Event Dispatchers

• So far we have two ways for blueprints to talk to each other.
  1. We can search for all instances of a class and call a method or event.
     • But the documentation says this is expensive.
  2. We can have an instance recorded in a variable and call it.
• Event dispatchers give us a third option.
  • With an event dispatcher we can
    • Generate a special event
    • Have other blueprints subscribe to that event
  • This is still instance based, but now the client needs to know what server it is communicating with.
  • Ie no searching for all and no long lists of clients.
• Example 1, a broadcaster
  • In this example, an actor will "broadcast" when it is stepped on.
  • Other actors, "receivers" will register to receive broadcasts from that actor..
  • This is really a broadcast. The message is sent, those tuned in will hear it.
  • Application building alarm.
  • Create a blueprint actor, BP_Broadcast.
    • Add something to be visible and a collision box.
    • Add a EventSendMessage in the Event Dispatchers area.
    • Drag this onto the panel and select call
    • 
    • Connect this to on actor begin overlap.
    • 
  • Now, when this actor is overlapped, everyone who subscribes will receive an message
  • Place this in the scene.
  • Build an blueprint actor BP_Receiver
    • I added a sphere and a light
    • I added a variable of type BP_Broadcaster, called MySender.
    • This is who this blueprint will listen to.
    • Drag this variable onto the event graph and select Bind Event to Event Send Message
    • Hook This up to the EventBeginPlay event.
    • 
    • Add a custom event, GotMessage and hook this up to the bind node.
    • 
    • I added code to switch the lights on and off.
    • 
    • I added four of these to the scene and "tuned" them into the broadcaster by setting the variable to the broadcaster.
  • You can do this the other was as well
    • Create a central report station.
    • Think of this as a hall of records or a centralized log.
    • BP_Recorder
      • Create a event Dispatcher EventGotAReport
      • Drag this onto the event graph but this time select Assign
      • 
      • Connect this to the Begin Play event.
      • 
      • Build something to happen.
        • I added a string so as input so we can see who called us.
      • 
    • Compile and add it to the scene.
  • Finally, build a reporter class BP_Reporter
    • Make something to step on and detect collision
    • I added a variable, MyReport of type BP_Recorder
    • I added a string, "My Name".
    • Expose both of these variables.
    • Then in the event graph added the following
    •