Macromedia flex 2-migrating applications to flex 2 Manual De Usuario

Using mixins

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Using mixins

You can no longer attach a function to a class, unless that class has prior knowledge of that 
function. For example, you can no longer do this:

UIComponent.prototype.doSomething = myFunction

or this:

dataGridInstance.doSomething = myFunction

You can still declare a Function type property on an Object and then supply an 
implementation of that function later. For example:

class MyButton extends Button {

var doSomething:Function;
public function processInput(condition:Boolean):void {
if (condition)

doSomething();

}

}

and then:

var b:MyButton = new MyButton();
b.doSomething = function () { ... };
b.processInput(true);

You can also apply mixins to dynamic classes without their prior knowledge, as the following 
example shows:

dynamic class MyButton extends Button {

...

}

and then:

// You can mix in any function onto an instance of a dynamic class:
var b:MyButton = new MyButton();
b.anyFunctionNameYouCanImagine = function () { ... };

// After it's added, you can call the function as follows:
b.anyFunctionNameYouCanImagine();

The only class in the Flex class library that is dynamic is the Object class. In most cases, you 
must create your own class.