Cocoa Programming for Mac OS X (Ch 1-5)

Earlier this week I purchased this book: Cocoa Programming for Mac OS X since I wanted to get an introduction on how to develop native applications for OS X. It’s the most recently published one on the issue and got mentioned on MacRumors.

In a series of small posts I’ll put down some notes for myself here and anyone who is interested can read along.

Chapter one gives you some background on the language, what tools will be used throughout the book and explains the different kinds of frameworks available in Cocoa. Nothing special here, I want to write code!?

And there’s chapter two, the author guides you through your first Objective-C program. The interface of XCode and Interface builder (IB) are explained. I was surprised to read that any method you write is public and every instance variable is protected. Also instance fields which are connected through the IB are called outlets and you designate them accordingly in your header file. Methods that can be used by user interface objects are called actions.

#import <Cocoa/Cocoa.h>
 
@interface Foo : NSObject 
{ 
    IBOutlet NSTextField *textField; 	
}  
 
- (IBAction)seed:(id)sender; 
 
- (IBAction)generate:(id)sender;

The – before the two method declarations indicate that it’s an instance method, class methods are designated with a +. The IBAction and IBOutlet are hints for the IB. NSObject is the base class for every other object. The id ‘type’ (don’t know if I am allowed to call it that way) is a pointer to basically anything.

Chapter three digs a little deeper on objects and classes. Calling methods on objects looks a bit different if you come from a Java or C# background.

MyClass* myInstance = [[MyClass alloc] init]; 
 
[myInstance doStuff]; 
 
[myInstance doStuffWith:bar];  
 
[myInstance doStuffWith:bar using:foo];

The first line first calls the constructor and init method. Both are inherited from NSObject and on the second line I call the doStuff method on myInstance. It takes some getting used to, also note the naming convention if you’re a .Net programmer methods start with a capital. Method names are also called selectors. On the third line I assume I’ve an other object called bar and it illustrates how you pass parameters with method calls. Finally the last line illustrated how multiple arguments are passed along.

I raised an eyebrow when I read that if you call a method of on objects which points to nil (null), no exception will be raised. Sure, it allows you to omit those tedious if(!= null) checks but I’ll probably pull out my hair when I’m writing more real life application and it’s not responding the way it should.

One final note for this chapter, calling methods of your base type is done in the Objective-C world by using the super keyword.

Chapter four talks about memory management. This was fairly new for me, I knew about it but I’ve only written programs in .Net (C#, Vb.Net, managed C++) or J2EE (Java) and both environments come with the garbage collector (GC) which manages memory for you. Mac OSX 10.5 introduced the GC as well, but it’s an option. If you turn it on your application will only run on 10.5 and later, so if you want to target previous versions you’ll have to release and retain yourself.

It was an interesting read, I never had seen an example of how memory can be managed in code you write. I’ll probably just turn the GC on for stuff I write. The chapter ends with stating that you should now have a basic understanding of Objective-C and Cocoa and that the next chapters will focus on the different frameworks you can use to build your applications.

Chapter five introduces some user interface components available in the IB (buttons, textboxes,…), nothing big here although I encourage you to write the challenge application. Challenges in the book are exercises which you should be able to write.

Attached you find the challenge exercise from chapter five (countline), the guided application (speakline) also from chapter five and the lottery application from chapter three and four.

CountLine.zip (55.52 kb)

lottery.zip (16.43 kb)

SpeakLine.zip (52.62 kb)

Also I apologize for the layout of the code in this post I’ll fix that as soon as I can, Objective-C isn’t supported by default 🙂 .

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