Session 2 - Objective-C basics

Objective-C Basics
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Session 2
Vu Tran Lam
IAD-2013

• Objective-C introduction
• Creating your ﬁrst Objective-C program
• Variables, data types and pointer
• Basic statements
• Conditions (if, switch)
• Loops (for, while, do... while)
• Primitives array
• Functions
• Exceptions
Today’s Topics

• Objective-C is the native programming language for Apple’s iOS
and OS X operating systems. It’s a compiled, general-purpose
language capable of building everything from command line utilities
to animated GUIs to domain-speciﬁc libraries.
Objective-C Introduction

• Like C++, Objective-C was designed to add object-oriented
features to C, but the two languages accomplished this using
fundamentally distinct philosophies.
• Objective-C is a strict superset of C, which means that it’s possible
to seamlessly combine both languages in the same source ﬁle.
Objective-C Introduction

• Launching Xcode
• Creating “Command Line Tool” project
• Declaring project info
• Run your program
Create Your First Objective-C Program

• Start Xcode and then select Create a New Xcode Project from the
startup screen.
Launching Xcode

• Choose OSX > Application > Command Line Tool project template.
Creating “Command Line Tool” Project

• Input product name, organisation name, company identiﬁer and
type of framework.
Declaring Project Info

• Click on Run button on the tool bar to build and run your program.
Running Your Program

• Comments
• Data types
• Variables
• Operators
• Macros
• Typedef
• Structs
• Enums
• Pointers
Variables, Data Types and Pointer

• There are two ways to include commentary text in a C program.
Inline comments begin with a double slash (//) and terminate at the
end of the current line.
• Block comments can span multiple lines, but they must be
enclosed in /* and */ characters. For example:
// This is an inline comment
/* This is a block comment.
It can span multiple lines. */
Comment

Primitive data types
• void
• char
• (unsigned) short, int, long
• ﬂoat, double
• BOOL (YES, NO, true, false)
Data Types
Reference data types
• NSString
• NSDecimal
• NSNumber
• NSSet
• NSArray
• NSDictionary
• id, Class, SEL

Primitive Data Types
Type Constant Examples NSLog Char
char ‘a’, ‘n’ %c
short int - %hi, %hx, %ho
unsigned short int - %hu, %hx, %ho
int 12, -97, 100U, 0xFFE0 %i, %d, %x
unsigned int 12u, 100U, 0XFFu %u, %x, %o
long int 12L, -2001, 0xfffL %li, %lx, %lo
unsigned long int 12UL, 100u1, 0xffeeUL %lu, %lx, %lo
long long int 0xe5e5e55L, 50011 %lli, %llx, %llo
unsigned long long int 12u11, 0xffeeULL %llu, %llx, %llo
ﬂoat 12.34f, 3.1e-5f, 0x1.5p10, 0x1P-1 %f, %e, %g, %a
double 12.34, 3.1e-5, 0x.1p3 %f, %e, %g, %a
long double 12.34L, 3.1e-51 %lf, $le, %lg
id nil %p

• Variables are containers that can store different values. In C,
variables are statically typed, which means that you must explicitly
state what kind of value they will hold.
• To declare a variable, you use the <type> <name> syntax, and to
assign a value to it you use the = operator.
• If you need to interpret a variable as a different type, you can cast it
by preﬁxing it with the new type in parentheses.
Variables

#import <Foundation/Foundation.h>
!
int main(int argc, const char * argv[])
{
@autoreleasepool
{
char charType = 'A';
double doubleType = 9200.8;
// Casting double value to int value
int intType = (int)doubleType;
id idType = @"Hello World";
NSLog(@"Character value: %c", charType);
NSLog(@"Double value: %.1f", doubleType); // 9200.8
NSLog(@"Integer value: %d", intType); // 9200
NSLog(@"id value: %p", idType);
NSLog(@"id type description: %@", [idType description]);
}
return 0;
}
!
Variables Example

• The const variable modiﬁer can be used to tell the compiler that a
variable is never allowed to change.
• For example, deﬁning a constant called pi and then trying to alter it
will result in a compiler error:
double const pi = 3.14159;
pi = 42001.0; // Compile error
Constants

• Arithmetic operators (+, -, *, %, / )
• Relational operators (==, >, <, >=, <=)
• Logical operators (!, &&, ||)
• Assignment operator (=)
• Conditional operator (?)
Operators

• Macros are a low-level way to deﬁne symbolic constants and
space-saving abbreviations.
• The #deﬁne directive maps a macro name to an expansion, which
is an arbitrary sequence of characters.
• Before the compiler tries to parse the code, the preprocessor
replaces all occurrences of the macro name with its expansion.
Macros

!
// Define macros
#define PI 3.14159
#define RAD_TO_DEG(radians) (radians * (180.0 / PI))
!
{
@autoreleasepool
{
double angle = PI / 2; // 1.570795
NSLog(@"%f", RAD_TO_DEG(angle)); // 90.0
}
return 0;
}
Macros

• The typedef keyword lets you create new data types or redeﬁne existing
ones.
• After typedef’ing an unsigned char in following example, we can use
ColorComponent just like we using char, int, double, or any other built-in
type:
!
typedef unsigned char ColorComponent;
!
{
@autoreleasepool
{
ColorComponent red = 255;
ColorComponent green = 160;
ColorComponent blue = 0;
NSLog(@"Your paint job is (R: %hhu, G: %hhu, B: %hhu)", red, green, blue);
}
return 0;
}
Typedef

• A struct is like a simple, primitive C object. It lets you aggregate several
variables into a more complex data structure, but doesn’t provide any OOP
features (e.g., methods).
• For following example, allow you to create a struct to group the components
of an RGB color.
!
typedef struct
{
unsigned char red;
unsigned char green;
unsigned char blue;
} Color;
!
{
@autoreleasepool
{
Color carColor = {255, 160, 0};
NSLog(@"Your paint job is (R: %hhu, G: %hhu, B: %hhu)", carColor.red,
carColor.green, carColor.blue);
}
return 0;
}
Structs

• The enum keyword is used to create an enumerated type, which is a
collection of related constants.
• Like structs, it’s often convenient to typedef enumerated types with a
descriptive name:
!
typedef struct
{
unsigned char red;
unsigned char green;
unsigned char blue;
} Color;
!
{
@autoreleasepool
{
Color carColor = {255, 160, 0};
NSLog(@"Your paint job is (R: %hhu, G: %hhu, B: %hhu)", carColor.red,
carColor.green, carColor.blue);
}
return 0;
}
Enums

!
typedef enum
{
FORD,
HONDA,
NISSAN,
PORSCHE
} CarModel;
!
{
@autoreleasepool
{
CarModel myCar = NISSAN;
switch (myCar)
{
case FORD:
case PORSCHE:
NSLog(@"You like Western cars?");
break;
case HONDA:
case NISSAN:
NSLog(@"You like Japanese cars?");
break;
default:
break;
}
}
return 0;
}
Enums

• A pointer is a direct reference to a memory address. Whereas a
variable acts as a transparent container for a value, pointers remove
a layer of abstraction and let you see how that value is stored. This
requires two new tools:
• The reference operator (&) returns the memory address of a normal variable.
• The dereference operator (*) returns the contents of a pointer’s memory
address.
// Define a normal variable
int year = 1967;
// Declare a pointer that points to an int
int *pointer;
// Find the memory address of the variable
pointer = &year;
// Dereference the address to get its value
NSLog(@"%d", *pointer);
// Assign a new value to the memory address
*pointer = 1990;
NSLog(@"%d", year);
Pointers

• The null pointer is a special kind of pointer that doesn’t point to
anything. There is only one null pointer in C, and it is referenced
through the NULL macro.
• This is useful for indicating empty variables something that is not
possible with a normal data type. For instance, the following snippet
shows how pointer can be “emptied” using the null pointer.
int year = 1967;
int *pointer = &year;
NSLog(@"%d", *pointer); // Do something with the value
pointer = NULL; // Then invalidate it
Null Pointers

• A void pointer is a generic type that can point to anything. It’s
essentially a reference to an arbitrary memory address.
• Accordingly, more information is required to interpret the contents of
a void pointer. The easiest way to do this is to simply cast it to a
non-void pointer.
• For example, the (int *) statement in the following code interprets the
contents of the void pointer as an int value.
int year = 1967;
void *genericPointer = &year;
int *intPointer = (int *)genericPointer;
NSLog(@"%d", *intPointer);
Void Pointers

• This is all good background knowledge, but for your Objective-C
development, you probably won’t need to use most of it.
• The only thing that you really have to understand is that all
Objective-C objects are referenced as pointers.
• For instance, an NSString object must be stored as a pointer, not a
normal variable:
NSString *anObject; // An Objective-C object
anObject = NULL; // This will work
anObject = nil; // But this is preferred
int *aPointer; // A plain old C pointer
aPointer = nil; // Don't do this
aPointer = NULL; // Do this instead
Pointers in Objective-C

• Basic statements
• Conditions (if, switch)
• Loops (for, while, do... while)
Basic Statements

• if statement
• switch statement
Conditional Statements

int modelYear = 1990;
if (modelYear < 1967)
{
NSLog(@"That car is an antique!!!");
}
else if (modelYear <= 1991)
{
NSLog(@"That car is a classic!");
}
else if (modelYear == 2013)
{
NSLog(@"That's a brand new car!");
}
else
{
NSLog(@"There's nothing special about that car.");
}
if Statement

// Switch statements (only work with integral types)
switch (modelYear)
{
case 1987:
NSLog(@"Your car is from 1987.");
break;
case 1988:
NSLog(@"Your car is from 1988.");
break;
case 1989:
case 1990:
NSLog(@"Your car is from 1989 or 1990.");
break;
default:
NSLog(@"I have no idea when your car was made.");
break;
}
switch Statement

• for
• while
• do..while
Loop Statements

int modelYear = 1990;
// While loop
int i = 0;
while (i<5)
{
if (i == 3)
{
NSLog(@"Aborting the while-loop");
break;
}
NSLog(@"Current year: %d", modelYear + i);
i++;
}
// For loop
for (int i=0; i<5; i++)
{
if (i == 3)
{
NSLog(@"Skipping a for-loop iteration");
continue;
}
NSLog(@"Current year: %d", modelYear + i);
}
Loops Statements

• Since Objective-C is a superset of C, it has access to the primitive arrays
found in C.
• Generally, the higher-level NSArray and NSMutableArray classes provided by
the Foundation Framework are much more convenient than C arrays;
however, primitive arrays can still prove useful for performance intensive
environments.
• Their syntax is as follows:
!
{
@autoreleasepool
{
int years[4] = {1968, 1970, 1989, 1999};
years[0] = 1967;
for (int i = 0; i < 4; i++)
{
NSLog(@"The year at index %d is: %d", i, years[i]);
}
}
return 0;
}
Primitives Arrays

• Along with variables, conditionals, and loops, functions are one of
the fundamental components of any modern programming
language.
• They let you reuse an arbitrary block of code throughout your
application, which is necessary for organizing and maintaining all
but the most trivial code bases.
• Type of functions:
• Build-in functions (NSLog, NSMakeRange, CFCreateImage,…)
• User-deﬁned functions
User-deﬁned Functions

• Exceptions are represented by the NSException class. It’s designed
to be a universal way to encapsulate exception data, so you should
rarely need to subclass it or otherwise deﬁne a custom exception
object. NSException’s three main properties are listed below
Exceptions & Errors
Property Description
name An NSString that uniquely identiﬁes the exception.
reason
An NSString that contains a human-readable
description of the exception.
userInfo
An NSDictionary whose key-value pairs contain extra
information about the exception. This varies based on
the type of exception.-

• Exceptions can be handled using the standard try-catch-finally
pattern found in most other high-level programming languages.
First, you need to place any code that might result in an exception
in an @try block. Then, if an exception is thrown, the corresponding
@catch() block is executed to handle the problem. The @finally
block is called afterwards, regardless of whether or not an
exception occurred.
• The following main.m file raises an exception by trying to access an
array element that doesn’t exist. In the @catch() block, we simply
display the exception details. The NSException *theException in the
parentheses defines the name of the variable containing the
exception object.
Handling Exceptions

!
{
@autoreleasepool
{
NSArray *inventory = @[@"Honda Civic",
@"Nissan Versa",
@"Ford F-150"];
int selectedIndex = 3;
@try
{
NSString *car = inventory[selectedIndex];
NSLog(@"The selected car is: %@", car);
}
@catch(NSException *theException)
{
NSLog(@"An exception occurred: %@", theException.name);
NSLog(@"Here are some details: %@", theException.reason);
}
@finally
{
NSLog(@"Executing finally block");
}
}
return 0;
}
Handling Exceptions

• Cocoa predefines a number of generic exception names to identify
exceptions that you can handle in your own code. The generic
exception names are string constants defined in NSException.h
• NSGenericException
• NSRangeException
• NSInvalidArgumentException
• NSInternalInconsistencyException
• NSObjectInaccessibleException, NSObjectNotAvailableException
• NSDestinationInvalidException
• NSPortTimeoutException
• NSInvalidSendPortException, NSInvalidReceivePortException
• NSPortSendException, NSPortReceiveException
Predefined Exceptions

Documentation
Programming with Objective-C
https://developer.apple.com/library/ios/documentation/Cocoa/Conceptual/ProgrammingWithObjectiveC/
Introduction/Introduction.html
Exception Programming Topics
https://developer.apple.com/library/mac/documentation/Cocoa/Conceptual/Exceptions/Concepts/
PredeﬁnedExceptions.html

many thanks
to
lamvt@fpt.com.vn
please
say
Stanford University
https://developer.apple.com
Developer Center
http://www.stanford.edu/class/cs193p
xin
chào

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Objective-C - Part 1

Session 2 - Objective-C basics

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