A property/ivar/outlet was just changed, how do I find out who did it?

I see this post all the time on StackOverflow. The answer is surprisingly simple:

– if you have an ivar, convert it to a property with a synthesize ivar=ivar if needbe to avoid having to prepend a “_” to usages

– write your own setter, and add logic tests and NSLog messages

– put a breakpoint on the NSLog┬ámessage, and run your app

Voila! You app stops when the value changes, and you can see who the offender is!

URL Verifier, Parser, and Scraper in Objective-C

I just updated the second version of my github project, URLFinderAndVerifier. Needing to verify a http URL as it was typed in to toggle an “Accept” button, I searched the web for such a thing, and unfortunately found oodles of them, none of which had any credentials.

Looking closer on another day, I found a site run by Jeff Roberson where he had meticulously worked through RFC-3896, constructing simple regular expressions then combining them to create a full regular expression that should properly parse any valid URL. Note that the standard allows much of what we think of as necessary information to be empty.

So I started with his expressions, then tweaked them slightly to handle more real world conditions, such as forcing a person to enter (the optional) ‘/’ at the start of the path segment (which acts as a end of authority marker).

Using my previous Email verifier test harness, I constructed a test engine that lets you test out various combinations of options. It has three components:

– construct the regular expressions for use in a text file or a NSString constant

– URLSearcher, a class that uses to regular expression to find or verify URLs

– a test app that you use to test various URLs, or “live” input mode


All regular expressions exist in text files that are heavily commented. A pre-processor reads these files and removes comments and extraneous characters (like spaces). This makes the files much more readable and understandable. These partial regular expressions that are used to build a full regular expression based on the options you select in the GUI.

Users can optionally enter Unicode characters, which the regular expression can optionally allow. Given a verified URL, a utility function in URLSearcher converts these syntactically correct strings to ‘%’ encoded ones that fully meet the RFC spec (Europeans should like this!)

Other options are to look for every scheme, or http/https, or http/https/ftp and the ability to spec capture groups to see URL subcomponents: user, host, port, path, query, and fragment.

PS: if you end up using this it would be great if you could give the StackOverflow post an up-arrow.

Tracking system object deallocs

Have you ever had a time when you had a memory leak, but was unsure if the problem were your objects, or that some collection item holding them wasn’t getting dealloced?

Well, now you don’t need to wonder any more: https://github.com/dhoerl/ObjectTracker

This demo project highlights the Tracker class. After creating and initializing say a mutable array, ask Tracker to track it:

[Tracker trackerWithObject:obj msg:@”Some Msg”];

If obj does get dealloc’d, you’ll see a NSLog message in the console. Or, at some point where you think obj should have been dealloced, ask the class for the current list of tracked objects and dump their descriptions to the console.

You probably don’t need this functionality often, but when you need it, its invaluable!