Events (UserEvent)

The UserEvent class can be used to emit messages (events) from a component (ux:Class) to the outside world. These messages (events) can be handled in UX markup and/or JavaScript.

Creating events

To create an event, place a UserEvent at the root of our component class to indicate that it can raise a particular event.

Where we place our UserEvent is important, since only the node it is attached to and its children can raise or handle it.

<Panel ux:Class="MyComponent">
	<UserEvent ux:Name="myEvent" />
</Panel>
	

This creates an event named myEvent, specific to the MyComponent class

App-global events

To make a UserEvent that can be raised or handled from anywhere in the app, we simply make the event part of the App-component, by declaring it on the root App node, like this:

<App>
 	<UserEvent ux:Name="myGlobalEvent" />

 	<!-- The rest of our app goes here -->

</App>

Raising events

We can raise events from JavaScript using the .raise() method on the UserEvent object:

<Panel ux:Class="MyComponent">
	<UserEvent ux:Name="myEvent" />
	
	<JavaScript>
		setTimeout(function() {
			myEvent.raise();
		}, 5000);
	</JavaScript>
</Panel>

You can pass arguments when raising an event.

myEvent.raise({
	userName: "james",
	isAdmin: false
});

Responding to events

We respond to events using the OnUserEvent trigger. We can use this trigger to perform UX actions or animators in response like any other trigger:

<MyComponent>
	<OnUserEvent EventName="myEvent">
		<!-- Actions/animators go here -->
	</OnUserEvent>
</MyComponent>

Note that we are referencing our UserEvent by name even though it is declared outside of our current scope. We can do this because EventName refers to the Name of the event. The actual instance of UserEvent will be resolved at runtime.

Alternatively, we can use the Handler event to pass the event into JavaScript:

<JavaScript>
	function eventHandler() {
		//do something
	}
	
	module.exports = { eventHandler: eventHandler };
</JavaScript>

<MyComponent>
	<OnUserEvent EventName="myEvent" Handler="{eventHandler}"/>
</MyComponent>

Any arguments are passed to the JavaScript event handler as part of the first argument object:

<JavaScript>
	function eventHandler(args) {
		console.log("Username: " + args.userName + ", Is admin: " + args.isAdmin);
	}
	
	module.exports = { eventHandler: eventHandler };
</JavaScript>

<OnUserEvent EventName="myEvent" Handler="{eventHandler}" />

Raising events from UX alone

We can alternatively use the RaiseUserEvent to raise the event from UX without using JavaScript, and even pass arguments using the UserEventArg class:

<Panel ux:Class="MyComponent">
	<UserEvent ux:Name="myEvent" />
	
	<Clicked>
		<RaiseUserEvent EventName="myEvent">
			<UserEventArg Name="userName" StringValue="james" />
			<UserEventArg Name="isAdmin" BoolValue="false" />
		</RaiseUserEvent>
	</Clicked>
</Panel>

Creating custom triggers based on events

When creating reusable components, can subclass the OnUserEvent class to make new triggers the user of our components can use. This allows for better abstraction, as the user doesn't need to know you were using the UserEvent system at all, nor the internal name of your event. You are then free to refactor the implementation of your component later.

<OnUserEvent ux:Class="SomethingHappened" EventName="myEvent" />

The user can then use this pattern instead:

<MyComponent>
	<SomethingHappened Handler="{handleStuff}" />
</MyComponent>