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Error Objects, Domains, and Codes

Cocoa programs use NSError objects to convey information about runtime errors that users need to be informed about. In most cases, a program displays this error information in a dialog or sheet. But it may also interpret the information and either ask the user to attempt to recover from the error or attempt to correct the error on its own.

The core attributes of an NSError object—or, simply, an error object—are an error domain, a domain-specific error code, and a “user info” dictionary containing objects related to the error, most significantly description and recovery strings. This chapter explains the reason for error objects, describes their attributes, and discusses how you use them in Cocoa code.

Contents:

Why Have Error Objects?
Error Domains
Error Codes
The User Info Dictionary

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