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173 lines
5.1 KiB
Markdown
173 lines
5.1 KiB
Markdown
---
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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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// 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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// 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(.h) file:
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@interface UserObject : NSObject
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{
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// instance variables
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}
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// Class method
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+ (NSString *)classMethod;
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// Instance method
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- (NSString *)instanceMethodWithParmeter:(NSString *)string;
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@end
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// Implement the methods in an implementation (.m) file:
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@implementation UserObject
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+ (NSString *)classMethod
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{
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return @"SomeString";
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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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@end
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// Create an object instance by allocating memory and initializing it. An object is not fully functional until both steps have been completed.
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UserObject *someObject = [[UserObject alloc] init];
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##Calling Methods
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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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[someObject instanceMethodWithParmeter:@"Steve Jobs"];
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##Nested Messages
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// nested messages look like this:
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[someObject instanceMethodWithParmeter:[someObject otherMethodWithString:@"Jony Ive"]];
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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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