createChildren Called Before Component's MXML Bracket Logic Is Evaluated

I have the following MXML:

<mx:Script>
    var someBoolean:Boolean = determineSomeCondition();
</mx:Script>

....

<foo:MyComponent somePropertyExpectingIDataRenderer="{
                                    someBoolean
                                    ? new Component1ThatImplementsIDataRenderer()
                                    : new Component2ThatImplementsIDataRenderer()
                                                     }">        
</foo:MyComponent>

I have also overridden the 开发者_如何学编程createChildren() function:

override protected function createChildren():void {
    super.createChildren();

    //do something with somePropertyExpectingIDataRenderer
}

My problem is: createChildren() is being called before the squiggly bracket logic is being evaluated, so in createChildren(), somePropertyExpectingIDataRenderer is null.

However if I pass the component via MXML like this:

<foo:MyComponent>
    <bar:somePropertyExpectingIDataRenderer>
        <baz:Component1ThatImplementsIDataRenderer/>
    </bar:somePropertyExpectingIDataRenderer>
</foo:MyComponent>

Then when createChildren() is called, that same property isn't null. Is this supposed to happen and if so, what other workarounds should I consider?

You have to wait until your component goes through the first invalidation phase in order to get access to the default value setted in your MXML. This happens just after createChildren() has been called, when the initialize event of your component has been dispatched.

Here is how I would do it :

public function set myProperty(value:IDataRenderer):void
{
    if (_myProperty != value)
    {
        myPropertyChanged = true;
        _myPropert = value;
        invalidateDisplayList();
    }
}



protected override function updateDisplayList(unscaledWidth:Number,
                                              unscaledHeight:Number):void
{
    super.updateDisplayList(unscaledWidth, unscaledHeight);

 ...

    if (myPropertyChanged )
        doWhateverYouNeedToDo(); 



}

(Of course, this example supposes changing your property needs a redrawing)