On occasion you may want to create classes dynamically by name. To do this in Flex 3 you can use getDefinitionByName (it's previous incarnation was getClassByName). Here's a quick example:

The docs for getDefinitionByName say:

"Returns a reference to the class object of the class specified by the name parameter."

...so you may be wondering why in the above code we needed to specify the return value as a Class? This is because getDefinitionByName can also return a Function (e.g. 'flash.utils.getTimer' - a package level function that isn't in any class). As the return type can be either a Function or a Class the Flex team specified the return type to be Object and you are expected to perform a cast as necessary.

The above code closely mimics the example given in the docs, but in one way it is a bad example because everything will work fine for "flash.display.Sprite", but try to do the same thing with a custom class and you will probably end up with the following error:

ReferenceError: Error #1065: Variable [name of your class] is not defined.

The reason for the error is that you must have a reference to your class in your code - e.g. you need to create a variable and specify it's type like so:

Without doing this your class will not be compiled in to the .swf at compile time - and there is reason behind this madness. The compiler only includes classes which are actually used (and not just imported). It does so in order to optimise the size of the .swf. So the need to declare a variable should not really be considered an oversight or bug, although it does feel hackish to declare a variable that you don't directly use.

Here is the code your would need to create a custom class called Person from a string (where Person resides in the top level package along with your default application).

You can declare properties for all possible classes that you intend to create but if you are not happy with doing that inside your main app Alex Harui has another suggestion (something I've not personally tried yet):

"The code for the class has to be in a SWF. It can be in the main SWF or
loaded via a module later. There is a compiler option (-includes) that
allows you to stuff other classes into a SWF without explicitly naming
them in your source code."

Passing in Parameters

Another thing you may find yourself wanting to do is to pass parameters to the constructor of your class (indeed, this is what got me on to the subject today). As far as I'm aware this isn't possible to do this in AS3 (and isn't part of the ECMA spec so it is unlikely to change - please leave a comment or email if you know otherwise ), so you may want to set up another method which can accept and set multiple parameters . If you pass in an array you may stumble across another problem - the original array you passed in becomes the first item of a new array ... okay, that probably sounds confusing so see here for a similar example and solution. In short, the solution is to use Function.apply, and you can see how I used it below:

Now, I'm not sure if this is the best approach, but it works, and with a deadline approaching that's good enough for now :]

u dont have to create a variable, its enough just to reference to the class somewhere in the code;

package example
{
import example.items.*;
import flash.utils.getDefinitionByName;

// force import
example.items.Class1;
example.items.Class2;

class Test
{
public function Test()
{
var test:Class = getDefinitionByName(”example.items.Class1?) as Class;

var testInstance = new test();
}
}
}