Xml – Duplicate complex MXML binding in ActionScript

apache-flexdata-bindingmxml

MXML lets you do some really quite powerful data binding such as:

<mx:Button id="myBtn" label="Buy an {itemName}" visible="{itemName!=null}"/>

I've found that the BindingUtils class can bind values to simple properties, but neither of the bindings above do this. Is it possible to do the same in AS3 code, or is Flex silently generating many lines of code from my MXML?
Can anyone duplicate the above in pure AS3, starting from:

var myBtn:Button = new Button();
myBtn.id="myBtn";
???

Best Answer

The way to do it is to use bindSetter. That is also how it is done behind the scenes when the MXML in your example is transformed to ActionScript before being compiled.

// assuming the itemName property is defined on this:
BindingUtils.bindSetter(itemNameChanged, this, ["itemName"]);

// ...

private function itemNameChanged( newValue : String ) : void {
  myBtn.label   = newValue;
  myBtn.visible = newValue != null;
}

...except that the code generated by the MXML to ActionScript conversion is longer as it has to be more general. In this example it would likely have generated two functions, one for each binding expression.

Related Solutions

Actionscript – flex 3 accessing main mxml from actionscript code

David is right -- while you can access the public members of your Application.mxml object statically and from anywhere in your application, design-wise that's a bit of a no-no. It's better to strive for loose coupling between your objects, and the way that's done in the Flex idiom is generally to extend EventDispatcher and to dispatch events. So for example, your WebService wrapper might look something like this:

public class MyWrapperClass extends EventDispatcher
{
    [Event(name="webserviceComplete", type="flash.events.Event")]

    public function MyWrapperClass(target:IEventDispatcher=null)
    {
        super(target);
    }

    private function handleWebServiceLoadComplete(event:ResultEvent):void
    {
        dispatchEvent(new Event("webserviceComplete"));
    }

    public function doWork():void
    {
        // Load the service, etc., and ultimately call handleWebServiceLoadComplete()...
    }       
}

... and your Main.mxml file like this:

<mx:Script>
    <![CDATA[

        private function app_creationComplete(event:Event):void
        {
            var myWrapper:MyWrapperClass = new MyWrapperClass();
            myWrapper.addEventListener("webserviceComplete", mywrapper_webServiceComplete, false, 0, true);
            myWrapper.doWork();
        }

        private function mywrapper_webServiceComplete(event:Event):void
        {
            // Do the work you would've otherwise done in the public method
        }

    ]]>
</mx:Script>

In this case, the end result is the same -- completing the web-service load triggers the function in Main.mxml. But notice how mywrapper_webServiceComplete() is declared privately -- it's not called directly by MyWrapperClass. Main.mxml simply subscribes (with addEventListener()) to be notified when MyWrapperClass is finished doing its work, and then does its own work; MyWrapperClass knows nothing about the details of Main.mxml's implementation, nor does Main.mxml know anything about MyWrapperClass other than that it dispatches a webserviceComplete event, and exposes a public doWork() method. Loose coupling and information hiding in action.

Good luck!

R – Flex: Binding to an MXML-esque “binding string” in action script

(Shameless plug)

BindageTools can do this:

Bind.fromProperty(this, "myArrayCollection", itemAt(0))
    .toProperty(this, "first_item");

Bind.fromAll(
    Bind.fromProperty(this, "somePerson.first"),
    Bind.fromProperty(this, "somePerson.last")
    )
    .format("Name: {0} {1}")
    .toProperty(this, "nameLbl.text");

Note that BindageTools puts the source object first and the destination last (whereas BindingUtils puts the destination first and the source last).

Best Answer

Related Solutions

Actionscript – flex 3 accessing main mxml from actionscript code

R – Flex: Binding to an MXML-esque “binding string” in action script

Related Topic