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One of the most noticeable improvements to error handling in
ActionScript 3.0 is the support for error event handling for responding
to asynchronous errors while an application is running. (For a definition
of asynchronous errors, see
Types of errors
.)
You can create event listeners and event handlers to respond
to the error events. Many classes dispatch error events the same
way they dispatch other events. For example, an instance of the
XMLSocket class normally dispatches three types of events:
Event.CLOSE
,
Event.CONNECT
,
and
DataEvent.DATA
. However, when a problem occurs,
the XMLSocket class can dispatch the
IOErrorEvent.IOError
or
the
SecurityErrorEvent.SECURITY_ERROR
. For more
information about event listeners and event handlers, see
Handling events
.
Error
events fit into one of two categories:
-
Error events that extend the ErrorEvent class
The
flash.events.ErrorEvent class contains the properties and methods
for managing errors related to networking and communication operations
in a running application. The AsyncErrorEvent, IOErrorEvent, and
SecurityErrorEvent classes extend the ErrorEvent class. If you’re
using the debugger version of a Flash runtime, a dialog box informs
you at run-time of any error events without listener functions that
the player encounters.
-
Status-based error events
The status-based error events
are related to the
netStatus
and
status
properties
of the networking and communication classes. If a Flash runtime encounters
a problem when reading or writing data, the value of the
netStatus.info.level
or
status.level
properties
(depending on the class object you’re using) is set to the value
"error"
.
You respond to this error by checking if the
level
property
contains the value
"error"
in your event handler
function.
Working with error events
The ErrorEvent
class and its subclasses contain error types for handling errors dispatched
by Flash runtimes as they try to read or write data.
The following example uses both a
try..catch
statement
and error event handlers to display any errors detected while trying
to read a local file. You can add more sophisticated handling code
to provide a user with options or otherwise handle the error automatically
in the places indicated by the comment “your error-handling code
here”:
package
{
import flash.display.Sprite;
import flash.errors.IOError;
import flash.events.IOErrorEvent;
import flash.events.TextEvent;
import flash.media.Sound;
import flash.media.SoundChannel;
import flash.net.URLRequest;
import flash.text.TextField;
import flash.text.TextFieldAutoSize;
public class LinkEventExample extends Sprite
{
private var myMP3:Sound;
public function LinkEventExample()
{
myMP3 = new Sound();
var list:TextField = new TextField();
list.autoSize = TextFieldAutoSize.LEFT;
list.multiline = true;
list.htmlText = "<a href=\"event:track1.mp3\">Track 1</a><br>";
list.htmlText += "<a href=\"event:track2.mp3\">Track 2</a><br>";
addEventListener(TextEvent.LINK, linkHandler);
addChild(list);
}
private function playMP3(mp3:String):void
{
try
{
myMP3.load(new URLRequest(mp3));
myMP3.play();
}
catch (err:Error)
{
trace(err.message);
// your error-handling code here
}
myMP3.addEventListener(IOErrorEvent.IO_ERROR, errorHandler);
}
private function linkHandler(linkEvent:TextEvent):void
{
playMP3(linkEvent.text);
// your error-handling code here
}
private function errorHandler(errorEvent:IOErrorEvent):void
{
trace(errorEvent.text);
// your error-handling code here
}
}
}
Working with status change events
Flash runtimes dynamically change
the value of the
netStatus.info.level
or
status.level
properties
for the classes that support the
level
property while
an application is running. The classes that have the
netStatus.info.level
property
are NetConnection, NetStream, and SharedObject. The classes that
have the
status.level
property are HTTPStatusEvent,
Camera, Microphone, and LocalConnection. You can write a handler function
to respond to the change in
level
value and track
communication errors.
The following example uses a
netStatusHandler()
function
to test the value of the
level
property. If the
level
property
indicates that an error has been encountered, the code traces the
message “Video stream failed”.
package
{
import flash.display.Sprite;
import flash.events.NetStatusEvent;
import flash.events.SecurityErrorEvent;
import flash.media.Video;
import flash.net.NetConnection;
import flash.net.NetStream;
public class VideoExample extends Sprite
{
private var videoUrl:String = "Video.flv";
private var connection:NetConnection;
private var stream:NetStream;
public function VideoExample()
{
connection = new NetConnection();
connection.addEventListener(NetStatusEvent.NET_STATUS, netStatusHandler);
connection.addEventListener(SecurityErrorEvent.SECURITY_ERROR, securityErrorHandler);
connection.connect(null);
}
private function netStatusHandler(event:NetStatusEvent):void
{
if (event.info.level == "error")
{
trace("Video stream failed")
}
else
{
connectStream();
}
}
private function securityErrorHandler(event:SecurityErrorEvent):void
{
trace("securityErrorHandler: " + event);
}
private function connectStream():void
{
var stream:NetStream = new NetStream(connection);
var video:Video = new Video();
video.attachNetStream(stream);
stream.play(videoUrl);
addChild(video);
}
}
}
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