ADOBE® FLEX® 3: PROGRAMMING ACTIONSCRIPT™ 3.0

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Chapter 9: Handling errors

To “handle” an error means you build logic into your application that responds to, or fixes, an error, generated either

when an application is compiled or when a compiled application is running. When your application handles errors,

something occurs as a response when the error is encountered, as opposed to no response and whatever process

created the error failing silently. Used correctly, error handling helps shield your application and its users from

otherwise unexpected behavior.

However, error handling is a broad category that includes responding to many kinds of errors that are thrown during

compilation or at run time. This chapter focuses on how to handle run-time errors, the different types of errors that

can be generated, and the advantages of the new error-handling system in ActionScript™ 3.0. This chapter also

explains how to implement your own custom error-handling strategies for your applications.

Contents

Basics of error handling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 165

Types of errors. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 167

Error handling in ActionScript 3.0. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 169

Working with the debugger versions of Flash Player and AIR. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 170

Handling synchronous errors in an application . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 171

Creating custom error classes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 175

Responding to error events and status. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 175

Comparing the Error classes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 178

Example: CustomErrors application. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 183

Basics of error handling

Introduction to error handling

A run-time error is something that goes wrong in your ActionScript code that stops the ActionScript content from

running in Adobe® Flash® Player or Adobe® AIR™. To ensure that your ActionScript code runs smoothly for users,

you must write code in your application that handles the error—that fixes it, works around it, or at least lets the user

know that it’s happened. This process is called error handling.

Error handling is a broad category that includes responding to many kinds of errors that are thrown during compi-

lation or at run time. Errors that happen at compile time are often easier to identify—you must fix them in order to

complete the process of creating a SWF file. This chapter doesn’t discuss compile-time errors; for more information

on writing code that doesn’t contain compile-time errors, see “ActionScript language and syntax” on page 33 and

“Object-oriented programming in ActionScript” on page 84. This chapter focuses on run-time errors.

Run-time errors can be more difficult to detect, because in order for them to occur the erroneous code must actually

be run. If a segment of your program has several branches of code, like an

if..then..else statement, you must test

every possible condition, with all the possible input values that real users might use, in order to confirm that your

code is error-free.