Add druid events in components

druid/base/back_handler.lua

@@ -1,6 +1,7 @@
 --- Component to handle back key (android, backspace)
 -- @module druid.back_handler
 
+local Event = require("druid.event")
 local const = require("druid.const")
 local component = require("druid.component")
 
@@ -15,6 +16,8 @@ local M = component.create("back_handler", { const.ON_INPUT })
 function M.init(self, callback, params)
 	self.callback = callback
 	self.params = params
+
+	self.on_back = Event(callback)
 end
 
 
@@ -24,7 +27,7 @@ end
 -- @tparam table action on_input action
 function M.on_input(self, action_id, action)
 	if action_id == const.ACTION_BACK and action[const.RELEASED] then
-		self.callback(self:get_context(), self.params)
+		self.on_back:trigger(self:get_context(), self.params)
 		return true
 	end