how to work with event in Flex? - actionscript-3

Question

import flash.events.Event;
public class RequestEvent extends Event
{
public static const REQUEST:String = "request";
private var Results:Boolean;
public function get Results():Boolean
{
return _Results;
}
public function RequestEvent(Results:Boolean=false)
{
super(REQUEST);
Results = Results;
}
override public function clone():Event
{
return new RequestEvent(Results);
}
}
}
hi can some body explain why we are doing overridding of function clone and calling super(request), new in flex ........so don't mind.

Answer 1

One needs to implement the clone method just so that Flex could re-clone the event in the case when an event handler wishes to dispatch the same event again. Flex does provide a default implementation but one may override the method to clone the event differently, if need be.
As for calling the super method, you must call the super becasue you are extending the Event class. The type (in your case, REQUEST) must be a unique string that would uniquely identify the event to Flex platform.
Hope it helps
Regards.

Answer 2

The question about the overriding of the clone method in custom events is very popular and it seems to be one of the Flex strange things. You can read about it here.
So you have to override this method and only in this method you can define values of custom properties. The method is not usual, so if you try to debug it you will never get the debugger in its body.
If you try to define the value of your custom property in the constructor, the value will be ignorred.
It can be unpractical to use a constant string as the event's type value. In this case all instances of your RequestEvent are of the same type and you could not tell them appart using in different situations. As you can see in the example below, this string is used in action listener to map the listener function.
In this example I have three buttons with different events - normal Event, my version of RequestEvent and your version of it. Have a look at it, I hope it can help to understand the case.
//Application
<fx:Script>
<![CDATA[
import fld02.com.customevent.RequestEvent;
import fld02.com.customevent.RequestEvent2;
import mx.controls.Alert;
private function onCustomGroupBtn2Clicked(evt:RequestEvent):void
{
Alert.show('Btn2Clicked: results = ' + evt.results.toString(), 'This is RequestEvent');
}
private function onCustomGroupBtn3Clicked(evt:RequestEvent2):void
{
Alert.show('Btn3Clicked: Results = ' + evt.Results.toString(), 'This is your RequestEvent');
}
]]>
</fx:Script>
<customevent:CustomGroup
BUTTON1_CLICKED="{Alert.show('Btn1Clicked', 'This is Event')}"
BUTTON2_CLICKED="onCustomGroupBtn2Clicked(event)"
request="onCustomGroupBtn3Clicked(event)"/>
</s:Application>
//CustomGroup
<?xml version="1.0" encoding="utf-8"?>
<s:Group xmlns:fx="http://ns.adobe.com/mxml/2009"
xmlns:s="library://ns.adobe.com/flex/spark"
xmlns:mx="library://ns.adobe.com/flex/mx" width="346" height="144">
<fx:Metadata>
[Event(name="BUTTON1_CLICKED", type="flash.events.Event")]
[Event(name="BUTTON2_CLICKED", type="fld02.com.customevent.RequestEvent")]
[Event(name="request", type="fld02.com.customevent.RequestEvent2")]
</fx:Metadata>
<fx:Script>
<![CDATA[
private function onBtn1Click():void
{
this.dispatchEvent(new Event("BUTTON1_CLICKED"));
}
private function onBtn2Click():void
{
var requestEvent:RequestEvent = new RequestEvent("BUTTON2_CLICKED");
requestEvent.results = true;
this.dispatchEvent(requestEvent);
}
]]>
</fx:Script>
<s:Button x="43" y="31" width="183" label="Generate Event" click="onBtn1Click()"/>
<s:Button x="43" y="62" width="183" label="Generate RequestEvent" click="onBtn2Click()"/>
<s:Button x="43" y="93" width="183" label="Generate Your RequestEvent" click="{this.dispatchEvent(new RequestEvent2(true))}"/>
</s:Group>
//My RequestEvent
package fld02.com.customevent
{
import flash.events.Event;
public class RequestEvent extends Event
{
private var _results:Boolean;
public function RequestEvent(type:String, bubbles:Boolean=false, cancelable:Boolean=false)
{
super(type, bubbles, cancelable);
}
override public function clone():Event
{
var requestEvent:RequestEvent = new RequestEvent(this.type);
requestEvent.results = this.results;
return requestEvent;
}
public function get results():Boolean
{
return _results;
}
public function set results(value:Boolean):void
{
_results = value;
}
}
}
//Your RequestEvent
package fld02.com.customevent
{
import flash.events.Event;
public class RequestEvent2 extends Event
{
public static const REQUEST:String = "request";
public function RequestEvent2(Results:Boolean=false)
{
super(REQUEST);
Results = Results;
}
private var _Results:Boolean;
public function get Results():Boolean
{
return _Results;
}
override public function clone():Event
{
return new RequestEvent2(Results);
}
}
}