Event Handling

An .NET event, EventHandler and EventArgs inspired event handling system.

Examples

The following example constructs an Event and two handles to it. It invokes the event through one of the handles (de-registering it), then on the event itself.

use event_handler::prelude::*;
use std::sync::{Arc, Mutex};

#[test]
fn it_works() {
    // The values we want to mutate.
    // These need to be Send such that the handle functions can update them.
    let value = Arc::new(Mutex::new(0));
    let value2 = Arc::new(Mutex::new(0));

    // Create an event handler.
    let event = Event::new();

    // Create a closure to mutate the value.
    let update_first_value = {
        let first_value = value.clone();
        move |amount| *first_value.lock().unwrap() = amount
    };

    // Create a closure to mutate the other value.
    let update_second_value = {
        let second_value = value2.clone();
        move |amount| *second_value.lock().unwrap() = amount * 2
    };

    // Register the function to the event.
    let handle = event.add_fn(update_first_value).unwrap();
    let _handle = event.add_fn(update_second_value).unwrap();

    // Two handlers are now registered.
    assert_eq!(event.len(), 2);

    // Invoke the event on the handle.
    // Since we move the handle, this will de-register the handler when the scope is left.
    assert!(std::thread::spawn(move || { handle.invoke(41) })
        .join()
        .is_ok());
    assert_eq!(event.len(), 1);
    assert_eq!(*value.lock().unwrap(), 41);
    assert_eq!(*value2.lock().unwrap(), 41 * 2);

    // Invoke the event on the event itself.
    event.invoke(42);
    assert_eq!(*value.lock().unwrap(), 41);         // previous value
    assert_eq!(*value2.lock().unwrap(), 42 * 2);    // updated value
}

If the Event is dropped, calls to EventHandle::invoke will return an error.

use event_handler::prelude::*;
use std::sync::{Arc, Mutex};

#[test]
fn it_works() {
    let event = Event::new();

    // Register the function to the event.
    let value = Arc::new(Mutex::new(0));
    let handle = event.add_fn({
        let value = value.clone();
        move |amount| *value.lock().unwrap() = amount
    }).unwrap();

    // Register another function.
    let value2 = Arc::new(Mutex::new(0));
    let late_handle = event.add_fn({
        let value = value2.clone();
        move |amount| *value.lock().unwrap() = amount * 2
    }).unwrap();

    // Invoke the event on the handler itself.
    // This will move the event, dropping it afterwards.
    assert!(std::thread::spawn(move || {
        event.invoke(42);
    })
        .join()
        .is_ok());
    assert_eq!(*value.lock().unwrap(), 42);
    assert_eq!(*value2.lock().unwrap(), 42 * 2);

    // This event invocation will fail because the event is already dropped.
    assert_eq!(
        std::thread::spawn(move || { late_handle.invoke(41) })
            .join()
            .unwrap(),
        Err(EventInvocationError::EventDropped)
    );
}