Objective c intro (1)

Overview
 Objective-C is an object oriented language.
 follows ANSI C style coding with methods
from Smalltalk
 Flexible almost everything is done at runtime.
Dynamic Binding
Dynamic Typing
Dynamic Linking

Inventors
 Objective-C was invented by two men,
Brad Cox and Tom Love.
 Both were introduced to Smalltalk at ITT in
1981
 Cox thought something like Smalltalk
would be very useful to application
developers
 Cox modified a C compiler and by 1983 he
had a working Object-oriented extension to
C called OOPC.

Development
 Tom Love acquired a commercial copy
of Smalltalk-80 while working for
Schlumberger Research
 With direct access Smalltalk, Love
added more to OOPC making the final
product, Objective-C.
 In 1986 they release Objective-C
through their company “Stepstone”

NeXT and NeXTSTEP
 In 1988 Steve Jobs acquires Objective-
C license for NeXT
 Used Objective-C to build the
NeXTSTEP Operating System
 Objective-C made interface design for
NeXTSTEP much easier
 NeXTSTEP was derived from BSD Unix
 In 1995 NeXT gets full rights to
Objective-C from Stepstone

OPENSTEP API
 Developed in 1993 by NeXT and Sun
 An effort to make NeXTSTEP-like
Objective-C implementation available to
other platforms.
 In order to be OS independent
Removed dependency on Mach Kernel
Made low-level data into classes
 Paved the way for Mac OS X, GNUstep

Apple and Mac OS X
 NeXT is taken over by Apple in 1996
and put Steve Jobs and his Objective-C
libraries to work
 Redesigned Mac OS to use objective-C
similar to that of NeXTSTEP
 Developed a collection of libraries
named “Cocoa” to aid GUI development
 Release Mac OS X (ten), which was
radically different than OS 9, in March
2001

The Cocoa API
 Developed by Apple from NeXTSTEP and
OPENSTEP
 Has a set of predefined classes and types
such as NSnumber, NSstring, Nsdate, etc
.
 NS stands for NeXT-sun
 Includes a root class NSObject where words
like alloc, retain, and release come from

Dynamic Language
 Almost everything is done at runtime
 Uses dynamic typing, linking, and
binding
 This allows for greater flexibility
 Minimizes RAM and CPU usage

To Import or Include?
 C/C++’s #include will insert head.h into
the code even if its been added before.
 Obj-C’s #import checks if head.h has
been imported beforehand.
#import “head.h”

Objective-C
 Is a SUPERSET of C

Primitive data types from C
 int, short, long
 float,double
 char

Operators same as C
 +
 -
 *
 /
 ++
 --

Address and Pointers
 Same as C
 To get address of a variable i
&i
 Pointer
int *addressofi = &I;

Conditionals and Loops
 Same as C/C++
 if / else if/ else
 for
 while
 break
 ontinue
 do-while
for(int i=0; i< 22; i++) {
printf(“Checking i=“@dn”, i);
if(i+90 == i*i)
{ break;}

for in loop
 Introduced in Objective-C 2.0 (“fast enumeration”)
for(Item_Type *item in Collection_of_Items) {
//do whatever with the item
Nslog(@” Looking now at %@”, item);
}
Note: %@ in the NSLog
converts whatever is passed
(in this case item) to a string

Functions
 Same as C/C++
 return_type functionName(type v1, type v2, ….)
{ //code of function
}
Example
void showMeInfo(int age)
{
printf(“You are %d years old”, age); //or use NSLog()
}

Global and static variables
 Same as C/C++
 Global variables defined at top of file
 For static variables use keyword static before it
static in CurrentYear = 2013;

Functions --- pass by reference
 Same as C/C++
return_type functionName(type v1, type *v2, ….)
{ //code of function
}
Example – call above
int v1 = 2;
int v2 = 3;
functionName(v1, &v2);

Main Funciton –like C++
#import <whatever/what.h>
int main(int argc, const char *argv[])
{
@autoreleasepool {
//your code here*******
//you can have C code if you wish or Objective-C
return 0;
}
}
NOTE: Latest version of Objective-C uses Automatic
Reference Counting (kind of like automatic garbage collection)
----to handle getting rid of not needed items in memory (avoiding
memory leaks). YEAH! AUTOMATIC!
-----like Java this way
@autoreleasepool in a needed annotation around your main
block of code to “enable” this

IMPORTANT --- we are doing iOS
applications NOT mac OS applications
We will be doing iOS application that have a different
framework called Model View Controller ----
But, for some examples to learn concepts of Objective-C
we will show some basic main.m files with main functions
that are not iOS programs!!!
We will learn iOS soon!

Main Function –like C++
#import <whatever/what.h>
int main(int argc, const char *argv[])
{
@autoreleasepool { //takes care of “automatic release of not needed items
//static method date with no parameters is invoked on NSDate class
NSDate *now = [NSDate date]; //this will generate a new instance of NSDate with current time
NSLog(@”The new date lives at %p”, now); //Objective-C function that is like printf to console
double seconds = [now timeIntervalSince1970] //call timesInterrval* method on now object
NSLog(@”It has been %f seconds since 1970”, seconds);
NSDate *later = [now dateByAddingTimeInterval:100000]; //pass 100000 parameter to method
NSLog(@”In 100,000 seconds will be %@”, later); //%@ means print as string
return 0;
}
}

Non-GUI – text output
 Two standard functions you see used
 printf() – same as C
○ printf(“Hi Lynne”); //this is actual C code
 NSLog()
○ NSLog(@”Hi Lynne”); //this is strictly Objective-C

Classes
 Have both definition file and
implementation file : classname.h and
classname.m
 Similar to how have .h and .cpp in C++

Declaring a class in
ClassName.h#import <Cocoa/Cocoa.h>
@interface ClassName : Parent {
//class variables
int age;
NSString name;
}
// methods declared
-(void)setAge:(int)number;
-(void)setName:(NSString)n;
-(int)getAge;
-(NSString)getName;
@end
#import <standardimports.h>
#import “local-your-otherfiles.h”
@interface ClassName: Parent {
//class variables
}
//methods
-(return_type) methodName:(type)param1, (type) param2;
@end

Declaring methods
C++ syntax
Objective-C syntax
void function(int x, int y, char z);
Object.function(x, y, z);
-(void) method:(int)x, (int)y, (char)z;
[Object function:x, y, z];
-(return type) function_name: (type) p1, (type) p2, ***;Apply function to Object
passing parameters x,y,z

Whats this + and – stuff?
 When declaring or implementing
functions for a class, they must begin
with a + or -
 + indicates a “class method” that can
only be used by the class itself. (they are
like static methods in Java invoked on class itself)
 - indicates “instance methods” to be
used by the client program (public
functions) –invoked on an object / class
instance . (they are like regular methods in
Java invoked on object)

Class Implementation File
(ClassName.m)
#import “ClassName.h”
@implementation ClassName
-(void)setAge:(int)number
{ age = number; }
-(void)setName:(NSString)n
{ name = n; }
-(int)getAge
{ return age; }
-(NSString)getName
{ return name; }
@end
Remember our ClassName.h
#import <Cocoa/Cocoa.h>
@interface ClassName :
Parent {
//class variables
int age;
NSString name;
}
// methods declared
-(void)setAge:(int)number;
-(void)setName:(NSString)n;
-(int)getAge;
-(NSString)getName;
@end

Class Declaration (Interface)
#import <Cocoa/Cocoa.h>
@interface Node : NSObject {
Node *link;
int contents;
}
+(id)new;
-(void)setContent:(int)number;
-(void)setLink:(Node*)next;
-(int)getContent;
-(Node*)getLink;
@end
Node.h
Class is Node who’s
parent is NSObject
{ class variables }
+/- private/public methods
of Class
Class variables are private

Class Definition (Implementation)
#import “Node.h”
@implementation Node
+(id)new
{ return [Node alloc];}
-(void)setContent:(int)number
{contents = number;}
-(void)setLink:(Node*)next {
[link autorelease];
link = [next retain];
}
-(int)getContent
{return contents;}
-(Node*)getLink
{return link;}
@end
Node.m
Like your C++
.cpp file
>>just give
the methods
here

Creating class instances
ClassName *object = [[ClassName alloc] init];
ClassName *object = [[ClassName alloc] initWith* ];
 NSString* myString = [[NSString alloc] init];
 Nested method call. The first is the alloc method called on NSString itself.
This is a relatively low-level call which reserves memory and instantiates
an object. The second is a call to init on the new object. The init
implementation usually does basic setup, such as creating instance
variables. The details of that are unknown to you as a client of the class.
In some cases, you may use a different version of init which takes input:
ClassName *object = [ClassName method_to_create];
 NSString* myString = [NSString string];
 Some classes may define a special method that will in essence call alloc followed by
some kind of init
Creating an Object

Object ---invoking a method,
the basics
 Objective-C uses a Message Approach

Messages ---really weird (new) syntax
 Almost every object manipulation is done
by sending objects a message
 Two words within a set of brackets, the
object identifier and the message to send.
Like C++ or Java’s Identifier.message()
[Identifier message ]

Setting values for class variables of
an object ---- THROUGH methods
[object methodName];
[object
setXXXMethod:value1];
[object
setYYYYMethod:value2];

C++ VS. Objective-C
 Adds OOP,
metaprogramming
and generic
programming to C
 Comes with a std
library
 Has numerous uses
 Large and complex
code for OOP
 Only adds OOP to C
 Has no standard
library; is dependant
on other libraries
 Mostly used for
application building
 Simpler way of
handling classes
and objects

Keyword: id
 The word ‘id’ indicates an identifier for an
object much like a pointer in c++
 This uses dynamic typing
 For example, if Pen is a class…
extern id Pen;
id myPen;
myPen = [Pen new ];
id work like pointers to objects.

Memory Allocation
 Objects are created dynamically through
the keyword, “alloc”
 Objects are automatically deallocated in
latest Objective-C through automatic
reference counting

Automatic Reference Counting
 Objective C uses ‘AUTOMATIC reference
counting' as memory management
 keeps an internal count of how many times
an Object is 'needed'.
 System makes sure that objects that are
needed are not deleted, and when an
object is not needed it is deleted.

iOS programs and
@autoreleasepool
 You will notice (later when you learn)
your iOS applications are setup in
Xcode (the IDE) with @autoreleasepool
setup
 This insures automatic release of
unneeded items will take place for you.

linkList class
#import "linkList.h"
@implementation linkList
+(id)new
{return [linkList
alloc];}
-(void)insert:(int)value
{
id temp = [Node new];
[temp
setContent:value];
[temp setLink:head];
head = [temp retain];
[temp release];
}
-(void)append:(int)value {
id last = [head getLink];
while ([last getLink] !=
nil)
{last = [last getLink];}
id temp = [Node new];
[temp setContent:value];
[last setLink:temp];
[temp release];
}
-(void)remove {
id temp = head;
head = [head getLink];
[temp release];
}
-(int)getValue {
return [head
getContent];}
@end
linkList.m
Class linkList is child of
previous Node class
(not showing .h file for brevity)

Stack class (child of linkList)
#import "linkList.h”
@interface Stack : linkList
{}
+(id)new;
-(void)push:(int)value;
-(int)pop;
@end
#import "stack.h”
@implementation Stack
+(id)new
{return [Stack alloc];}
-(void)push:(int)value
{[self insert:value];}
-(int)pop {
int ret = [self getValue]; //getValue metho
of parent linkList
[self remove]; //remove method of parent
linkList
return ret;
}
@end
stack.h stack.m
self is like the C++/Java word this.
Remember alloc creates the
object in memory

Example: main.m
#import "stack.h”
int main(){
Stack *s = [Stack new];
[s push:1];
[s push:2];
printf("%dt", [s pop]);
[s push:3];
[s release];
return 0;
}
Run the program :
2 3 1
new is method defined in Stack class
that simply that calls [Stack alloc]
--- done for convinience
Note only need to import “stack.h” because
stack imports LinkList.h which imports Node.h
which imports cocoa.h
release is method to release this
object s explicitly from memory

Primitive data types
 int, short, long
 float,double
 char
 BOOL = means boolean

NSInteger and NSUnteger
NSInteger number; (Like long in C)
NSUItneger another; (Like unsigned long in C)
Objective-C data types that are 32-Bits on 32-
Bit platforms and 64-bits on 64-bit platforms

NSString
NSString *theMessage = @”hello world”;
Number of characters in a string
○ NSUInteger charCount = [theMessage length];
Test if 2 strings equal
○ if([string_var_1 isEqual: string_var_2])
{ //code for equal case }

String literal in Objective-C
 Begins with the @ symbol
 @”Lynne Grewe”;
Some Examples
NSString *myString = @”Hello World”;
int len = [myString length];
OR
int len = [@”Hello World” length];
OR
NSString *myString = [[NSString alloc] initWithString:@”Hello World”];
int len = [myString length];
This is like “Lynne Grewe” in most other languages

Formatting Strings in output
NSLog
int a = 1;
float b = 33.22;
char c = ‘A’;
NSLog(@”Integer %d Float: %f Char: %c”, a, b, c);

NSString ---not changeable
 International (any language) strings using Unicode.
 Compiler will create an NSString for you using @“foo”
notation.
 An NSString instance can not be modified! They are
immutable.
 Usual usage pattern is to send a message to an NSString
and it will return you a new one.
 self.display.text = [self.display.text stringByAppendingString:digit];
 self.display.text = [NSString stringWithFormat:@“%g”, brain.operand]; // class method
 Tons of utility functions available (case conversion, URLs,
substrings, type conversions, etc.).
Used throughout iOS instead of C language’s char * type.

NSMutableString ---changeable
 Mutable version of NSString. Somewhat rarely used.
 Can do some of the things NSString can do without creating
a new one (i.e. in-place changes).
NSMutableString *ms = [[NSMutableString alloc] initWithString:@“0.”];
NSMutableString *ms = [NSMutableString stringWithString:@“0.”]; // inherited from NSString
[ms appendString:digit];

NSNumber
 Object wrapper around primitive types like int,
float, double, BOOL, etc.
NSNumber *num = [NSNumber numberWithInt:36];
float f = [num floatValue]; // would return 36 as a float (i.e. will convert types)
 Useful when you want to put multiple numeric
primitive types in a collection (e.g. NSArray or
NSDictionary).

NSValue
 Generic object wrapper for other non-
object data types.
CGPoint point = CGPointMake(25.0, 15.0); // CGPoint is a C struct
NSValue *pointObject = [NSValue valueWithCGPoint:point];

NSData
 “Bag of bits.” Used to
save/restore/transmit data throughout
the iOS SDK.

NSDate
 “Used to find out the time right now or to
store past or future times/dates.
 See also NSCalendar,
NSDateFormatter, NSDateComponents.

NSArray – holds fixed array of
points to objects
NSArray *thearray = [NSArray arrayWithObjects:o1,o2,o3,o4, nil];
//get element
[thearray objectAtIndex:0]; //element at index 0
Example
NSDate *now = [NSDate date];
NSDate *tomorrow = [now dateByAddingTImeInterval:24.0*60.0*60.0]; //add a day
NSDate *yesterday = [now dateByAddingTimeInterval:-24.0*60.0*60.0]; //minus a day
//array of Dates
NSArray *dateList = [NSArray arrayWithObjects:now, tomorrow, yesterday];
//get elements in array
NSDate *first = [dateList objectAtIndex:0];
Methods are:
count = gets number of items in array
objectAtIndex:i = returns element i of array (starting from 0)
Note: you can not add or remove a pointer from an NSArray
---fixed once created

NSArray – cycle through with for
loop
//array of Dates
NSUInteger dateCount = [dateList count];
for(int i=0; i<dateCount; i++)
{ NSDAte *d = [dateList objectAtIndex:i];
NSLog(@” Date is %@”, d);
}
Methods are:
count = gets number of items in array
objectAtIndex:i = returns element i of array (starting from 0)

NSArray – cycle through with for
loop OPTION 2
//array of Dates
For(NSDate *d in dateList)
{ NSDAte *d = [dateList objectAtIndex:i];
NSLog(@” Date is %@”, d);
}
This is a “for in” loop --- convinient

NSMutableArray – changeable array
of pointers to objects.
NSMutableArray *thearray = [NSArray arrayWithObjects:o1,o2,o3,o4, nil];
//get element
[thearray objectAtIndex:0]; //element at index 0
Example
//array of Dates
NSMutableArray *dateList = [NSMutableArray array];
//set elements
[dateList addObject:now];
[dateList addObject:tomorrow];
[dateList addObject:yesterday];
Methods are:
array = gets empty NSMutableArray
addObject:obj = adds as next element the obj
to array
Note: you can add or remove a pointer from an NSMutableArray

NSMutableArray – adding element
at Index location
[arrayName insertObject:obj atIndex:i]
Example -- put in at beginning of array
[dateList insertObject:yesterday atIndex:0]

NSMutableArray – removing an
element
[arrayName removeObjectAtIndex:i]
Example
[dateList removeObjectAtIndex:0] //get rid of 1st
element

NSDictionary
 Immutable hash table. Look up objects using a
key to get a value.
+ (id)dictionaryWithObjects:(NSArray *)values forKeys:(NSArray *)keys;
+ (id)dictionaryWithObjectsAndKeys:(id)firstObject, ...;
 Creation example:
NSDictionary *base = [NSDictionary dictionaryWithObjectsAndKeys:
[NSNumber numberWithInt:2], @“binary”,
[NSNumber numberWithInt:16], @“hexadecimal”, nil];
 Methods
 - (int)count;
 - (id)objectForKey:(id)key;
 - (NSArray *)allKeys;
 - (NSArray *)allValues;

NSMutableDictionary
 Changeable
+ (id)dictionaryWithObjects:(NSArray *)values forKeys:(NSArray *)keys;
+ (id)dictionaryWithObjectsAndKeys:(id)firstObject, ...;
 Creation :
+ (id)dictionary; //creates empty dictionary
 Methods
- (void)setObject:(id)anObject forKey:(id)key;
- (void)removeObjectForKey:(id)key;
- (void)removeAllObjects;
- (void)addEntriesFromDictionary:(NSDictionary *)otherDictionary;
see documentation (apple.com) for more details

NSMutableSet
 Changeable version of NSSet
 Methods
- (void)addObject:(id)anObject; // does nothing if object that isEqual:anObject is already in
- (void)removeObject:(id)anObject;
- (void)unionSet:(NSSet *)otherSet;
- (void)minusSet:(NSSet *)otherSet;
- (void)intersectSet:(NSSet *)otherSet;
see documentation (apple.com) for more details

Other useful Objective-C data
classes
 NSOrderedSet, NSMutableOrderedSet

Cycling through Collections
classes ---- use for-in loop
Example: NSArray of NSString
NSArray *myArray = ...;
for (NSString *string in myArray) { // no way for compiler to know what
// myArray contains
double value = [string doubleValue]; // crash HERE if string not an NSString
}

NSSet example for-in loop
Example: NSSet of id
NSSet *mySet = ...;
for (id obj in mySet) {
// do something with obj, but make sure you
//don’t send it a message it does not respond to
if ([obj isKindOfClass:[NSString class]]) {
// send NSString messages to obj with impunity
}
}

NSDictionary example for-in
loop
Example: NSDictionary
NSDictionary *myDictionary = ...;
for (id key in myDictionary) {
// grab value associated with the current key
id value = [myDictionary objectForKey:key];
// do something with value here ***
}

Property list (plist)
 A collection of collections
 Specifically, it is any graph of objects containing only the following
classes:
○ NSArray, NSDictionary, NSNumber, NSString, NSDate, NSData
 Example1 : NSArray is a Property List if all its members are too --- NSArray
of NSString is a Property List
--- NSArray of NSArray as long as those NSArray’s members are Property
Lists.
 Example 2: NSDictionary is one only if all keys and values are too
 Why define this term?
 Because the SDK has a number of methods which operate on Property Lists.
 Usually to read them from somewhere or write them out to somewhere.
 [plist writeToFile:(NSString *)path atomically:(BOOL)]; // plist is NSArray or
NSDictionary
We will see this in
practice later

NSUserDefaults
 Lightweight storage of Property Lists.
 an NSDictionary that persists between
launches of your application.
 Not a full-on database, so only store
small things like user preferences.

NSUserDefaults continued
 Read and write via a shared instance obtained
via class method standardUserDefaults
[[NSUserDefaults standardUserDefaults] setArray:rvArray forKey:@“RecentlyViewed”];
 Methods (some)
- (void)setDouble:(double)aDouble forKey:(NSString *)key;
- (NSInteger)integerForKey:(NSString *)key; // NSInteger is a typedef to 32 or 64 bit
int
- (void)setObject:(id)obj forKey:(NSString *)key; // obj must be a Property List
- (NSArray *)arrayForKey:(NSString *)key; // will return nil if value for key is not
NSArray
 Always remember to write the defaults out after
each batch of changes!
[[NSUserDefaults standardUserDefaults] synchronize];

CONCLUSION --- a note---Objective-C
2.0 – some features that were added
 In October 2007, Apple Inc. releases
Objective-C 2.0 for Mac OS 10.5
(Leopard)
 Adds automatic garbage collection
(ARC)
 Instance Methods (public functions) are
defined differently using @property
---see next lecture

Objective c intro (1)

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