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package com.senocular.events {
import flash.display.DisplayObject;
import flash.events.Event;
import flash.events.EventDispatcher;
import flash.utils.Dictionary;
/**
* StageDetection
* Lets a DisplayObject know when its been added to
* a display list attached to the stage.
*
* Usage:
* // used in the constructor where addedToStage and removedFromStage
* // are event handler methods
* var stageDetect:StageDetection = new StageDetection(this);
* stageDetect.addEventListener(StageDetection.ADDED_TO_STAGE, addedToStage);
* stageDetect.addEventListener(StageDetection.REMOVED_FROM_STAGE, removedFromStage);
*/
public class StageDetection extends EventDispatcher {
protected var target:DisplayObject;
protected var parents:Dictionary;
protected var detect:String;
public static const ADDED_TO_STAGE:String = "addedToStage";
public static const REMOVED_FROM_STAGE:String = "removedFromStage";
/**
* Constructor
*/
public function StageDetection(targetObject:DisplayObject) {
target = targetObject;
// determine whether need to detect for added or removed
detect = (target.stage == null) ? Event.ADDED : Event.REMOVED;
// update parent listeners for detect events
updateListeners();
}
/**
* updates listeners from which ADDED and REMOVED events are to be received
*/
protected function updateListeners(newDetect:String = null):void {
// cleanup old listeners in parents
if (parents) {
for (var key:Object in parents) {
key.removeEventListener(detect, stageCheck, false);
}
}
// new event to detect if given
if (newDetect) detect = newDetect;
// set up detect event with current parents
parents = new Dictionary(true);
var parent:DisplayObject = target;
while (parent) {
parent.addEventListener(detect, stageCheck, false, 0, true);
parents[parent] = true;
parent = parent.parent;
}
}
/**
* event handler for ADDED and REMOVED events checking for stage access
*/
protected function stageCheck(evt:Event):void {
// only check for originating object
if (evt.target != evt.currentTarget) return;
// evt.type either ADDED or REMOVED
switch(evt.type) {
// parent added to another display object
case Event.ADDED:
// stage available, added to stage
if (target.stage != null) {
// added to stage, dispatch event, update
dispatchEvent(new Event(ADDED_TO_STAGE));
updateListeners(Event.REMOVED);
// stage inaccessible, added to some other display object not on stage
} else {
// display list has changed, update parent listeners
updateListeners();
}
break;
// parent removed from stage
case Event.REMOVED:
// removed from stage, dispatch event, update
dispatchEvent(new Event(REMOVED_FROM_STAGE));
updateListeners(Event.ADDED);
break;
}
}
}
}
