One of the techniques which I have found to be extremely useful are notifications in Objective-C. Using NSNotification to send broadcasts to all objects in your app is something that I did not see in any other language or framework I visited before. Here is a quick recipe to show how to use them.

Think of notifications as a method of informing all your class instances within your app at the same time. Sometimes there is a global change that does not have a single target like you would for a delegate. Without notifications you would have to keep track of all objects to be informed of the change manually, loop through them and call an update method.

To give one useful example: In MyAppSales you can set your main currency so that all amounts get converted into the currency you are used to instead of showing you Japanese Yen. Now what happens if the user chooses a different currency and you have objects like table views, table cells or your own class instances that need to change something whenever the main currency changes. Enter NSNotification and NSNotificationCenter.

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Once you get smart enough to build multiple apps from the same project you probably have to wrap your head around the concept of #define and #ifdef to conditionally activate and deactivate portions of your code. What is somewhat unnerving is that the target build settings change their appearance seemingly uncontrollably and I took a while to work out what triggers this morphing.

The difference lies in what settings you choose in the upper left hand corner of XCode. Only if you select the “Base SDK” setting then the dialog is the most user-friendly.

The build settings for the active target can no be reached by right-click on target, Get Info, build tab. Or alternatively menu option “Project”, “Edit Active Target”. I discovered three places where #define statements can be placed. I am going to show them to you and make a recommendation as well.

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Do you really understand when you need to retain and release some object? And what about autorelease? It took me around 3 months before I grasped when to use autorelease and now it’s second nature to me. But when I needed to explain to a coding buddy I was stumped. I found that my approach was one of feeling rather than knowledge.

So I decided it was time to do an experiment to visualize what happens to the retain count and when an instance is really released. So see what’s happening to our crash test dummy class I made a TestClass that overrides all the important methods so that we get an output to NSLog what is happening.

First I want to demonstrate how the retain counter – present in all Objective-C classes – is used to automatically determine when the instance can be freed from memory. Then I am going to show how to use a factory method which returns an autoreleased instance to make your life easier.

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When transmitting data in the context of the HTTP protocol you often need to encode text in a way that does not interfere with special characters used in URLs. This is of importance if you want to put unicode characters into an URL query but also for simple things like constructing a body for a HTTP POST request. A form post also takes the form fields and puts them into the form that you know from an URL: field=text&another=more. That’s what the HTML content type “application/x-www-form-urlencoded” means.

The first thing that jumps out of the documentation when looking for a standard function to achieve such “URL Encoding” is stringByAddingPercentEscapesUsingEncoding. So that is what I was using for encoding the password for my iTunes Connect class which drives MyAppSales. And until now this worked without a hitch until customer #113 who was the first to use a plus character in his password. The poor guy ended up locking his iTunes account. Sorry!

It turns out that + is an anachronistic special character substitution for a space. I would have expected for it to be encoded properly by the above mentioned method as %20, but this is not the case.

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