Objective-C Programming For Dummies Cheat Sheet

Making an Objective-C statement

Programming iPhone and Mac apps in Objective-C is about making a statement. You can recognize a statement in Objective-C immediately by noting the semicolon at the end:

statement;

You will see other lines of code, but unless the line ends with a semicolon, it is not an Objective-C statement.

Objective-C built-in and new data types

The variables you declare in Objective-C, Objective-C data types, must be a type that the compiler can recognize. Objective-C comes with a number of built-in data types, as well as mechanisms to create new ones, for programming your iPhone or Mac OS X applications.

Enumeration types

enum  typeName { identifier1, ... identifiern};

Identifiers are of constants of type int.

typedef

typedef  typeName  identifier;

Associates an identifier with a specific type.

Constants

const type  identifier  = value;
#define identifier value

Allows you to define names for constants.

Objective-C operators

Objective-C operators, like those in other programming languages, let you perform operations on variables (hence the name). Objective-C provides many operators, and keeping track of all of them can be difficult as you program your iPhone or Mac OS X apps.

Use the following tables to jog your memory as to which operator accomplishes what task.

Control statements and loops

In programming, as in life, you have to make decisions and act on them. Objective-C provides control statements and loops to help your program take action. You may want to repeat a set of instructions based on some condition or state, for example, or even change the program execution sequence.

Here is the basic syntax for Objective-C control statements and loops:

if else

if (condition) {
  statement(s) if the condition is true;
  }
else {
  statement(s) if the condition is not true;
  }

for

for (counter; condition; update counter) {
  statement(s) to execute while the condition is true;
  }

for in

for (Type newVariable in expression ) {
  statement(s); 
  }

or

Type existingVariable ;
for (existingVariable in expression) {
  statement(s);
  }

Expression is an object that conforms to the NSFastEnumeration protocol.

• An NSArray and NSSet enumeration is over content.

• An NSDictionary enumeration is over keys.

• An NSManagedObjectModel enumeration is over entities.

while

while (condition) { 
  statement(s) to execute while the condition is true 
  }

do while

do {
  statement(s) to execute while the condition is true 
  } while (condition);

Jump statements

return ;

Stop execution and returns to the calling function.

break;

Leave a loop.

continue;

Skip the rest of the loop and start the next iteration.

goto labelName;
...
labelName:

An absolute jump to another point in the program (don’t use it).

exit();

Terminates your program with an exit code.

Declaring classes and sending messages

Object-oriented programming languages enable you to declare classes, create derived classes (subclass), and send messages to the objects instantiated from a class. This is the essence of object-oriented programming and part of the object-oriented extensions that Objective-C adds to C.

To ensure that everything operates smoothly, compiler directives are available that enable you to inform the compiler of your classes by using @class and #import.

Interface

#import "Superclass.h"
@interface ClassName : Superclass {
instance variable declarations;
}
method declarations
@property(attributes) instance variable declaration;
–d

Implementation

#import "ClassName.h"
@implementation ClassName
@synthesize instance variable ;
method definitions
–d

Message Syntax

[receiver message]

#import

#import “filename.h”

Guarantees that a header file will be included only once.

@class

@class ClassName;

Clues the compiler into user defined types.