what are the advantages of using mxml over actionscript in a flex application?

Question

they both seem to accomplish the same things with different syntax, whats the point of using two different technologies. Please highlight every possible benefit of using mxml. Also are there scenarios when one is more beneficial than the other and why.

Please clarify this runtime behavior of mxml vs AS3 as discussed in Oreilly Flex 4 Cookbook page 1:

" Many newcomers to Flex wonder how MXML and ActionScript relate to one another. The MXML compiler (mxmlc), after parsing through the different idioms, translates them into the same objects, so that this:

<s:Button id="btn" label="My Button" height="100"/>

and this:

var btn:Button = new Button();
btn.label = "My Button";
btn.height = 100;

produce the same object. The major difference is that while creating that object in ActionScript (the second example) creates the button and nothing else, creating the object in MXML adds the button to whatever component contains the MXML code. The Flex Framework handles calling the constructor of the object described in MXML and either adding it to the parent or setting it as a property of the parent. "

Answer 1

Usually,

• MXML is used to build the user interface
• ActionScript is used to code the logic of your application

Of course, you can also build the user interface with ActionScript but :

• it will take you more time
• MXML views are easier to read than AS views

In terms of user interface, ActionScript should be used only to manage view elements (add, remove, ...) at runtime.

Answer 2

Edit

Within a Flex application, one is expected to favor using mxml over AS, provided both uses are available. In case mxml doesn't provide a solution , the user can fallback to AS3. Flex is a framework, therefore you would expect that the emphasis is put towards mxml, rather than AS3. Like most frameworks , the idea is to hide the details in order to facilitate design and supposedly make programming more accessible.

Everything comes at a cost though, you can't really expect mxml to be faster than AS3 since it's built on top of it. A logical conclusion would be to decide on a case basis. What are your app requirements, is there really a performance gain in using this component or not etc... Apart from the fact that Flex as a whole is bound to be slower than AS3, I don't think you can set general rules. One could add that if one is worried about performance, why choose Flex in the first place...

End of Edit

The Flex framework is geared towards building RIAs, therefore it comes with a bunch of components to that effect and mxml which mainly deals with the layout of these components, Actionscript being the language the Flex framework is built upon, will typically be used for the logic of your application.

The question is not really why choose one over the other. It's the same approach you would have if you decide to develop using a language directly or using a framework based on this language. It's like comparing JQuery & Javascript or CodeIgniter & PHP .I don't mean to imply that the reasons to use JQuery are the same regarding using Flex. Whilst JQuery will attempt to hide browser specificities and make JS more accessible , Flex's purpose is entirely different.

If you're developing RIAs, Flex makes sense, if you're developing games, not really. All you can do with Flex can be done with AS3 , only you wouldn't want to spend time developing DataGrids or HBoxes whilst you could spend more time on your app structure & design.

On the other hand, if you're developing a website or a game , you wouldn't want to add the weight of the Flex framework to your swf, simply because you've added a few Image components and a couple of Labels.

Flex is not adapted to every situation, unlike my previous Javascript or Php examples , Flex's purpose is not to make the language it's based upon more accessible or easier to deal with. Flex has a very specific target.