iOS Session-2

Session - 2

Presented By: A.T.M. Hassan Uzzaman

Agendas

 OOP Concepts in Objective-c
 Delegates and callbacks in Cocoa touch
 Table View, Customizing Cells
 PList (Read, write)

Obj-C vs C#
Obj-C C#
[[object method] method]; obj.method().method();
Memory Pools Garbage Collection
+/- static/instance
nil null
(void)methodWithArg:(int)value {} void method(int value) {}
YES NO true false
@protocol interface

Classes from Apple (and some history)
 NSString is a string of text that is immutable.
 NSMutableString is a string of text that is mutable.
 NSArray is an array of objects that is immutable.
 NSMutableArray is an array of objects that is
mutable.
 NSNumber holds a numeric value.

Objective-C Characteristics and
Symbols
 Written differently from other languages
 Object communicate with messages—does not “call” a
method.
 @ indicates a compiler directive. Objective-C has own
preprocessor that processes @ directives.
 # indicates a preprocessor directive. Processes any #
before it compiles.

Declare in Header file (.h)
Each method will start with either a – or a + symbol.
- indicates an instance method (the receiver is an
instance)
+indicates a class method (the receiver is a class name)
Example of a instance method
-(IBAction)buttonPressed:(id)sender;
Or with one argument
-(void)setFillColor:(NSColor*) newFillColor;

Parts of a Method in a Class
 Implement the method in the .m file
 Example:
-(IBAction)buttonPressed:(id)sender{
do code here….
}
 Example 2:
-(void) setOutlineColor:(NSColor*) outlineColor{
do code here….
}

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

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

Creating class instances
Creating an Object
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

Reference [[Person alloc] init];action
Person *person =
counting in
Retain count begins at 1 with +alloc
[person retain];
Retain count increases to 2 with -retain
[person release];
Retain count decreases to 1 with -release
[person release];
Retain count decreases to 0, -dealloc automatically
called

Autorelease
 Example: returning a newly created object
-(NSString *)fullName
{
NSString *result;
result = [[NSString alloc] initWithFormat:@“%@
%@”, firstName, lastName];

[result autorelease]

return result;
}

Method Names & Autorelease
 Methods whose names includes alloc, copy, or new return a retained
object that the caller needs to release

NSMutableString *string = [[NSMutableString alloc] init];
// We are responsible for calling -release or -autorelease
[string autorelease];

 All other methods return autoreleased objects

NSMutableString *string = [NSMutableString string];
// The method name doesn’t indicate that we need to release
it, so don’t

 This is a convention- follow it in methods you define!

Polymorphism
 Just as the fields of a C structure are in a protected
namespace, so are an object’s instance variables.
 Method names are also protected. Unlike the names of
C functions, method names aren’t global symbols. The
name of a method in one class can’t conflict with
method names in other classes; two very different
classes can implement identically named methods.
 Objective-C implements polymorphism of method
names, but not parameter or operator overloading.

Inheritance

 Class Hierarchies
 Subclass Definitions
 Uses of Inheritance

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;
see documentation (apple.com) for more details

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

We will see this in

Property list (plist) practice later

 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

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.

Use NSError for Most Errors
 No network connectivity
 The remote web service may be inaccessible
 The remote web service may not be able to serve the
information you request
 The data you receive may not match what you were
expecting

Some Methods Pass Errors by
Reference

Exceptions Are Used for
Programmer Errors

Delegates and callbacks in
Cocoa touch

Simple Table App With Diff Image

iOS Session-2

More Related Content

What's hot (20)

Viewers also liked (15)

Similar to iOS Session-2 (20)

Recently uploaded (20)

iOS Session-2