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/**
* Represents an event.
* Events enable a class or object to notify other classes or objects when something of interest occurs.
* The class that sends (or invokes) the event is called the publisher and the classes that receive (or handle) the event are called subscribers.
*
* Objects can create an instances of an Events and offer that Events for other objects to attach to.
* Objects who want to be informed about an Event can attach a function (an event handler) to the event which is then called when the event is fired.
*
* @template TEventArg Type of the event argument. Use void if the event does not has an argument.
*/
export class Event<TEventArg> {
/**
* Creates a new instance of the Event class.
*/
constructor() {
this.eventHandlers = new Array<(arg: TEventArg) => void>();
}
/**
* Adds an event handler to this event, so that when the event is fired the given event handler function is called.
*
* @param eventHandler The event handler function to add to this event.
* @throws {Error} Thrown if the given event handler function has already been added to this event.
*/
public addHandler = (eventHandler: (arg: TEventArg) => void): void => {
if (this.eventHandlers.indexOf(eventHandler) > -1) {
throw new Error("The given event handler is already added to this event.");
}
this.eventHandlers.push(eventHandler);
}
/**
* Removes an event handler from this event, so that the given event handler function will not be called anymore when the event is fired.
*
* @param eventHandler: The event handler function to remove.
* @throws {Error} Thrown if the given event handler function has not been added to this event before.
*/
public removeHandler = (eventHandler: (arg: TEventArg) => void): void => {
const index = this.eventHandlers.indexOf(eventHandler);
if (!(index > -1)) {
throw new Error("The given event handler has not been added to this event yet.");
}
this.eventHandlers.splice(index, 1);
}
/**
* Invokes the event and calls all event handler functions currently registered on the event.
*
* @param argument The argument for the event. The argument will be passed to all registered event handler functions.
*/
public invoke = (argument?: TEventArg): void => {
this.eventHandlers.forEach((eventHandler: (arg?: TEventArg) => void, index: number, array: Array<(arg: TEventArg) => void>): void => {
eventHandler(argument);
});
}
private eventHandlers: Array<(arg?: TEventArg) => void>;
}
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