Recipe 2.8. Dispatching Events

Problem

You want to dispatch events.

Solution

Extend flash.events.EventDispatcher and call the dispatchEvent( ) method.

Discussion

Events are an important way for objects to communicate. They are essential for creating flexible systems. Flash Player 9, for example, has a built-in event dispatching mechanism in the flash.events.EventDispatcher class. All classes that dispatch events inherit from EventDispatcher (e.g., NetStream and Sprite ). If you want to define a class that dispatches events, you can extend EventDispatcher , as follows :

package {
    import flash.events.EventDispatcher;
    public class Example extends EventDispatcher {

    }
}

The EventDispatcher class has public methods called addEventListener( ) and removeEventListener( ) that you can call from any instance of an EventDispatcher subclass to register event listeners. EventDispatcher also defines a protected method called dispatchEvent( ) , which you can call from within a subclass to dispatch an event. The dispatchEvent( ) method requires at least one parameter as a flash.events.Event object or a subclass of Event .

Chapter 3. Runtime Environment

Section 3.0. Introduction

Recipe 3.1. Detecting the Player Version

Recipe 3.2. Detecting the Operating System

Recipe 3.3. Checking the Player Type

Recipe 3.4. Checking the System Language

Recipe 3.5. Detecting Display Settings

Recipe 3.6. Scaling the Movie

Recipe 3.7. Changing the Alignment

Recipe 3.8. Hiding the Flash Player's Menu Items

Recipe 3.9. Detecting the Device's Audio Capabilities

Recipe 3.10. Detecting the Device's Video Capabilities

Recipe 3.11. Prompting the User to Change Player Settings

Recipe 3.12. Dealing with System Security

3.0. Introduction

Flash Player 9 offers a relatively large amount of information about and control over the runtime environment. The flash.system.Capabilities class has many static methods that return information about the player and the computer on which it is running, such as the operating system, language, audio, and video capabilities. There are other classes such as flash.display.Stage and flash.system.Security that allow you to control other elements of the Player such as the right-click menu under Windows (Control-click on the Macintosh) and the Settings dialog box. The flash.display.Stage class also controls the scaling and alignment of the movie within the Player.

Perhaps one of the most significant updates to Flash Player 7 within this chapter's subject matter is the ability to work with the context menu with more detail and precision than was allowed in previous versions of the player. In Flash Player 7, using the ContextMenu class, you can programmatically remove items from the context menu, and perhaps more importantly, you can add items to the menu. And as the name suggests, you can make the context menu so it is actually contextual, so that items in the menu are based on the object on which the menu is being displayed.

Recipe 3.1. Detecting the Player Version

Problem

You want to ensure that the user has the correct version of the Flash Player.

Solution

Use the Flash Player Detection Kit, available on Adobe's web site to check the version of player and, if necessary, initiate a player upgrade (http://www.adobe.com/software/flashplayer/download/detection_kit).

Discussion

Detecting the currently installed version of the Flash Player in the user's browser has been a problem for years , and there have been many solutions used by various developers. They generally fall into three categories:

Browser-based script detection
Server-side detection
ActionScript detection

The first method uses JavaScript or VBScript to detect the version of the Flash Player the user has installed. Many of these scripts were prone to errors due to differences in platforms and browser types.

Server-side detection can be difficult if you don't have the ability to create server-side scripts.

Most ActionScript-based player detection techniques won't work directly in an ActionScript 3.0-based .swf . While ActionScript 1.0 and 2.0 had various object methods , variables , and functions that would return the player version, none of those are now valid in an ActionScript 3.0 class. ActionScript 3.0 has its own way of detecting the player versionthe flash.system.Capabilities.version property. This, of course, won't work at all with any version of the Flash Player prior to 8.5, so it is rather useless for Flash detection.

Adobe has researched all of these issues thoroughly, and came out with a Flash Player Detection Kit that guides you through the recommended procedures for best detecting the player version.

The kit includes documentation on the various issues and potential solutions, including sample VBScript and JavaScript for browser-based detection; .flas , .as , and .swf files for ActionScript detection; as well as ColdFusion and PHP scripts for server-side detection.

ActionScript-based detection works successfully as long as the user has any version of the Flash Player from Version 4 on up. Basically, it is a Flash 4 .swf that executes a script to detect the current player version; all you need to do is set your minimum content version as a variable in the script. If the player version is at least as high as the content version, it loads the specified content. If not, it redirects the browser to an alternate content page. This page can contain a lower version .swf , a non-Flash version of the content, or a notice instructing the user to upgrade his Flash Player, with a link to the player install page on Adobe's site.

Furthermore, the kit contains a .swf and HTML template that initializes an Express Install of the latest version of the Flash Player. If the user's player is not adequate, the browser is redirected to this .swf , which downloads the latest version of the Flash Player from Adobe's site, automatically installs it, and finally redirects the user back to the specified Flash content, all without the user ever leaving your site. This option requires that the user already have Version 6.0.65.0 of the Flash Player installed.

Using a combination of the techniques included in the Flash Player Detection Kit gives you very precise control over the Flash Player version and the content you deliver to your viewers .

For testing purposes, older versions of the Flash Player can be obtained from Macromedia's site (http://www.adobe.com/cfusion/knowledgebase/index.cfm?id=tn_14266).

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Lott J., Schall D., Peters K.

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