Episode 4 - Objective-C

This Podcast will cover the Introduction to Objective-C as described in “Cocoa Programming for Mac OS X” by Aaron Hillegass. This is the first part of the podcast that covers the chapter 3. There a lot of things I needed to say about Objective-C and even while trying to make it as short as possible, I was still unable to fit within 30 minutes. I have already recorded most of the 2nd part of this chapter’s podcast, so in a few days expect to see the conclusion. Topics covered today include Foundation tool, Memory management, and some basic Foundation classes.

Here are the show notes for this Episode: Show Notes
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Show Notes:

Introduction to Objective-C
Episode 4
This episode introduces Objective-C programming language
Chapter 3 - Objective-C
Introduction to Objective-C
Episode 4
This episode introduces Objective-C programming language
Chapter 3 - Objective-C

Podcast Announcements

• Thanks for your comments
• Julien, Mike, Eric, and others
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Call for Help

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• Suggestions for Topics
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Podcast Conventions

The Following are Some Conventions for the Screencast

I’m trying to follow WWDC Presentations Format - Use Forums to Comment

Conventions

Method, Class, and Sub-Section Names

- (void)setRadius:(id)sender {
radius = [sender floatValue];
[self setNeedsDisplay:YES];
}
- (void)setRadius:(id)sender {
radius = [sender floatValue];
[self setNeedsDisplay:YES];
}
- (void)setRadius:(id)sender {
radius = [sender floatValue];
[self setNeedsDisplay:YES];
}
Code
Section

Code with
Highlights

Code with
Discussion

Console Applications

Use of Xcode for creation of Console Application

Xcode Foundation Tool

• Pure Objective-C Application
• Foundation Framework
• Foundation Tool/Project in Xcode

Demo

Creating Xcode Foundation Tool Projects

Objective-C Syntax

Getting Used to Objective-C

Creating and Using Instances

NSMutableArray *foo;
foo = [NSMutableArray alloc];
NSMutableArray *foo;
foo = [NSMutableArray alloc];
[foo init];
Allocation without Initialization

Initialize Object before Using

NSMutableArray *foo;
foo = [[NSMutableArray alloc] init];
Combined Initialization

Calling Methods

Method Calls in C and Java

x.insertObject(bar, i);
[x insertObject:bar atIndex:i];
[foo center];
[foo addObject:bar];
Method Calls in Objective-C

Non Descriptive C

if (x.intersectsArc(35.0, 19.0, 23.0, 90.0, 100.0))
vs.

if ([x intersectsArcWithRadius: 35.0centeredAtX: 19.0
Y: 23.0
fromAngle: 90.0toAngle:100.0])
In Objecive-C

Demo

First Foundation Tool application - Lottery

Memory Management

Reference Counting in Objective-C
Retain Count, Releasing, and Retaining

Reference Counting

TrainerOwerGroomretainCount=3Dog

Reference Counting

TrainerOwerGroomretainCount=2Dog

Reference Counting

TrainerOwerGroomretainCount=1Dog

TrainerOwerGroomretainCount=0DogRelease
TrainerOwerGroomretainCount=0DogRelease

Retain and Release

[foo retain];
for (i=0; i<10; i++) {
newNumber = [[NSNumber alloc] initWithInt:(i*3)];
[array addObject:newNumber];
[newNumber release];
}
retain message
release message

Sending Messages to nil

safe to send to nil

id foo;
foo = nil;
[foo count];
id foo = [[NSMutableArray aloc] init];
[foo release];
[foo count];
id foo = [[NSMutableArray aloc] init];
[foo release];
foo = nil;
[foo count];
not safe

now it is safe again

NSObject, NSArray, etc.

Hierarchy and the difference between Mutable and Regular Containers

Object hierarchy

• NSObject is the root of all objects in Cocoa
-(id)init+(id)new-(NSString *)description-(id)retain-(void)release-(void)dealloc-(BOOL)isEqual:(id)anObject

NSArray Class

• NSArray is the first of collection classes available in Foundation Framework
• NSArray is immutable
-(unsigned)count-(id)objectAtIndex:(unsigned)i-(id)lastObject-(BOOL)containsObject:(id)anObject-(unsigned)indexOfObject:(id)anObject
// If object is not found NSNotFound is returned

NSMutableArray Class

• NSMutableArray is editable (inherited) version of NSArray
• NSArray has mutableCopy method
• Adds the Ability to add and remove objects
-(void)addObject:(id)anObject-(void)addObjectsFromArray:(NSArray *)otherArray-(void)insertObject:(id)anObject atIndex:(unsigned)index-(void)removeAllObjects-(void)removeObject:(id)anObject

NSString Class

• NSString can hold Unicode characters
• Uses @”...“ format for distinguishing with C-strings
-(id)initWithFromat:(NSString *)format, ... // Like sprintf-(unsigned)length-(NSString *)stringByAppendingString:(NSString *)aString
// There are many other methods -- see documentation

Demo

Creating Custom Classes

More about Memory Management

Autoreleased Objects

Autorelease

- (NSString *)description {
NSString *result;
result=[[NSString alloc] initWithFormat:@”%@ = %d and %d”,
entryDate, firstNumber, secondNumber];
return result;
}
- (NSString *)description {
NSString *result;
result=[[NSString alloc] initWithFormat:@”%@ = %d and %d”,
entryDate, firstNumber, secondNumber];
[result release];
return result;
}

Autorelease

- (NSString *)description {
NSString *result;
result=[[NSString alloc] initWithFormat:@”%@ = %d and %d”,
entryDate, firstNumber, secondNumber];
[result autorelease];
return result;
}

Autorelease Rules

• Objects created by alloc, new, copy, or mutableCopy have retain
count of 1 and are not in autorelease pool
• If you get an object by any other method, assume that it has s retain
count of 1 and is in the autorelease pool. If you do not with to be
deallocated with the current autorelease pool, you must retain it

3 Ways to Retain Objects

- (void)setFoo:(NSCalendarDate *)x {
[x retain];
[foo release];
foo = x;
}
- (void)setFoo:(NSCalendarDate *)x {
if(foo !=x){
[foo release];
foo = [x retain];
}
“Retain, then Release”

“Check before change”

3 Ways to Retain Objects (cont.)

- (void)setFoo:(NSCalendarDate *)x {
[foo autorelease];
foo = [x retain];
}
“Autorelease old Value”

Demo

NSCalendarDate and custom Initializers

Demo

Debugger

Summary

• Basic Objective-C constructs
• Initializers
• Basic Containers and NSString
• Memory Management
• Foundation Tool
• Basic Debugging

Demo

Chapter 3 Challenge Solution