ACTIONSCRIPT 3 Developer’s Guide en

ACTIONSCRIPT 3.0 DEVELOPER’S GUIDE
Handling errors
Handling synchronous errors in an application
Flash Player 9 and later, Adobe AIR 1.0 and later
The most common error handling is synchronous error-handling logic, where you insert statements into your code to
catch synchronous errors while an application is running. This type of error handling lets your application notice and
recover from run-time errors when functions fail. The logic for catching a synchronous error includes
try..catch..finally statements, which literally try an operation, catch any error response from the Flash runtime,
and finally execute some other operation to handle the failed operation.
Using try..catch..finally statements
Flash Player 9 and later, Adobe AIR 1.0 and later
When you work with synchronous run-time errors, use the try..catch..finally statements to catch errors. When
a run-time error occurs, the Flash runtime throws an exception, which means that it suspends normal execution and
creates a special object of type Error. The Error object is then thrown to the first available catch block.
The try statement encloses statements that have the potential to create errors. You always use the catch statement
with a try statement. If an error is detected in one of the statements in the try statement block, the catch statements
that are attached to that try statement run.
The finally statement encloses statements that run whether an error occurs in the try block. If there is no error, the
statements within the finally block execute after the try block statements complete. If there is an error, the
appropriate catch statement executes first, followed by the statements in the finally block.
The following code demonstrates the syntax for using the try..catch..finally statements:
try
{
// some code that could throw an error
}
catch (err:Error)
{
// code to react to the error
}
finally
{
// Code that runs whether an error was thrown. This code can clean
// up after the error, or take steps to keep the application running.
}
Each catch statement identifies a specific type of exception that it handles. The catch statement can specify only error
classes that are subclasses of the Error class. Each catch statement is checked in order. Only the first catch statement
that matches the type of error thrown runs. In other words, if you first check the higher-level Error class and then a
subclass of the Error class, only the higher-level Error class matches. The following code illustrates this point:
Last updated 6/6/2012
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