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NSAssertionHandler Class Reference

Overview

NSAssertionHandler objects are automatically created to handle false assertions. Assertion macros, such as NSAssert and NSCAssert, are used to evaluate a condition, and, if the condition evaluates to false, the macros pass a string to an NSAssertionHandler object describing the failure. Each thread has its own NSAssertionHandler object. When invoked, an assertion handler prints an error message that includes the method and class (or function) containing the assertion and raises an NSInternalInconsistencyException.

You create assertions only using the assertion macros—you rarely need to invoke NSAssertionHandler methods directly. The macros for use inside methods and functions send handleFailureInMethod:object:file:lineNumber:description: and handleFailureInFunction:file:lineNumber:description: messages respectively to the current assertion handler. The assertion handler for the current thread is obtained using the currentHandler class method. If you need to customize the behavior of NSAssertionHandler, create a subclass, overriding the above two methods, and install your instance into the current thread’s attributes dictionary with the key NSAssertionHandler.

Tasks

Handling Assertion Failures

• + currentHandler
• – handleFailureInFunction:file:lineNumber:description:
• – handleFailureInMethod:object:file:lineNumber:description:

Class Methods

currentHandler

Returns the NSAssertionHandler object associated with the current thread.

+ (NSAssertionHandler *)currentHandler

Return Value

The NSAssertionHandler object associated with the current thread.

Discussion

If no assertion handler is associated with the current thread, this method creates one and assigns it to the thread.

Availability

• Available in Mac OS X v10.0 and later.

Declared In

NSException.h

Instance Methods

handleFailureInFunction:file:lineNumber:description:

Logs (using NSLog) an error message that includes the name of the function, the name of the file, and the line number.

- (void)handleFailureInFunction:(NSString *)functionName file:(NSString *)fileName lineNumber:(NSInteger)line description:(NSString *)format, ...

Parameters

functionName

The function that failed.

object

The object that failed.

fileName

The name of the source file.

line

The line in which the failure occurred.

format,...

A format string followed by a comma-separated list of arguments to substitute into the format string. See Formatting String Objects for more information.

Discussion

Raises NSInternalInconsistencyException.

Availability

• Available in Mac OS X v10.0 and later.

Declared In

NSException.h

handleFailureInMethod:object:file:lineNumber:description:

Logs (using NSLog) an error message that includes the name of the method that failed, the class name of the object, the name of the source file, and the line number.

- (void)handleFailureInMethod:(SEL)selector object:(id)object file:(NSString *)fileName lineNumber:(NSInteger)line description:(NSString *)format, ...

Parameters

selector

The selector for the method that failed

object

The object that failed.

fileName

The name of the source file.

line

The line in which the failure occurred.

format,...

A format string followed by a comma-separated list of arguments to substitute into the format string. See Formatting String Objects for more information.

Discussion

Raises NSInternalInconsistencyException.

Availability

• Available in Mac OS X v10.0 and later.

Declared In

NSException.h

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