ACTIONSCRIPT 3 Developer’s Guide en

ACTIONSCRIPT 3.0 DEVELOPER’S GUIDE
Handling errors
var fileRef:FileReference = new FileReference();
fileRef.addEventListener(Event.SELECT, selectHandler);
fileRef.addEventListener(Event.OPEN, openHandler);
fileRef.addEventListener(Event.COMPLETE, completeHandler);
fileRef.browse();
function selectHandler(event:Event):void
{
trace("...select...");
var request:URLRequest = new URLRequest("http://www.yourdomain.com/fileupload.cfm");
request.method = URLRequestMethod.POST;
event.target.upload(request);
}
function openHandler(event:Event):void
{
trace("...open...");
}
function completeHandler(event:Event):void
{
trace("...complete...");
}
For detailed information on asynchronous error handling, see “Responding to error events and status” on page 63.
Uncaught exceptions are errors thrown with no corresponding logic (like a catch statement) to respond to them.
If your application throws an error, and no appropriate catch statement or event handler can be found at the
current or higher level to handle the error, the error is considered an uncaught exception.
When an uncaught error happens, the runtime dispatches an uncaughtError event. This event is also known as a
“global error handler.” This event is dispatched by the SWF’s UncaughtErrorEvents object, which is available
through the LoaderInfo.uncaughtErrorEvents property. If no listeners are registered for the uncaughtError
event, the runtime ignores uncaught errors and tries to continue running, as long as the error doesn’t stop the SWF.
In addition to dispatching the uncaughtError event, debugger versions of the Flash runtime respond to uncaught
errors by terminating the current script. Then, they display the uncaught error in trace statement output or
writing the error message to a log file. If the exception object is an instance of the Error class or one of its subclasses,
the getStackTrace() method is called. The stack trace information is also displayed in trace statement output or
in a log file. For more information about using the debugger version of Flash runtimes, see “Working with the
debugger versions of Flash runtimes” on page 57.
Note: While processing an uncaughtError event, if an error event is thrown from an uncaughtError handler, the event
handler is called multiple times. This results in an infinite loop of exceptions. It is recommended that you avoid such
a scenario.
Error handling in ActionScript 3.0
Flash Player 9 and later, Adobe AIR 1.0 and later
Since many applications can run without building the logic to handle errors, developers are tempted to postpone
building error handling into their applications. However, without error handling, an application can easily stall or
frustrate the user if something doesn’t work as expected. ActionScript 2.0 has an Error class that allows you to build
logic into custom functions to throw an exception with a specific message. Because error handling is critical for making
a user-friendly application, ActionScript 3.0 includes an expanded architecture for catching errors.
Last updated 6/6/2012
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