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tutorial:events [2019/07/03 00:29] – added javadoc description draylartutorial:events [2019/07/03 21:07] – Corrections and clarifications jamieswhiteshirt
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 ====== Custom Events ====== ====== Custom Events ======
-Events here, event there! Everyone and everything gets an event!+Fabric API provides an event system that allows mods to react to events in the game. The purpose of adding events is to add hooks that satisfy common use cases and/or providing enhanced compatibility and performance between mods that hook into the same areas of the code. The use of events often substitutes the use of mixins. Fabric API provides events for some use cases, but not all, meaning you'll have to use other methods like Mixins to add a hook. You can then choose to implement the hook as an event.
  
-Events are a formalized hook you can use to respond to actions in the game. They serve as a way to prevent 20 mixins in the same spot (because everyone wants to hook after the same thing). In this tutorial, we'll look at creating your own event which is triggered when sheep are sheared. The process of creating an event is:+In this tutorial, we'll look at creating your own event which is triggered when sheep are sheared. The process of creating an event is:
  
   * creating the event callback interface   * creating the event callback interface
-  * triggering the event from a mixin+  * triggering the event from a Mixin
   * creating a test implementation   * creating a test implementation
  
 ==== Creating a Callback Interface ==== ==== Creating a Callback Interface ====
-The callback interface is the core of your event. It stores a list of all registered listeners (which are like responses to an event), and calls them all when the action occurs. Each listener can then say "cancel this," "approve this," or "I don't care, leave it to the next guy," while doing whatever response they need to.+The callback interface describes what must be implemented by event listeners that will listen to your event. The callback interface also describes how the event will be called from our mixin. It is conventional to place an Event object as a field in the callback interface, which will identify our actual event. 
 + 
 +For our Event implementation we will choose to use an array backed event. The array will contain all event listeners that are listening to the event. Our implementation will call the event listeners in order until one of them does not return ''ActionResult.PASS''. This means that a listener can say "cancel this", "approve this" or "don't care, leave it to the next event listener" using its return value. Using ActionResult as a return value is a conventional way to make event handlers cooperate in this fashion.
  
 You'll need to create an interface that has an ''Event'' instance and method for response implementation. A basic setup for our sheep shear callback is: You'll need to create an interface that has an ''Event'' instance and method for response implementation. A basic setup for our sheep shear callback is:
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     for (SheepShearCallback event : listeners) {     for (SheepShearCallback event : listeners) {
 </code> </code>
-We then call our method (in this case, ''interact'') on the listener to get it's response:+We then call our method (in this case, ''interact'') on the listener to get its response:
 <code java [enable_line_numbers="false"]> <code java [enable_line_numbers="false"]>
 ActionResult result = event.interact(player, sheep); ActionResult result = event.interact(player, sheep);
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 </code> </code>
  
-==== Triggering the event from a mixin ====+==== Triggering the event from a Mixin ====
 We now have the basic event skeleton, but we need to trigger it. Because we want to have the event called when a player attempts to shear a sheep, we call the event invoker in ''SheepEntity#interactMob'' when ''dropItems()'' is called (ie. sheep can be sheared and player is holding shears): We now have the basic event skeleton, but we need to trigger it. Because we want to have the event called when a player attempts to shear a sheep, we call the event invoker in ''SheepEntity#interactMob'' when ''dropItems()'' is called (ie. sheep can be sheared and player is holding shears):
 <code java [enable_line_numbers="false"]> <code java [enable_line_numbers="false"]>
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 }); });
 </code> </code>
-Note that this event also sets the sheep to be sheared manually, as it is normally canceled if we return FAIL.+Note that this event also sets the sheep to be sheared manually, as it is normally canceled if we return FAIL. If you don't //need// to cancel the event, make sure you return ''PASS'' so other listeners are allowed to operate as well. Failing to follow these "not spoken rules" may result in angry modders on your doorstep.
  
 If you enter into your game and shear a sheep, a diamond should drop instead of wool. If you enter into your game and shear a sheep, a diamond should drop instead of wool.
 {{https://i.imgur.com/dG73Z6G.mp4?400|}} {{https://i.imgur.com/dG73Z6G.mp4?400|}}
tutorial/events.txt · Last modified: 2021/05/28 00:31 by 127.0.0.1