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You must check the return value and, only if nil do you consider the contents of the error. (Also, there is no requirement to initialize error to nil in the caller.) I can't really see anything wrong with checking the error pointer, however. Try our newsletter Sign up for our newsletter and get our top new questions delivered to your inbox (see an example). I just pass it in and if the call failed for whatever reason I have an NSError object to explain what the problem was. Check This Out

This tells the compiler that I want to change what the pointer to pointer is pointing to. However, I could just as easily have done this: Objective-C if (!success) { NSLog(@"%@:%s Error saving context: %@", [self class], _cmd, [error localizedDescription]); return; } 1234 if (!success) {NSLog(@"%@:%s Error saving Doing laundry as a tourist in Paris Why won't a series converge if the limit of the sequence is 0? For this reason I wouldn't recommend using exceptions @try/@catch just to test whether a method worked correctly.

Objective C Nserror

This pattern is commonly used in asynchronous delegate-based APIs. What is the difference (if any) between "not true" and "false"? This is exactly what the Apple docs say on using NSError vs Exceptions.

share|improve this answer answered Jul 23 '11 at 17:44 NSResponder 15.9k72441 To complete this answer: exceptions are only to catch non recoverable mistakes. Join them; it only takes a minute: Sign up What are the best practices for exceptions/returning NO/nil in Objective-C? To do this I first constructed an NSMutableDictionary that contains all of the information about the failure. Objective-c Throw Exception Related 103Best practices for exception management in Java or C#2What to Return?

Handling errors Cocoa on Mac OS X has a quite thorough error-handling path. Objective C Try Catch Example Is that the best approach? Therefore if there is an exception that can be caught -- it should be caught. As for your last point, not everything that Apple does is gold.

Subscribed! Ios Exception Handling Best Practices Read the blockquote at the Exception Programming Topic: developer.apple.com/library/mac/#documentation/cocoa/Concept‌ual/… –Jano Jul 23 '11 at 17:49 add a comment| Your Answer draft saved draft discarded Sign up or log in Sign Exceptions are a huge pain when you don't have garbage collection, which is new in Objective-C and still not available on the iPhone. What to do when you've put your co-worker on spot by being impatient?

Objective C Try Catch Example

It is not meant to be perfect coding practice and that everyone must follow my lead. Anyone who has written Java code for any length of time knows the true hell that is try/catch. Objective C Nserror First some code to demonstrate how Apple uses NSError: Objective-C NSError *error = nil; BOOL success = [myContext save:&error]; if (!success) { [NSApp presentError:error]; return; } //Continue processing 1234567 NSError *error Exception Handling In Ios Objective C So, how do I decide when use which, and how to handle exceptions and unexpected return values?

up vote 7 down vote Exceptions should be used as little as possible in Objective-C. Conclusion This article will be followed up with another one detailing some of the more interesting things that you can do with NSError objects. Browse other questions tagged objective-c exception exception-handling return-value or ask your own question. It indents my code all to hell, is difficult to follow and even more difficult to debug. Objective C Try Catch Finally

Just because they do something does not make it right. So I guess even an experienced iOS developer like me can learn something new every now and then :) –Wolfgang Schreurs Jul 24 '11 at 9:21 add a comment| up vote Oops… Introduction to NSError Fortunately, there is a better solution. this contact form One minor point - the convention seems to be that callers who don't care about the details of any errors are allowed to pass NULL for the *NSError pointer.

Marcus Zarra says: April 6, 2008 at 9:13 am Icy, Yes it should be if (error) and it is correct in the project. Objective C Try Catch Exc_bad_access Realize that this is an example of using NSError. What was 1?

There are many weaknesses in the code that if corrected would cloud the message.

Find the 2016th power of a complex number Print the tetration Is there a formal language to define a cryptographic protocol? current community chat Stack Overflow Meta Stack Overflow your communities Sign up or log in to customize your list. Read the Error Handling Programming Guide for more information. Nsexception To Nserror On iOS, the NSError class still exists, but there aren't the same convenience methods to handle errors.

To update the pointer that the passed in pointer is pointing to I need to include an asterisk before the name of the variable. NSObject *object = [set anyObject] if (!object) { *error = [NSError errorWithDomain:@"AppDomain" code:1000 userInfo:nil]; return nil; } return object; } // and then we use the function like this - (void)test I find myself often re-coding a method after I realize that I need to handle one error condition or another. http://brecnc.org/objective-c/objective-c-objc-msgsend-error.html Normally when a message is sent, a pointer to the object is being passed in the message.

As with NSError, exceptions in Cocoa and Cocoa Touch are objects, represented by instances of the NSException class, You can use @try { // do something that might throw an exception Sorry for the delay in accepting it — had to learn and try all of it first. –Max Yankov Jul 25 '11 at 13:11 I'm glad you did! –jtbandes USB in computer screen not working What is this strange almost symmetrical location in Nevada? This is denoted with the single asterisk(*) in the method signature such as Objective-C -(void)appendString:(NSString*)newString 1 -(void)appendString:(NSString*)newString This is different then passing a pointer to a pointer.

If you wish to understand how this works, I would suggest the double indirection wikipedia article as a great starting point. I dislike try/catch blocks and consider them to be a bad design choice. Another minor point - you're checking if error was set to detect an error. Passing Pointers to Pointers Using the NSError class in the above example is quite simple.

Errors Errors are typically used in three ways: Delegate methods An object can simply pass an NSError to its delegate in a designated error-handling callback: - (void)myObject:(MyObject *)obj didFailWithError:(NSError *)error; The Hopefully this taste will highlight the usefulness of this method of error handling and how it is an improvement over both try/catch blocks and return codes. There are exceptions, but also there are situations where functions are just supposed to return nil in case of something going wrong.