Where is as2 _root in as3?

If you remember in as2 we had _root which let us access to methods and variables in the root of the project and refer to absolute paths, I thought that as3 didn’t have _root propriety, but I was wrong. root property can be useful if you want to share some value to all the classes in the project, add events to main class that call methods declared inside the class where we are working on or call generic methods declare in root class.

To use root propriety the class that you are working on most extend a DisplayObject (Sprite,MovieCLip,etc…) because you have to add the class to the parent class. And note, you can’t use the root propriety in the constructor method, because the addChild haven’t been process yet! Well let’s stop writing and see some code:

Main.as

In the Main class I’m declaring a variable named myValue which I did the proper sets and get. I am declaring two classes, in one of them I will set the value at the Main class and in the other I will get that value back. I’m also creating a movieClip just for test purposes.

ExampleClass.as

In ExampleClass I’m setting myValue that is propriety of the Main class with some text and I’m tracing the movieClip that I create in the Main Class.

AnotherClass.as

In AnotherClass I’m tracing the myValue propriety. So the result should be:
[object MovieClip]
This value is inside the Main Class

So it works ok, you only have to be carefull not refer root inside the constructor method, have the certain that you already addChild the class when you are referring to root and that the class extends a display object. If you do that, you can too have access to stage propriety, let’s check the next example:

ExampleClass.as

The result should be or stage width.

Another way to access to main proprieties, methods, etc… is with static members. In the next example I’m declaring a static property in the main class and setting and trace the value of it in the example class.

Main.as

ExampleClass.as

The result should be “Hello Word!”, if you didn’t know this, read some books about object oriented programming and static members.

Another way to do the same thing is to pass the instance of main class as an argument to the other classes.

Main.as

Example.as

There are still another ways to access to the Main class code. I don’t know which techniques are more correct, I usually use them all depending in what I need. I hope I help someone.

Flex Bindings in AS3 Projects

Since 99.9% of the work we do is Flash, we pretty much use flex builder to develop Actionscript Projects. One of the things I really wanted to have was bindings. Here's how to use Flex Bindings in Actionscript only projects.

Remember that the Flash framework (textfields, movieclips, sprites, etc) doesn't dispatch the data-binding event. This means that pretty much the only things you can bind are variables.

Make sure you add the flex framework.swc to your project Library Path to have access to the mx.binding.util class.

ChangeWatcher:

Acts like the watch on AS2. It watches a variable for changes and when something happens fires an event. Make sure you call the canWatch to ensure that you can watch it!

There are 3 ways to specify the second parameter, the chain.

1. A String containing the name of a public bindable property of the host object.

   ChangeWatcher.watch(this, "myvar", handler)

2. An Object in the form: { name: property name, access: function(host) { return host[name] } }. The Object contains the name of a public bindable property, and a function which serves as a getter for that property.

   ChangeWatcher.watch(this, { name:"myvar", getter: function():String { return "something" }}, handler);

3. A non-empty Array containing any combination of the first two options. This represents a chain of bindable properties accessible from the host. For example, to watch the property host.a.b.c, call the method as: watch(host, ["a","b","c"]

BindingUtils.bindProperty

Works pretty much the same way as the watch, but instead of having to handle and event it allows you to immediately bind two properties one-way.
The first two parameters are for the the target, the second parameters are the triggers.

BindingUtils.bindProperty( this, "va1", this, "var2");

you can also use the same syntax for the chain.

References: