# A control implementing the UI
class Control
	super AppComponent

	# Direct parent `Control` in the control tree
	#
	# The parents (direct and indirect) receive all events from `self`,
	# like the `observers`.
	#
	# If `null` then `self` is at the root of the tree, or not yet attached.
	var parent: nullable CompositeControl = null is private writable(set_parent)

	# Direct parent `Control` in the control tree
	#
	# The parents (direct and indirect) receive all events from `self`,
	# like the `observers`.
	#
	# Setting `parent` calls `remove` on the old parent and `add` on the new one.
	fun parent=(parent: nullable CompositeControl)
	is autoinit	do
		var old_parent = self.parent
		if old_parent != null and old_parent != parent then
			old_parent.remove self
		end

		if parent != null then parent.add self

		set_parent parent
	end

	# Also notify the parents (both direct and indirect)
	redef fun notify_observers(event)
	do
		super

		var p = parent
		while p != null do
			p.on_event event
			p = p.parent
		end
	end
end