ACTIONSCRIPT 3 Developer’s Guide en

ACTIONSCRIPT 3.0 DEVELOPER’S GUIDE
Handling errors
Run-time errors occur when you run your application after you compile it. Run-time errors represent errors that
are caused while a SWF file plays in a Flash runtime (such as Adobe Flash Player or Adobe AIR). In most cases, you
handle run-time errors as they occur, reporting them to the user and taking steps to keep your application running.
If the error is a fatal error, such as not being able to connect to a remote website or load required data, you can use
error handling to allow your application to finish, gracefully.
Synchronous errors are run-time errors that occur at the time a function is called—for example, when you try to use
a specific method and the argument you pass to the method is invalid, so the Flash runtime throws an exception.
Most errors occur synchronously—at the time the statement executes—and the flow of control passes immediately
to the most applicable catch statement.
For example, the following code excerpt throws a run-time error because the browse() method is not called before
the program attempts to upload a file:
var fileRef:FileReference = new FileReference();
try
{
fileRef.upload(new URLRequest("http://www.yourdomain.com/fileupload.cfm"));
}
catch (error:IllegalOperationError)
{
trace(error);
// Error #2037: Functions called in incorrect sequence, or earlier
// call was unsuccessful.
}
In this case, a run-time error is thrown synchronously because Flash Player determined that the browse() method
was not called before the file upload was attempted.
For detailed information on synchronous error handling, see “Handling synchronous errors in an application” on
page 58.
Asynchronouserrors are run-time errors that occur at various points during runtime; they generate events and event
listeners catch them. An asynchronous operation is one in which a function initiates an operation, but doesn’t wait
for it to complete. You can create an error event listener to wait for the application or user to try some operation.
If the operation fails, you catch the error with an event listener and respond to the error event. Then, the event
listener calls an event handler function to respond to the error event in a useful manner. For example, the event
handler could launch a dialog box that prompts the user to resolve the error.
Consider the file-upload synchronous error example presented earlier. If you successfully call the browse()
method before beginning a file upload, Flash Player would dispatch several events. For example, when an upload
starts, the open event is dispatched. When the file upload operation completes successfully, the complete event is
dispatched. Because event handling is asynchronous (that is, it does not occur at specific, known, predesignated
times), use the addEventListener() method to listen for these specific events, as the following code shows:
Last updated 6/6/2012
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