as3Signals初探

開發Flash或Flex系統時，覺得AS3內建的事件不甚好用嗎，那as3signals或許是一個不錯的解決方案。

AS3內建事件的相關評論，可參考：

• My Critique of AS3 Events - Part 1 
• My Critique of AS3 Events - Part 2 - The Dispatchening

as3Signals 是Robert Penner針對AS3內建的事件 (built-in events)，所提出的一種新架構，該架構簡化了物件(或元件)間透過事件溝通的程序。

as3Signals概念摘錄
  Signals: Think Outside the Event.

• Signals are light-weight, strongly-typed AS3 messaging tools.
• Wire your application with better APIs and less boilerplate than AS3 Events.

  Concept

• A Signal is essentially a mini-dispatcher specific to one event, with its own array of listeners.
• A Signal gives an event a concrete membership in a class.
• Listeners subscribe to real objects, not to string-based channels.
• Event string constants are no longer needed.
• Signals are inspired by C# events and signals/slots in Qt.

以一個簡單範例作說明，當Radio的massage屬性被設定訊息後，Radio會dispach事件，並由BroadcastListener進行監聽(listener)與回應。

一般寫法：
RadioEvent類別：必須自訂事件

package
{
    import flash.events.Event;

    public class RadioEvent extends Event 
    {
        public static const BROAD_CAST:String = "broadcast";
        public var message:String;
    
        public function RadioEvent(type:String, message:String, 
            bubbles:Boolean = false, cancelable:Boolean = false) 
        {
            super(type, bubbles, cancelable);
            this.message=message;
        }
    
        override public function clone():Event 
        {
            return new RadioEvent(this.type, this.message ,
                this.bubbles, this.cancelable);
        }
    }
}

Radio類別：dispatch event

package
{
    import flash.events.EventDispatcher;
    
    [Event(name="broadcast",type="RadioEvent")]
    
    public class Radio extends EventDispatcher 
    {
        public var eventObject:RadioEvent;
        private var _message:String;
        
        public function get message():String 
        { 
            return _message; 
        }
        
        public function set message(value:String):void
        {
            _message = value;
            eventObject=new RadioEvent("broadcast", _message);
            this.dispatchEvent(eventObject);
        }
    }    
}

BroadcastListener類別：listener

package
{
    public class BroadcastListener
    {    
        public function onBroadcastHandler(event:RadioEvent):void
        {
            trace('Heard message: ' + event.message);
        }
    }
}

SignalsHelloWorld類別：設定Radio物件的message屬性

package
{
    import flash.display.Sprite;
    
    public class SignalsHelloWorld extends Sprite
    {
        private var radio:Radio;
        private var broadcastListener:BroadcastListener;
    
        public function SignalsHelloWorld()
        {
            this.radio=new Radio();
            this.broadcastListener=new BroadcastListener();
            radio.addEventListener(RadioEvent.BROAD_CAST, 
            this.broadcastListener.onBroadcastHandler);
            radio.message="Hello World, Kolen!";                
        }
    }
}

使用as3signals的寫法：
SignalsRadio類別：透過Signal類別dispatch event

package
{
    import org.osflash.signals.Signal;
    
    public class SignalsRadio 
    {
        private var _message:String;
        public var broadcast:Signal;
        
        public function SignalsRadio()
        {
            broadcast = new Signal(String);
        }
        
        public function get message():String 
        { 
            return _message; 
        }
        
        public function set message(value:String):void
        {
            _message = value;
            broadcast.dispatch(_message);
        }
    }    
}

SignalsBroadcastListener類別：listener

package
{
    public class SignalsBroadcastListener
    {    
        public function onBroadcastHandler(message:String):void
        {
            trace('Heard message: ' + message);
        }
    }
}

SignalsHelloWorld類別：設定Radio物件的message屬性

package
{
    import flash.display.Sprite;
    
    public class SignalsHelloWorld extends Sprite
    {
        private var radio:SignalsRadio;
        private var broadcastListener:SignalsBroadcastListener;
        
        public function SignalsHelloWorld()
        {            
            this.radio=new SignalsRadio();
            this.broadcastListener=new SignalsBroadcastListener();
            radio.broadcast.add(this.broadcastListener.onBroadcastHandler);
            radio.message="Hello World, Kolen!";                
        }
    }
}

物件間的溝通是不是變簡單了呢，而本範例僅用到Signal類別，尚有DeluxeSignal、NativeSignal兩種類別，待後續再作介紹。

as3signals的學習資源

• robertpenner / as3-signals
• Robert Penner on Flash
• An introduction to AS3 Signals
• as3signals – An Awesome Solution to Events/Signals in AS3
• as3signals: new approach for AS3 Events