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objective-c.html.markdown
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---
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language: Objective-C
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contributors:
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- ["Eugene Yagrushkin", "www.about.me/yagrushkin"]
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- ["Yannick Loriot", "https://github.com/YannickL"]
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filename: LearnObjectiveC.m
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---
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Objective-C is the main programming language used by Apple for the OS X and iOS operating systems and their respective frameworks, Cocoa and Cocoa Touch.
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It is a general-purpose, object-oriented programming language that adds Smalltalk-style messaging to the C programming language.
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```Objective-C
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// Single-line comments start with //
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/*
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Multi-line comments look like this.
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*/
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// Imports the Foundation headers with #import
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#import <Foundation/Foundation.h>
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#import "MyClass.h"
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// Your program's entry point is a function called
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// main with an integer return type.
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int main (int argc, const char * argv[])
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{
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// Create an autorelease pool to manage the memory into the program
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NSAutoreleasePool * pool = [[NSAutoreleasePool alloc] init];
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// Use NSLog to print lines to the console
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NSLog(@"Hello World!"); // Print the string "Hello World!"
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///////////////////////////////////////
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// Types & Variables
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///////////////////////////////////////
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// Primitive declarations
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int myPrimitive1 = 1;
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long myPrimitive2 = 234554664565;
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// Object declarations
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// Put the * in front of the variable names for strongly-typed object declarations
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MyClass *myObject1 = nil; // Strong typing
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id myObject2 = nil; // Weak typing
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// %@ is an object
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// 'description' is a convention to display the value of the Objects
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NSLog(@"%@ and %@", myObject1, [myObject2 description]); // Print "(null) and (null)"
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// String
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NSString *worldString = @"World";
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NSLog(@"Hello %@!", worldString); // Print "Hello World!"
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// Character literals
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NSNumber *theLetterZNumber = @'Z';
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char theLetterZ = [theLetterZNumber charValue];
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NSLog(@"%c", theLetterZ);
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// Integral literals
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NSNumber *fortyTwoNumber = @42;
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int fortyTwo = [fortyTwoNumber intValue];
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NSLog(@"%i", fortyTwo);
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NSNumber *fortyTwoUnsignedNumber = @42U;
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unsigned int fortyTwoUnsigned = [fortyTwoUnsignedNumber unsignedIntValue];
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NSLog(@"%u", fortyTwoUnsigned);
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NSNumber *fortyTwoShortNumber = [NSNumber numberWithShort:42];
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short fortyTwoShort = [fortyTwoShortNumber shortValue];
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NSLog(@"%hi", fortyTwoShort);
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NSNumber *fortyTwoLongNumber = @42L;
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long fortyTwoLong = [fortyTwoLongNumber longValue];
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NSLog(@"%li", fortyTwoLong);
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// Floating point literals
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NSNumber *piFloatNumber = @3.141592654F;
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float piFloat = [piFloatNumber floatValue];
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NSLog(@"%f", piFloat);
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NSNumber *piDoubleNumber = @3.1415926535;
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piDouble = [piDoubleNumber doubleValue];
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NSLog(@"%f", piDouble);
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// BOOL literals
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NSNumber *yesNumber = @YES;
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NSNumber *noNumber = @NO;
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// Array object
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NSArray *anArray = @[@1, @2, @3, @4];
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NSNumber *thirdNumber = anArray[2];
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NSLog(@"Third number = %@", thirdObject); // Print "Third number = 3"
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// Dictionary object
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NSDictionary *aDictionary = @{ @"key1" : @"value1", @"key2" : @"value2" };
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NSObject *valueObject = aDictionary[@"A Key"];
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NSLog(@"Object = %@", valueObject); // Print "Object = (null)"
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///////////////////////////////////////
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// Operators
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///////////////////////////////////////
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// The operators works like in the C language
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// For example:
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2 + 5; // => 7
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4.2f + 5.1f; // => 9.3f
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3 == 2; // => 0 (NO)
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3 != 2; // => 1 (YES)
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1 && 1; // => 1 (Logical and)
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0 || 1; // => 1 (Logical or)
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~0x0F; // => 0xF0 (bitwise negation)
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0x0F & 0xF0; // => 0x00 (bitwise AND)
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0x01 << 1; // => 0x02 (bitwise left shift (by 1))
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///////////////////////////////////////
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// Control Structures
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///////////////////////////////////////
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// If-Else statement
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if (NO)
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{
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NSLog(@"I am never run");
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} else if (0)
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{
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NSLog(@"I am also never run");
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} else
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{
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NSLog(@"I print");
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}
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// Switch statement
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switch (2)
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{
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case 0:
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{
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NSLog(@"I am never run");
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} break;
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case 1:
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{
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NSLog(@"I am also never run");
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} break;
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default:
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{
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NSLog(@"I print");
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} break;
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}
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// While loops statements
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int ii = 0;
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while (ii < 4)
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{
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NSLog(@"%d,", ii++); // ii++ increments ii in-place, after using its value.
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} // => prints "0,"
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// "1,"
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// "2,"
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// "3,"
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// For loops statements
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int jj;
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for (jj=0; jj < 4; jj++)
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{
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NSLog(@"%d,", ii++);
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} // => prints "0,"
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// "1,"
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// "2,"
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// "3,"
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// Foreach statements
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NSArray *values = @[@0, @1, @2, @3];
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for (NSNumber *value in values)
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{
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NSLog(@"%@,", value);
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} // => prints "0,"
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// "1,"
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// "2,"
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// "3,"
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// Try-Catch-Finally statements
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@try
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{
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// Your statements here
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@throw [NSException exceptionWithName:@"FileNotFoundException" reason:@"File Not Found on System" userInfo:nil];
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} @catch (NSException * e)
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{
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NSLog(@"Exception: %@", e);
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} @finally
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{
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NSLog(@"Finally");
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} // => prints "Exception: File Not Found on System"
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// "Finally"
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///////////////////////////////////////
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// Objects
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///////////////////////////////////////
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// Create an object instance by allocating memory and initializing it.
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// An object is not fully functional until both steps have been completed.
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MyClass *myObject = [[MyClass alloc] init];
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// The Objective-C model of object-oriented programming is based on message passing to object instances.
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// In Objective-C one does not simply call a method; one sends a message.
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[myObject instanceMethodWithParmeter:@"Steve Jobs"];
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// Clean up the memory you used into your program
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[pool drain];
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// End the program
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return 0;
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}
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///////////////////////////////////////
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// Classes And Functions
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///////////////////////////////////////
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// Declare your class in a header(MyClass.h) file:
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// Class Declaration Syntax:
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// @interface ClassName : ParentClassName <ImplementedProtocols>
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// {
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// Member variable declarations;
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// }
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// -/+ (type) Method declarations;
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// @end
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@interface MyClass : NSObject <MyCustomProtocol>
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{
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int count;
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id data;
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NSString *name;
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}
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// Convenience notation to auto generate public getter and setter
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@property int count;
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@property (copy) NSString *name; // Copy the object during assignment.
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@property (readonly) id data; // Declare only a getter method.
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// Methods
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+/- (return type)methodSignature:(Parameter Type *)parameterName;
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// + for class method
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+ (NSString *)classMethod;
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// - for instance method
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- (NSString *)instanceMethodWithParmeter:(NSString *)string;
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- (NSNumber *)methodAParameterAsString:(NSString*)string andAParameterAsNumber:(NSNumber *)number;
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-
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@end
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// Implement the methods in an implementation (MyClass.m) file:
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@implementation UserObject
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// Call when the object is releasing
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- (void)dealloc
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{
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}
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// Constructors are a way of creating classes
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// This is a default constructor which is call when the object is creating
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- (id)init
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{
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if ((self = [super init]))
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{
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self.count = 1;
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}
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return self;
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}
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+ (NSString *)classMethod
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{
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return [[self alloc] init];
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}
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- (NSString *)instanceMethodWithParmeter:(NSString *)string
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{
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return @"New string";
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}
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- (NSNumber *)methodAParameterAsString:(NSString*)string andAParameterAsNumber:(NSNumber *)number
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{
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return @42;
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}
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// Methods declared into MyProtocol
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- (void)myProtocolMethod
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{
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// statements
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}
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@end
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/*
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* A protocol declares methods that can be implemented by any class.
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* Protocols are not classes themselves. They simply define an interface
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* that other objects are responsible for implementing.
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* /
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@protocol MyProtocol
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- (void)myProtocolMethod;
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@end
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```
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## Further Reading
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[Wikipedia Objective-C](http://en.wikipedia.org/wiki/Objective-C)
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[Learning Objective-C](http://developer.apple.com/library/ios/referencelibrary/GettingStarted/Learning_Objective-C_A_Primer/)
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[iOS For High School Students: Getting Started](http://www.raywenderlich.com/5600/ios-for-high-school-students-getting-started)
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