This library brings the principle of Events/Hooks to Arduino. In short, it allows a user to respond to certain "events" quite easily.

• Installation
• Usage
• Timed Events
• Event Arguments
• Limitations

1. Installation

Download the Event.cpp & Event.h file and move it to your Arduino sketch repository. Once this is done, include the library in your sketch.

#include "Event.h"

2. Usage

First off, we need to initialize a new EventManager. The EventManager will be responsible for registering new subscribers and triggering events when they occur.

EventManager evtManager;

Now that we have a new EventManager. Let's start listening for a new event.

EventManager evtManager;

void setup() 
{
	evtManager.subscribe(Subscriber("led.on", &LEDListener));
}

Notice that we use a reference to a listener as our "callback". So we would need to create this callback. The callback struct needs to extend the EventTask interface.

EventManager evtManager;
int ledPin = 12;

struct LEDListener : public EventTask
{
  using EventTask::execute;
  
  void execute(Event evt)
  {
  	digitalWrite(ledPin, HIGH);
  }

} LEDListener;

void setup() 
{
	pinMode(ledPin, OUTPUT);
	evtManager.subscribe(Subscriber("led.on", &LEDListener));
}

Now that we have a new listener registered for the event "led.on", we actually need to send a signal to trigger the event.

EventManager evtManager;
int ledPin = 12;

struct LEDListener : public EventTask
{
  using EventTask::execute;
  
  void execute(Event evt)
  {
  	digitalWrite(ledPin, HIGH);
  }

} LEDListener;

void setup() 
{
	pinMode(ledPin, OUTPUT);
	evtManager.subscribe(Subscriber("led.on", &LEDListener));
}

void loop()
{
	Event ledEvent = new Event("led.on");
	evtManager.trigger(ledEvent);
}

There we go, an event to light the LED at pin 12 triggers every "loop" interval. This might seem a bit redundant, but it's just an example. Event's won't be of much use for small applications with one purpose, they do however make large applications with many commands easier to maintain.

3. Timed Events

You can set up intervals to trigger certain events every X amount of milliseconds.

void setup()
{
	Event keepAlive = Event("event.keepAlive");
  evtManager.triggerInterval(TimedTask(2000, keepAlive));  
}

void loop()
{
  evtManager.tick();
}

This piece of code will set up the EventManager to trigger a new "event.keepAlive" event every 2000 milliseconds (2 seconds). You must call the tick() function, so that the event manager knows where in time it is.

4. Event Arguments

You can also use one event to do multiple things. Let's say we want one LED event to either turn it on or off.

...


struct LEDListener : public EventTask
{
  using EventTask::execute;
  
  void execute(Event evt)
  {
  	String extra = evt.extra;

  	if (extra == "on")
  	{
  		digitalWrite(ledPin, HIGH);
  	}
  	else
  	{
  		digitalWrite(ledPin, LOW);
  	}
  }

} LEDListener;

...

void loop()
{
	Event ledEvent = new Event("led.on", "on");
	evtManager.trigger(ledEvent);

	delay(1000);

	Event ledEvent = new Event("led.on", "off");
	evtManager.trigger(ledEvent);

	delay(1000);
}

This will turn raise a new "on" event and one second after that, raise an event to turn the LED off again. Thus, this will result in a "blinking LED" sketch.

5. Limitations

This library was mainly written for programming with the Arduino UNO. Since it has limited memory, there is a hardcoded limit on the amount of events.

TimedTask _interval[5]; // 5 available interval slots
Subscriber _sub[10]; // 10 available subscriber slots

This can be changed in the Event.h header file.