These are the 8 biggest foul-ups that I wish I had known before I started learning Objective-C. Hopefully you'll learn something here that will prevent you from making an idiotic mistake I already made.

If you need to store a reference to an NSManagedObject outside of an NSManagedObjectContext, then you'll need to convert NSManagedObjects to URIs and back again. At first glance it looks like a simple method will do all the work for you but in reality you must be careful when getting the object back. I'll show you the way to convert an object to a URI and get it back safely.

Is this the E4X of Cocoa?

Now I come from a flex world, so dont hurt me when I say this was a tough thing to figure out for me. Typically in Flex, you can create handlers fairly easily. Ok, really easily. For the iPhone, I wanted to basically have the same custom handler “handle” my operation. Hmmm….enter the delegate.

Objective-C's unique syntax results in unique ways of making mistakes. In this post, I look at the compiler warnings and errors GCC outputs when you make mistakes or potential mistakes in your Objective-C syntax and show you how to fix them.

I will show you how to use object forwarding to record any message in an NSInvocation, by simply sending the message to an object. Unlike techniques shown elsewhere, this will allow you to record any message, including NSObject messages and even the forwarding messages themselves.

It's a lot easier to get your data out of Core Data than the documentation will tell you. This simple 1-line fetch will work just as well as Apple's suggested 10-line approach for most uses.

Recent years have seen an end to the continual rise of processor clock speeds, and a move toward multi-core as the way forward. This trend has implications for software developers, because in order to make use of the extra processing power available in multi-core systems, you have to rewrite parts of your application to work concurrently. Even if you do not need that extra number-crunching performance in your app, there are many operations—such as downloading files—that can be more efficient when performed simultaneously.

Many new iPhone developers are coming from backgrounds in higher level languages (web, javascript, actionscript, etc), where you don't have to think about things like garbage collection or concurrent processes. You can get along programming for the iPhone without ever touching a thread, but to optimize performance on almost any application it is a must. Threading can be a little tricky so I have put together a simple example to help break the ice.

This sample shows how to use UITableView through a progression of increasingly advanced applications that display information about time zones... The fifth example is an extension of the fourth. It displays even more information about each time zone, such as the time and relative day in that time zone. Its shows how you can create a custom table view cell that contains a custom view that draws its content in -drawRect:.

Scrolling is the primary method of interaction on the iPhone. It has to be fast. It has to be fast. More than a few developers have asked me how I do it in Tweetie, so I figured I would share a really fast and really clean technique people can adopt in their own apps.

The code examples for the iPhone SDK show only how to construct your table cells programatically. If you want to use InterfaceBuilder to make a proper layout which might also be resizable etc. you can use this ViewFactory to handle the creation and reusage of your table cells.