Watching a bindable property

Question

In my flex app I have a public bindable property. I want it so that every time the value of that property changes, a function gets triggered. I tried using ChangeWatchers, but it seems those only apply to built-in components like a text box change. I would like to do that same behavior with a property that changes at runtime.

Answer 1

One option is to use BindingUtils.bindSetter (which incidentally returns a ChangeWatcher):

<?xml version="1.0" encoding="utf-8"?>
<mx:Application xmlns:mx="http://www.adobe.com/2006/mxml" layout="absolute" creationComplete="this_creationComplete()">

    <mx:Script>
        <![CDATA[

            import mx.binding.utils.BindingUtils;
            import mx.binding.utils.ChangeWatcher;

            [Bindable]
            public var myValue:int = 0;

            private function this_creationComplete():void
            {
                var cw:ChangeWatcher = BindingUtils.bindSetter(myValueChanged, this, "myValue");
            }

            private function setValue():void
            {
                myValue = getTimer();
            }

            private function myValueChanged(o:Object):void
            {
                trace("myValue: " + myValue.toString());

                // You can also use o.toString() -- the new value will be passed into the function
            }

        ]]>
    </mx:Script>


    <mx:Button label="Click Me" click="setValue()" />

</mx:Application>

Here, myValueChanged gets called whenever the myValue property changes. There are other ways, of course, but I often use this approach with good results. Hope it helps! Post back with questions and I'll keep an eye out.