What is difference between MXML and ActionScript?
When you learn Flex there is often confusion between what MXML is and how it relates to ActionScript. We tend to think of it as different entities, but the reality is MXML is just an abstracted form of ActionScript. MXML is a declarative XML syntax that is converted by the compiler into an ActionScript class. This is an important concept to understand because this is the root of why the compiler throws an error when trying to have a MXML file and an ActionScript File with the same name in the same package. The MXML file is really just an ActionScript class and therefore we have a conflicting namespace error.
To help visualize this, imagine the root node of the MXML file is the same as an extends statement. When we use
something like this in MyFirstApp.mxml:
<mx:Application xmlns:mx="http://www.adobe.com/2006/mxml"> ... </mx:Application>
Means we are saying:
ublic class MyFirstApp extends Application
So why do we need MXML syntax if it just becomes ActionScript. As you are probably well aware, doing complex layout in ActionScript takes a ton of code, especially when you get into the world of nested layout. It can be done in code but why would you want to? XML is all about parent/child hierarchies and by using this as a layout language you can quickly define complex organizational structures that would have taken hundreds of lines of code if you did it all in ActionScript.