Kevin escreveu:
>>
>> 1st; when i use function biding (<textInput
>> text="{myInstance.toString()}"/>) , function binding works fine
>>
> are you sure about that? I could be wrong, but I would guess that if
> you add a button under the TextInput tag your TextInput text value
> will not update as expected on the button click.
>
> <mx:Button label="Test" click="myInstance.someProperty = 'testing';" />
>
> (If in fact it does update for you, I would love to see your example
> code since it's possible there is an aspect of binding that I am missing.)
>
> HOWEVER, the problem you are having with the item renderer is somewhat
> related, but different, problem. Item renderers use 'data' as
> generic object to hold the data passed to the item render. That
> object itself is bindable AND if the entire data object changes the
> functions and properties will update. However, changes to the
> underlying properties or functions will not be detected without
> setting up binding a little more explicitly. (Usually you don't get
> compiler warnings, but it you run in debug mode you should get run
> time messages in the console) My solution to this is to explicitly
> bind the data property to an internal property of the item renderer
> using MXML. When I do this the binding works correctly.
>
> In my item renderer...
>
> <mx:Script>
> <![CDATA[
> [Bindable]
> private var myInternalData:MyCustomClass;
> ]]>
> </mx:Script>
> <mx:Binding source="(data as MyCustomClass)" source="myInternalData" />
> <mx:Label text="{myInternalData.myFunction()}" />
>
> Hopefully that helps your item renderer problem.
>
> You are correct. Functions can be "bound" BUT I think what Frederico
> was pointing out is that there are some important things to understand
> when binding with functions (which are stated in the document that you
> referenced.) It is not as easy as just putting the function in curly
> braces.
>
> "You can use ActionScript functions as the source of data binding
> expressions *when using a bindable property** as an argument* of the
> function. "
>
> If you do not pass a parameter to the function then flex has no way of
> knowing when to update the function. You can do a quick test of this
> by running this test:
>
> <?xml version="1.0" encoding="utf-8"?>
> <mx:Application xmlns:mx="http://www.adobe.com/2006/mxml";
> layout="vertical" horizontalAlign="center">
> <mx:Script>
> <![CDATA[
>
>
> [Bindable]
> public var myData:String = 'old data';
>
>
> private function myFunction(data:String = null):String{
> return myData;
> }
>
>
> ]]>
> </mx:Script>
> <mx:Label text="{myData}" />
> <mx:Label text="{myFunction(myData)}" />
> <mx:Label text="{myFunction()}" />
> <mx:Button label="Test" click="myData = 'new data';" />
> </mx:Application>
>
> as you can see the first two labels will update correctly because they
> have a reference to some underlying data. When that data changes Flex
> knows to execute the function again. The other option (as you pasted
> in your last email) is to dispatch an event from a setter so that flex
> will know to update the function that relies on the set data:
>
> <?xml version="1.0" encoding="utf-8"?>
> <mx:Application xmlns:mx="http://www.adobe.com/2006/mxml";
> layout="vertical" horizontalAlign="center">
> <mx:Script>
> <![CDATA[
>
>
> private var _myData:String = 'old data';
>
>
> public function set myData(value:String):void{
> _myData = value;
> dispatchEvent(new Event("myDataChanged"));
> }
>
>
> [Bindable]
> public function get myData():String{
> return _myData;
> }
>
> [Bindable(event="myDataChanged")]
> private function myFunction(data:String = null):String{
> return _myData;
> }
>
>
> ]]>
> </mx:Script>
> <mx:Label text="{myData}" />
> <mx:Label text="{myFunction(myData)}" />
> <mx:Label text="{myFunction()}" />
> <mx:Button label="Test" click="myData = 'new data';" />
> </mx:Application>
>
> As you can see all the labels now update properly.
>
> - Kevin
>
>
>
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Thanks Kevin,
Great post on function binding.
I believe function binding is quite cool, BUT troublesome and needless.
Binding a property to a function with no parameters is the same as
binding to a getter. Most Binding issues can be solved using the
solution I first provided.
Regards,
Frederico Garcia
