Create Custom Application Events
Use type="APPLICATION" in the <aura:event> tag for an application event. For example, this c:appEvent application event has one attribute with a name of message.
<!--c:appEvent-->
<aura:event type="APPLICATION">
<!-- Add aura:attribute tags to define event shape.
One sample attribute here. -->
<aura:attribute name="message" type="String"/>
</aura:event>
The component that fires an event can set the event’s data. To set the attribute values, call event.setParam() or event.setParams(). A parameter name set in the event must match the name attribute of an <aura:attribute> in the event. For example, if you fire c:appEvent, you could use:
event.setParam("message", "event message here");
The component that handles an event can retrieve the event data. To retrieve the attribute in this event, call event.getParam("message") in the handler’s client-side controller.