Understanding AS3 custom events

核心提示：Every AS3 programmer uses event listeners to allow objects to become active and listen for specific instructions, such as a mouse click or the beginning of a ne

Every AS3 programmer uses event listeners to allow objects to become active and listen for specific instructions, such as a mouse click or the beginning of a new frame.

Now it’s time to see how can you create new events, but before entering into this script, let me say it’s not a “do it or die” feature.

You can always perform some if... then... else and achieve the same result, but from a PROgrammer point of view, a code with listeners is more readable than a complex list of conditions to check for events.

In this script, we are counting the time passed like in Understanding AS3 Timer Class, but we want to create a custom event to be triggered every 5 seconds.

Obviously in this case it’s quite pointless to create a custom event, but I am showing you the way you can do it.

This is the script:

package　{
　import　flash.display.Sprite;
　import　flash.events.Event;
　import　flash.events.TimerEvent;
　import　flash.utils.Timer;
　import　flash.text.TextField;
　public　class　dispatch　extends　Sprite　{
　　var　dispatcher:time_dispatcher　=　new　time_dispatcher();
　　var　time_count:Timer=new　Timer(1000);
　　var　interval_timer:TextField　=　new　TextField();　　　
　　public　function　dispatch()　{
　　　interval_timer.x=5;
　　　interval_timer.y=5;
　　　addChild(interval_timer);　　　
　　　time_count.addEventListener(TimerEvent.TIMER,show_time);
　　　dispatcher.addEventListener(time_dispatcher.ON_DIV_BY_FIVE,　on_event_triggered);
　　　time_count.start();
　　}
　　private　function　on_event_triggered(event:Event):void　{
　　　interval_timer.text="TRIGGERED";
　　}
　　function　show_time(event:TimerEvent)　{
　　　interval_timer.text=event.target.currentCount;
　　　dispatcher.check_division(event.target.currentCount);
　　}
　}
}
　
import　flash.events.EventDispatcher;
import　flash.events.Event;
class　time_dispatcher　extends　EventDispatcher　{
　public　static　var　ON_DIV_BY_FIVE:String="can　be　divided";
　public　function　check_division(num):void　{
　　if　(num%5==0)　{
　　　dispatchEvent(new　Event(time_dispatcher.ON_DIV_BY_FIVE));
　　}
　}
}

Line 8: Creating a new dispatcher, aggregating an instance of time_dispatcher class. I included the class in the same file to make the tutorial easier to understand, but you can obviously have your new class in another .as file as usual.

Line 16: This is where add the listener… as you can see it’s the same syntax you are used… except AS3 doesn’t have any ON_DIV_BY_FIVE listener.

The remaining lines are quite the same you’ve seen a thousand times, excluded line 24 where you can for check_division function that will trigger the event if the number of elapsed seconds can be divided by 5.

Line 35: This is how we fire, or dispatch, an event.

As I said, you can always use your if... then statement but in my opinion a code with listeners such as ON_LEVEL_COMPLETED is more readable than something like if(collected_items==total_items && time_left>0){...

This is the result of the script:

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