The first two chapters of this book introduced you to the Flex 2 product line and the concepts of Rich Internet Applications (RIA). This chapter explains how to build a Flex 2 application using the Application Model. First, before you build anything, you are introduced to the XML markup language (MXML) and ActionScript.
The following section, “Flex 2 Programming Model,” explains what the different elements are when developing your applications. The elements described are MXML, ActionScript, and the Flex 2 Framework.
Flex 2 Programming Model
The Flex 2 Programming Model consists of MXML, ActionScript, and the Flex class library. To build a full-fledged application, you must have a good knowledge of all these technologies. To start off, you are introduced to the basics of MXML. Then you are shown how ActionScript and MXML work together to create powerful, rich user interfaces.
The third element of the programming model is the Flex 2 Framework, which contains Flex components, managers, and behaviors. This component-based development model allows developers to incorporate pre-built components, extend the component library by creating new components, or combine pre-built components to create composite components.
MXML
The first element of the programming model, MXML, is an XML language that defines the user interface for an application. MXML is also used to define non-visual aspects such as server-side data sources and bindings between the user interface and the server side.
To write a Flex application, you must be able to write MXML and ActionScript. As mentioned earlier, MXML is an XML language that is used to lay out your user interface.
MXML is very similar to HTML in that it provides tags for user interface elements. If you have worked with HTML, then MXML should be very familiar to you. MXML has a much broader tag set than HTML, and defines visual components such as data grids, buttons, combo boxes, trees, tab navigators, and menus, as well as non-visual components, Web service connections, data binding, and effects.
The biggest difference between HTML and MXML is the MXML-defined file that is compiled into a Shockwave file (SWF) and rendered by the Flash Player. MXML can be written in a single file or in multiple files. MXML requires that you close off every tag that you declare in your Flex application. Otherwise, the Flex compiler will throw an error.
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