Question

im a newbie in flex. Im have a question 🙂

I have

[Bindable] 
          private var model:AlgorithmModel = new AlgorithmModel(); 
          private var serviceProxy:Algorithm = new Algorithm( model ); 

In MXML

                    private function Show():void
        {

            // now model.Solve_SendResult = null
            while(i<model.Solve_SendResult.length) //
            {
                Draw(); //draw cube
            }
        }
                    private function Solve_Click():void
        {
            //request is a array
            Request[0] = 2;
            Request[1] = 2;
            Request[2] = 3;
            serviceProxy.Solve_Send(request);

            Show();

        }
<s:Button x="386" y="477" label="Solve" click="Solve_Click();"/>

And when i call serviceProxy.Solve_Send(request); with request is array and i want use model.Solve_SendResult in my code flex to draw many cubes use papervison3d but in the first time i received model.Solve_SendResult = null . But when I click again then everything OK.

Anyone help me? Thanks?

Answer 1

The model.Solve_SendResult object contains a result of the executed serviceProxy.Solve_Send(request) method. The Solve_Send will be executed asynchronously and as a result, at the moment when you fire the show method the Solve_SendResult object may be still null.

As a solution, you can use the following:

1. Create a custom event

   package foo
   {
   import flash.events.Event;
   
   public class DrawEvent extends Event
   {
   public static const DATA_CHANGED:String = "dataChanged";
   
   public function DrawEvent(type:String, bubbles:Boolean=false, cancelable:Boolean=false)
   {
       super(type, bubbles, cancelable);
   }
   }
   }
   

2. In your Algorithm class define the following:

   [Event(name=DrawEvent.DATA_CHANGED, type="foo.DrawEvent")] 
   public class Algorithm extends EventDispatcher{ 
   //your code
   

3. In the Solve_SendHandler method of the Algorithm class add the following

   public virtual function Solve_SendHandler(event:ResultEvent):void
   {
   dispatchEvent(new DrawEvent(DrawEvent.DATA_CHANGED));
   //your code
   }
   

4. In your MXML class create onLoad method and add an event listener to an instance of the Algorithm class as it shown below:

   <mx:Application xmlns:mx="http://www.adobe.com/2006/mxml" layout="absolute" initialize="onLoad()">
   
   public function onLoad():void
   {
      serviceProxy.addEventListener(DrawEvent.DATA_CHANGED, onDataChanged);
   }
   
   private function onDataChanged(event:DrawEvent):void{
   while(i<model.Solve_SendResult.length) //
       {
           Draw(); //draw cube
       }
    }
   

5. make the following changes in the Solve_Click() method:

   private function Solve_Click():void
   {
       //request is a array
       Request[0] = 2;
       Request[1] = 2;
       Request[2] = 3;
       serviceProxy.Solve_Send(request);
   }
   

That is it! So, basically the code above do the following: you added a listener to your service (algorithm class), and the listener is listening for the DrawEvent.DATA_CHANGED event. The DrawEvent.DATA_CHANGED will be dispatched when your client receive a result of the Solve_Send invocation. Thus, the onDataChanged will draw your cube or do whatever you want 🙂

The approach above is basic and you have to know how events work in flex and how you can deal with it. Additional information is available here:

http://livedocs.adobe.com/flex/3/html/help.html?content=createevents_3.html
http://livedocs.adobe.com/flex/3/html/help.html?content=events_07.html

Regards,
Cyril