Full code after the jump.

The following example(s) require Flash Player 10 and the Adobe Flex 4 SDK. To download the Adobe Flash Builder 4 trial, see http://www.adobe.com/products/flex/. To download the latest nightly build of the Flex 4 SDK, see http://opensource.adobe.com/wiki/display/flexsdk/Download+Flex+4.
For more information on getting started with Flex 4 and Flash Builder 4, see the official Adobe Flex Team blog.

View MXML

<?xml version="1.0" encoding="utf-8"?>
<!-- http://blog.flexexamples.com/2009/07/14/using-the-halo-theme-in-flex-4/ -->
<s:Application name="Spark_Halo_theme_test"
        xmlns:fx="http://ns.adobe.com/mxml/2009"
        xmlns:s="library://ns.adobe.com/flex/spark"
        xmlns:mx="library://ns.adobe.com/flex/halo">
 
    <s:VGroup horizontalCenter="0" verticalCenter="0" >
        <s:Button id="sBtn"
                label="I'm a Spark Button" />
 
        <mx:Button id="hBtn"
                label="I'm a Halo Button" />
    </s:VGroup>
 
</s:Application>

Finally, you need to change your Flex compiler arguments to use the halo.swc theme:
1) In Flash Builder 4, select Project > Properties from the main menu.
2) Select Flex Compiler from the left menu.
3) In the Additional compiler arguments text field, add the following argument:

-theme=${flexlib}/themes/Halo/halo.swc

4) Click the OK button to apply the changes and close the dialog box.
5) Recompile and run the application.

This entry is based on a beta version of the Flex 4 SDK and therefore is very likely to change as development of the Flex SDK continues. The API can (and will) change causing examples to possibly not compile in newer versions of the Flex 4 SDK.

 

Full code after the jump.

View MXML

<?xml version="1.0" encoding="utf-8"?>
<!-- http://blog.flexexamples.com/2008/12/21/using-a-custom-flex-configxml-file-in-flex-builder-3/ -->
<mx:Application name="LoadConfig_fonts_test"
        xmlns:mx="http://www.adobe.com/2006/mxml"
        layout="vertical"
        verticalAlign="middle"
        backgroundColor="white">

    <mx:Style>
        @font-face {
            src: url("assets/ARIAL.TTF");
            fontFamily: "ArialEmbedded";
            unicodeRange: "englishRange";
        }

        Text {
            fontFamily: "ArialEmbedded";
            fontSize: 32;
            color: red;
        }
    </mx:Style>

    <mx:ApplicationControlBar dock="true">
        <mx:Form styleName="plain">
            <mx:FormItem label="alpha:">
                <mx:HSlider id="slider"
                        minimum="0.0"
                        maximum="1.0"
                        value="1.0"
                        snapInterval="0.05"
                        tickInterval="0.1"
                        liveDragging="true" />
            </mx:FormItem>
        </mx:Form>
    </mx:ApplicationControlBar>

    <mx:Text id="txt" width="300" alpha="{slider.value}">
        <mx:text>The quick brown fox jumps over the lazy dog. 1234567890 ©</mx:text>
    </mx:Text>

</mx:Application>

Next, create a custom configuration XML file named fontConfig.xml and save it in a /config/ subdirectory in your project’s /src/ directory. The folder structure isn’t important, but it helps keep the source code and configuration files separated. The fontConfig.xml file is a modified version of the flex-config.xml file found in the Flex SDK’s /frameworks/ directory. In this example we simply specify a single named font range which specifies a unicode range of U+0020 (space) to U+007E (~).

config/fontConfig.xml

<?xml version="1.0"?>
<flex-config>
   <compiler>
      <fonts>
          <!-- Defines ranges that can be used across multiple font-face declarations. -->
          <!-- See flash-unicode-table.xml for more examples. -->
          <languages>
              <language-range>
                  <lang>englishRange</lang>
                  <range>U+0020-U+007E</range>
              </language-range>
          </languages>
      </fonts>
   </compiler>
</flex-config>

Finally, in Flex Builder, right click on the Flex Project folder in the Flex Navigator and select Properties from the context menu. Select the Flex Compiler section of the dialog menu and in the Additional compiler arguments: text box add the following text:

-load-config+=config/fontConfig.xml

Figure 1. Additional compiler arguments.

View source is enabled in the following example.