ActionScript 3: Imports vs Includes

There are two different ways that you can use ActionScript 3 code inside a Flex Component or ActionScript class. One way is to use an import statement, the other way is to use an include. This topic came up recently on the FlexCoder's list where one person was trying to use include when he should have used an import. I thought I'd talk a bit about the difference.

The import directive is the one I I use most often. It allow you to make use of one ActionScript class from within another.

Let's pretend we have this simple ActionScript class:

I gave this class a single method named getFoo. It returns a string. I also made the method a static method, so for the purposes of this example we don't have to worry about creating an instance of a class.

We can import the class into the main application, like this

This code imports two classes; our custom one and the Alert class. The button will call the method and show the value. That is the simple example of an import.

When writing ActionScript, you'll find yourself using the import all the time, often importing the framework classes as well as your own to put together your application, just like the example above. Includes. Your include file should only contain a code snippet, not a class definition. Repeating our previous example. This is the include:

And it is included like this:

In this case, the include file is added as part of our main Application. In the first case, they are kept separate. Both offer valid reuse cases.

In the Flex Framework, an include is used to define the version numbers of the class. In my own development I once used an included to populate a state drop down. Since states don't change often, I Decided not to populate the drop down dynamically. I used a hard coded dataProvider. The 50+ lines of code needed to create the dataProvider was getting tedious to scroll back and forth through when editing the component. Removing that code from the main component and putting it in an include allowed to simplify those 50 lines of code into 1. The compiler places the include code back into the main component before turning it into binary goodness.

So, in summary, Imports are always performed on classes. Includes are always performed on independent code snippets. Each has their place in developing ActionScript code.