I noticed in several of your NSError article examples, you give the status code number a seemingly random value. I’m fairly sure this is simply to keep the examples short and sweet. I was wondering if, in your production code, you have some header that you include with a bunch of these error codes defined? Is that the best approach?

Thanks for the great blog.

An opinion, no matter what you may think of it, can never be wrong. I dislike try/catch blocks and consider them to be a bad design choice. You are welcome to have your own opinion.

As for my opinion — an application should never crash due to a bug that the developer is aware of. Therefore if there is an exception that can be caught — it should be caught. The only time an application should crash is when something happens totally outside of the developer’s expectations. If the code is throwing an exception then it is within the realm of expectation and therefore should be dealt with.

Realize that this is an example of using NSError. It is not meant to be perfect coding practice and that everyone must follow my lead. It demonstrates how to use the NSError object and the often complex subject of double indirection. There are many weaknesses in the code that if corrected would cloud the message.

As for your last point, not everything that Apple does is gold. Just because they do something does not make it right.

Also, the Cocoa library support you get for NSError is very good. Every Cocoa app should use NSError.

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. I never assign to *error without checking if error is NULL first. I guess this only matters if you’re writing code that might be called by someone else.

Another minor point – you’re checking if error was set to detect an error. But the examples I’ve seen do this by checking for a special value returned by the method, usually nil or NO. From memory this is what the Apple docs recommend. I can’t really see anything wrong with checking the error pointer, however.

Yes it should be if (error) and it is correct in the project. Thanks for catching the typo!

thanks a lot for this post. This is really some valuable information. But shouldn’t it be “if (error)” instead of “if (!error)” in the last listing?

if (!error) { [NSApp presentError:error];

So, if not an error, then present the error.

Thinking about it again, I just want to cry.

/tompa