void (*ButtonISR)();
 
     // This class provides a simple interface for handling button presses.
     // Only a few events are supported:
@@ -30,21 +30,20 @@ namespace Dough
     class Button
     {
     public:
-        Button(int pin);
+        Button(int pin, ButtonISR isr);
         void setup();
         void loop();
-        void onInterrupt(ButtonHandler isr);
-        void onPress(ButtonHandler handler);
-        void onShortPress(ButtonHandler handler);
-        void onLongPress(ButtonHandler handler);
+        void onPress(ButtonISR handler);
+        void onShortPress(ButtonISR handler);
+        void onLongPress(ButtonISR handler);
         void clearEvents();
         void handleButtonState();
 
     private:
         int _pin;
-        ButtonHandler _pressHandler = nullptr;
-        ButtonHandler _shortPressHandler = nullptr;
-        ButtonHandler _longPressHandler = nullptr;
+        ButtonISR _pressHandler = nullptr;
+        ButtonISR _shortPressHandler = nullptr;
+        ButtonISR _longPressHandler = nullptr;
         bool _debounceState = false;
         unsigned long _debounceTimer = 0;
         ButtonState _state = UP;

src/UI/UI.cpp

@@ -2,8 +2,10 @@
 
 namespace Dough
 {
-    UI::UI() : onoffButton(ONOFF_BUTTON_PIN),
-               setupButton(SETUP_BUTTON_PIN),
+    UI::UI(
+        ButtonISR onoffButtonISR,
+        ButtonISR setupButtonISR) : onoffButton(ONOFF_BUTTON_PIN, onoffButtonISR),
+                                    setupButton(SETUP_BUTTON_PIN, setupButtonISR),
                                     _ledBuiltin(LED_BUILTIN),
                                     _led1(LED1_PIN),
                                     _led2(LED2_PIN),

src/UI/UI.h

@@ -14,10 +14,8 @@ namespace Dough
     class UI
     {
     public:
-        UI();
+        UI(ButtonISR onoffButtonISR, ButtonISR setupButtonISR);
         void setup();
-        static void onoffButtonISR();
-        static void setupButtonISR();
         Button onoffButton;
         Button setupButton;
         void processButtonEvents();