Introduction to ActionScript 3 & MXML

One interesting question arose while we were looking at the dynamic class modifier:

“Is there a typical case where I need to use the dynamic keyword?”

And while I was trying to answer this question, we end up discussing Type-safe vs. Dynamic programming languages.
The thing is that I’m still unable to find a case where we can’t live without dynamic classes. The dynamic keyword simply adds some dynamic programming capabilities into ActionScript 3.0. Such capabilities where quite common to ActionScript 2.0, but since ActionScript 3.0 is trying to solve a lot of performance issues the dynamism of the language was changed with a type-safety. But still the Object, the MovieClip, the TextField and others are kept dynamic.

You won’t regret if you check this really cool article on dynamic classes:
ActionScript 3: Dynamic classes
And another fun article in the same blog, but somewhat related to the topic above:
Adobe Flex: Program in Style or an Elevator Pitch

Having the capability to do stuff typical for the dynamic programming languages brings the questions:

“How am I supposed to exploit the productivity of the dynamic languages without making a complete mess?”

I believe a nice discussion about this you can find in the Bruce Eckel’s article Strong Typing vs. Strong Testing.

I’ve tested the [ArrayElementType] metadata tag and I can conclude that it does almost nothing – no compile warnings, no run-time warnings or errors, no nothing… It seem so… but there is one case where it works. It works only in conjunction with [DefaultProperty] metadata tag:

TestArrayElementType.as

package test
{
    [DefaultProperty("array")]
    public class TestArrayElementType
    {
        [ArrayElementType("test.SomeType")]
        public var array : Array = new Array();
    }
}

app.mxml

<?xml version="1.0" encoding="utf-8"?>
<mx:Application layout="absolute"
    xmlns:mx="http://www.adobe.com/2006/mxml" xmlns:test="test.*">

    <test:TestArrayElementType>
        <!-- Here when we are adding array elements the Flex Builder code hinting will suggest us <test:SomeType... -->
        <test:SomeType/>
        <test:SomeType/>
        <test:AnotherType/>     <!-- This line will give a compile error  -->
    </test:TestArrayElementType>

    <test:TestArrayElementType>
        <test:array>
            <mx:Array>
                <test:SomeType/>
                <test:SomeType/>
                <test:AnotherType/> <!-- This line WILL NOT give a compile error (Go Figure)  -->
            <mx:Array/>
        <test:array/>
    </test:TestArrayElementType>

</mx:Application>

Anyway it looks like the [ArrayElementType] metadata tag is poorly designed and very poorly documented.

The first Lab will start with some quick hands-on using ActionScript 3 with the following goals in mind:
1. Referencing AS3 library projects.
2. Understanding AS3 Reflection:
– getQualifiedClassName() (check documentation);
– getQualifiedSuperclassName() (check documentation);
– ApplicationDomain.currentDomain.getDefinition() (check documentation);
– describeType() (check documentation);
3. Hands-on experience with XML, E4X, and various AS3 constructs.
4. Compiling custom metadata tags.

The exercise projects are incomplete samples, in which you’ll need to fill in the missing functionallity:
DOWNLOAD EXERCISE AS3 LIBRARY PROJECT
DOWNLOAD EXERCISE FLEX PROJECT

If you want to see the completed projects:
DOWNLOAD COMPLETED AS3 LIBRARY PROJECT
DOWNLOAD COMPLETED FLEX PROJECT

Group 6 Training Exercise 1:

DOWNLOAD LAB 01 LIBRARY PROJECT
DOWNLOAD LAB 01 PROJECT