Why does BindingUtils.bindProperty() not work immediately?

I have a two way binding between a loaded flash file and the main application in flex.

    BindingUtils.bindProperty(this, "micGainValue", audioPublisherApp, "micVolume");
    BindingUtils.bindProperty(audioPublisherApp, "micVolume", this, "micGainValue");
    micGainValue=75;

However, the setting of micGainValue does not set micVolume in the flash file. I instead tried setting micGainValue after 200 frames, and it now does set micVolume. Is there a way to test that these properties are bound and so set the value after?

EDIT:

The flash file was actually changing the value. Now the question is, why does setting micVolume not change micGainValue.

This the c开发者_运维问答ode from my loaded flash file:

[Bindable]

    public function get micVolume():Number{
        if(microphone!=null)
            return microphone.gain;
        return 0;
    }

    public function set micVolume(val:Number):void{
        if(microphone!=null)
            microphone.gain=val;
    }

Flex databinding is implemented using events. When you use BindingUtils.bindProperty, what is happening behind the scenes is that an event listener is being added to the target object to listen for an event of type PropertyChangeEvent

If the target object does not dispatch the PropertyChangeEvent when it is changed, then binding will never be triggered.

When you add the [Bindable] attribute to properties in Flex, what you are doing is telling the framework to dispatch the PropertyChangeEvent when that property is changed. If you don't include the attribute (or put it on the class) then the event is not dispatched and binding doesn't happen.

That's why your binding is working from Flex to Flash but not the other way around- The Flex object is dispatching the required event when it is changed but the flash object is not.

Here is the info on PropertyChangeEvent

Personally, for Flash -> Flex I would dispatch my own event when the flash part changes its values and use a handler on that to update a bindable object within the Flex part. You can then bind other Flex stuff to that.