com.facebook.litho.annotations

Annotation Type Param

@Retention(value=CLASS)
public @interface Param

Params can be used together with Event callbacks i.e. EventHandler. An argument in the event handler annotated with Param will add it in the generated Component. This will allow to pass relevant arguments to the event handler while dispatching events. This is especially useful when event handlers can be reused.

For Example:

 @LayoutSpec
 class FacePileComponentSpec {

   @OnCreateLayout
   static Component onCreateLayout(
       ComponentContext c,
       @Prop Uri[] faces) {

     Component.Builder builder = Column.create(c);
     for (Uri face : faces) {
       builder.child(
           FrescoVitoImage2.create(c)
               .uri(face)
               .clickHandler(FacePileComponent.onFaceClicked(c, face)));
     }

     return builder.build();
   }

   @OnEvent(ClickEvent.class)
   static void onFaceClicked(
       ComponentContext c,
       @Param Uri face) {

     // Use the param face here
     Log.d("FacePileComponent", "Face clicked: " + face);
   }
 }