Class instantiation through mxml - setting properties

Question

Hi,
I'm trying to create a reusable component with an actionscript class.
I'd like to be able to set a handful of the class' properties withmxml attributes. So far, I've had no success doing so.
I've subset my problem into a separate, simplied project in an attempt to rule out any of the other parts of the real application interfering with what I'm attempting to accomplish. Unfortunately, my simplified project produces the same result.
In my example, I'm just trying to set value of the property "myValue."  Can anyone tell me what I'm doing wrong? What am I missing?
Thanks in advance for any help!
Main application (TestProj.mxml)
<?xml version="1.0" encoding="utf-8"?>
<s:Application xmlns:fx="http://ns.adobe.com/mxml/2009"
                  xmlns:s="library://ns.adobe.com/flex/spark"
                  xmlns:mx="library://ns.adobe.com/flex/mx"
                  minWidth="955" minHeight="600"
                  xmlns:pkg="pkg.*">
     <fx:Declarations>
          <!-- Place non-visual elements (e.g., services, value objects) here -->
     </fx:Declarations>
     <pkg:TestClass myvalue="some value" />
</s:Application>
Actionscript class (pkg\TestClass.as)
package pkg
     import mx.controls.Alert;
     import mx.core.UIComponent;
     public class TestClass extends UIComponent
          private var _myvalue:String;
          public function TestClass()
               Alert.show("myvalue=" + this._myvalue);     
          public function get myvalue():String
               return _myvalue;
          public function set myvalue(value:String):void
               _myvalue = value;

Answer 1

Hi,
The property gets set correctly, but the constructor of your class will always execute before the attributes - this is because Flex needs to create the instance and execute the c-tor before it can set the values on the instance.  Instead try something like this:
<pkg:TestClass id="foo" myvalue="some value" initialize="{Alert.show(foot.myvalue)}" />
This will execute the Alert.show when the component is being initialized.  If you need to put some init code in the component itself and that code relies on values set in MXML, then you can override UIComponent's public function initialize():void.
-Evtim