Before we start creating actual “HelloWorld” application using Flash Builder, let us see what the actual parts of a Flex application are −

A Flex application consists of the following four important parts, out of which last part is optional but first three parts are mandatory.

• Flex Framework Libraries
• Client-side code
• Public Resources (HTML/JS/CSS)
• Server-side code

Sample locations of different parts of a typical Flex application like HelloWord will be as shown below −

Application Build Process

To start with, Flex application requires Flex framework libraries. Later, Flash Builder automatically adds the libraries to build path.

When we build our code using Flash builder, Flash builder will do the following tasks −

• Compiles the source code to HelloWorld.swf file.

• Compiles a HelloWorld.html (a wrapper file for swf file) from a file index.template.html stored in html-template folder

• Copies HelloWorld.swf and HelloWorld.html files in target folder, bin-debug.

• Copies swfobject.js, a JavaScript code responsible to load swf file dynamically in HelloWorld.html in target folder, bin-debug

• Copies framework libraries in form of swf file named frameworks_xxx.swf in target folder, bin-debug

• Copies other flex modules (.swf files such as sparkskins_xxx.swf, textLayout_xxx.swf) in target folder.

Application Launch Process

• Open the HelloWorld.html file available in HelloWorldbin-debug folder in any web-browser.

• HelloWorld.swf will load automatically and application will start running.

Flex Framework Libraries

Following is the brief detail about few important framework libraries. Please note that, Flex libraries are denoted using .swc notation

Client-side Code

Flex application code can be written in MXML as well as ActionScript.

In Flex, we can mix ActionScript and MXML, to do the following −

• Layout user interface components using MXML tags

• Use MXML to declaratively define nonvisual aspects of an application, such as access to data sources on the server

• Use MXML to create data bindings between user interface components and data sources on the server.

• Use ActionScript to define event listeners inside MXML event attributes.

• Add script blocks using the

• Include external ActionScript files.

• Import ActionScript classes.

• Create ActionScript components.

Public Resources

These are help files referenced by Flex application, such as Host HTML page, CSS or images located under html-template folder. It contains following files −

HelloWorld.mxml

This is the actual MXML/AS (ActionScript) code written implementing the business logic of the application and that the Flex compiler translates into SWF file which will be executed by flash player in the browser.

A sample HelloWorld Entry class will be as follows −

<?xml version = "1.0" encoding = "utf-8"?>
<s:Application xmlns:fx = "http://ns.adobe.com/mxml/2009" 
   xmlns:s = "library://ns.adobe.com/flex/spark" 
   xmlns:mx = "library://ns.adobe.com/flex/mx"
   width = "100%" height = "100%"
   minWidth = "500" minHeight = "500" 
   initialize = "application_initializeHandler(event)">

   <fx:Script>
      <![CDATA[
         import mx.controls.Alert;
         import mx.events.FlexEvent;
         protected function btnClickMe_clickHandler(event:MouseEvent):void {
            Alert.show("Hello World!");				
         }

         protected function application_initializeHandler(event:FlexEvent):void {
            lblHeader.text = "My Hello World Application";				
         }
      ]]>
   </fx:Script>
   
   <s:VGroup horizontalAlign = "center" width = "100%" height = "100%" 
      paddingTop = "100" gap = "50">
      <s:Label id = "lblHeader" fontSize = "40" color = "0x777777" />
      <s:Button label = "Click Me!" id = "btnClickMe" 
         click = "btnClickMe_clickHandler(event)" />
   </s:VGroup>	
</s:Application>

Following table gives the description of all the tags used in the above code script.

Server-side code

This is the server side part of your application and it’s very much optional. If you are not doing any backend processing within your application, then you do not need this part but if there is some processing required at backend and your clientside application interacts with the server, then you will have to develop these components.

In the next chapter, we will use all the above-mentioned concepts to create a HelloWorld application using Flash Builder.