--- ~~Title: Events Programming Guide in C#~~ ~~NOCACHE~~ --- # Events Programming Guide in C# # EFL is event-driven. This means that execution usually takes place within an internal EFL *Main Loop*. The application receives notifications through function callbacks. These can apply to virtually any event which occurs on a computer. Events play a central role in EFL. In this guide, you'll learn more about the required methods to handle them. You can also find usage examples in the [EFL examples repository](https://git.enlightenment.org/enlightenment/examples). | | WARNING | | | --- | ------- | --- | | ![NOTE](/_media/note-important.png) | **Some C# classes are currently in BETA state**
They should only be used for experimenting and **NOT** for any product development.
These classes are marked as **BETA** in the reference documentation.
The source code for the tutorials is subject to change in the future. | ![NOTE](/_media/note-important.png) | ## Listening to Events from Objects ## All EFL objects can emit events. You can discover more about them in the **Events** section of their respective [API Reference documentation](/develop/api/) (only in C, C# *coming soon*). In C#, you register a callback method for a given event by using the `+=` operator: ```csharp object.event += callback; ``` Substitute *object* with any EFL object and *event* with the identifier of the event (such as ``PollHighEvt`` or ``TickEvt``). Set *callback* to the method to be invoked when the event occurs. The method signature for the callback is: ```csharp void callback(object sender, EventArgs e); ``` *sender* is the object that emitted the event and *e* contains any additional information that the event sent. Events emitting additional information require that you use their own *EventArgs* class, for example, `Efl.Input.InterfaceKeyDownEvt_Args` when connecting to the `Efl.Input.Interface.KeyDownEvt` event. > **NOTE:** > The [API Reference documentation](/develop/api/) for each event tells you what type to cast *e* to (*Not available for C# yet*). > See [EFL_EVENT_POINTER_DOWN](/develop/api/efl/input/interface/event/pointer_down) for example. To stop receiving notifications for a particular event, unregister the callback using the `-=` operator: ```csharp object.event -= callback; ``` Note that in order to unregister the callback you have to provide the callback method again. This is because you can register different callback methods for the same event. ## Pausing and Resuming Event Notifications ## All event emissions from a given object can be paused (*frozen*) using `FreezeEvent()` and resumed with `ThawEvent()`: ```csharp object.FreezeEvent(); object.ThawEvent(); ``` While an object is frozen, only high-priority events (marked as *hot* in the documentation) will be emitted. Hot events cannot be stopped. Remember that ALL events emitting from a object are stopped if it's frozen, except for hot events. If you need to stop individual events you can unregister their callback temporarily and then re-register later. ## Example ## Below is the `core_event.cs` example taken from [the examples repository](https://git.enlightenment.org/enlightenment/examples/src/branch/master/reference/csharp/core/src/core_event.cs): ```csharp public class Example { // Polling callback private static void PollCb(object sender, EventArgs e) { Console.WriteLine(" Poll from {0}", ((Efl.Object)sender).GetName()); } public static void Main() { // Initialize EFL and all UI components Efl.All.Init(); // Retrieve the application's main loop var mainloop = Efl.App.AppMain; mainloop.SetName("Mainloop"); // This event gets triggered continuously mainloop.PollHighEvt += PollCb; // This timer will control events fired by the main loop var timer = new Efl.LoopTimer(mainloop, 0.1); timer.SetName("Timer"); // To count number of timer triggers int tick_count = 0; timer.TickEvt += (object sender, EventArgs e) => { string message = "Tick {0} from {1}: "; // Depending on the number of timer ticks, it does a different thing switch (tick_count) { case 0: message += "Freezing Mainloop events"; mainloop.FreezeEvent(); break; case 1: message += "Thawing Mainloop events"; mainloop.ThawEvent(); break; default: message += "Quitting"; mainloop.Quit(new Eina.Value(0)); break; } Console.WriteLine(message, tick_count, ((Efl.Object)sender).GetName()); tick_count++; }; Console.WriteLine("Waiting for Timer to call back..."); // Start the EFL main loop (and the experiment) mainloop.Begin(); // Shutdown EFL Efl.All.Shutdown(); Console.WriteLine("Application is over"); } } ``` A handler is connected to the `PollHighEvt` event of the application's main loop, which triggers continuously, at an undefined frequency of several shots per second (See the [Main Loop Programming Guide](main-loop.md)). At every shot, a line is printed on the console. At the same time, a timer is instantiated, firing every 100ms, which does a different thing at every shot: * First it freezes (pauses) all main loop events (except hot ones). * Then it thaws (resumes) all main loop events. * Finally, it quits the application. When you run the application, it should produce something like this on the console: ``` Waiting for Timer to call back... Poll from Mainloop Poll from Mainloop Poll from Mainloop Poll from Mainloop Poll from Mainloop Poll from Mainloop Tick 0 from Timer: Freezing Mainloop events Tick 1 from Timer: Thawing Mainloop events Poll from Mainloop Poll from Mainloop Poll from Mainloop Poll from Mainloop Poll from Mainloop Poll from Mainloop Tick 2 from Timer: Quitting ``` As you can see, the line `Poll from Mainloop` is printed continuously except in the period between Tick 0 and Tick 1 of the Timer, where main loop events are frozen. The exact amount of `Poll from Mainloop` messages you get depends on the frequency of the `PollHighEvt` event, which is chosen by EFL. The important thing is that there should be no such messages in between timer ticks 0 and 1, since main loop events are frozen. ## Further Reading ## [`core_event.cs` example](https://git.enlightenment.org/enlightenment/examples/src/branch/master/reference/csharp/core/src/core_event.cs) : C# Source code for this example. [`Efl.Object` API Reference](https://www.enlightenment.org/develop/api/efl/object) : Detailed documentation for the EFL object, which implements the events mechanism.