--- language: Objective-C contributors: - ["Eugene Yagrushkin", "www.about.me/yagrushkin"] - ["Yannick Loriot", "https://github.com/YannickL"] filename: LearnObjectiveC.m --- 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. It is a general-purpose, object-oriented programming language that adds Smalltalk-style messaging to the C programming language. ```cpp // Single-line comments start with // /* Multi-line comments look like this. */ // Imports the Foundation headers with #import #import #import "MyClass.h" // Your program's entry point is a function called // main with an integer return type. int main (int argc, const char * argv[]) { // Create an autorelease pool to manage the memory into the program NSAutoreleasePool * pool = [[NSAutoreleasePool alloc] init]; // Use NSLog to print lines to the console NSLog(@"Hello World!"); // Print the string "Hello World!" /////////////////////////////////////// // Types & Variables /////////////////////////////////////// // Primitive declarations int myPrimitive1 = 1; long myPrimitive2 = 234554664565; // Object declarations // Put the * in front of the variable names for strongly-typed object declarations MyClass *myObject1 = nil; // Strong typing id myObject2 = nil; // Weak typing // %@ is an object // 'description' is a convention to display the value of the Objects NSLog(@"%@ and %@", myObject1, [myObject2 description]); // Print "(null) and (null)" // String NSString *worldString = @"World"; NSLog(@"Hello %@!", worldString); // prints => "Hello World!" // The mutable version of NSString is NSMutableString that allows to edit // individual characters or append strings together. NSMutableString *mutableString = [NSMutableString stringWithString:@"Hello"]; [mutableString appendString:@" World!"]; NSLog(@"%@", mutableString); // prints => "Hello World!" // Character literals NSNumber *theLetterZNumber = @'Z'; char theLetterZ = [theLetterZNumber charValue]; // or 'Z' NSLog(@"%c", theLetterZ); // Integral literals NSNumber *fortyTwoNumber = @42; int fortyTwo = [fortyTwoNumber intValue]; // or 42 NSLog(@"%i", fortyTwo); NSNumber *fortyTwoUnsignedNumber = @42U; unsigned int fortyTwoUnsigned = [fortyTwoUnsignedNumber unsignedIntValue]; // or 42 NSLog(@"%u", fortyTwoUnsigned); NSNumber *fortyTwoShortNumber = [NSNumber numberWithShort:42]; short fortyTwoShort = [fortyTwoShortNumber shortValue]; // or 42 NSLog(@"%hi", fortyTwoShort); NSNumber *fortyTwoShortNumber = [NSNumber numberWithShort:41]; unsigned short fortyTwoUnsigned = [fortyTwoShortNumber unsignedShortValue]; // or 41 NSLog(@"%hu", fortyTwoUnsigned); NSNumber *fortyTwoLongNumber = @42L; long fortyTwoLong = [fortyTwoLongNumber longValue]; // or 42 NSLog(@"%li", fortyTwoLong); NSNumber *fortyTwoLongNumber = @53L; unsigned long fiftyThreeUnsigned = [fortyTwoLongNumber unsignedLongValue]; // or 53 NSLog(@"%lu", fiftyThreeUnsigned); // Floating point literals NSNumber *piFloatNumber = @3.141592654F; float piFloat = [piFloatNumber floatValue]; // or 3.141592654f NSLog(@"%f", piFloat); // prints => 3.141592654 NSLog(@"%5.2f", piFloat); // prints => " 3.14" NSNumber *piDoubleNumber = @3.1415926535; double piDouble = [piDoubleNumber doubleValue]; // or 3.1415926535 NSLog(@"%f", piDouble); NSLog(@"%4.2f", piDouble); // prints => "3.14" // NSDecimalNumber is Objective-C's fixed-point class more precise then float or double NSDecimalNumber *oneDecNum = [NSDecimalNumber decimalNumberWithString:@"10.99"]; NSDecimalNumber *twoDecNum = [NSDecimalNumber decimalNumberWithString:@"5.002"]; // NSDecimal isn't able to use standard +, -, *, / operators. NSDecimalNumber has its own: [oneDecNum decimalNumberByAdding:twoDecNum]; // add [oneDecNum decimalNumberBySubtracting:twoDecNum]; [oneDecNum decimalNumberByMultiplyingBy:twoDecNum]; [oneDecNum decimalNumberByDividingBy:twoDecNum]; NSLog(@"%@", oneDecNum); // prints => 10.99 as NSDecimalNumber is immutable. // BOOL literals NSNumber *yesNumber = @YES; NSNumber *noNumber = @NO; // or BOOL yesBool = YES; BOOL noBool = NO; NSLog(@"%i", yesBool); // prints => 1 // Array object NSArray *anArray = @[@1, @2, @3, @4]; NSNumber *thirdNumber = anArray[2]; NSLog(@"Third number = %@", thirdNumber); // Print "Third number = 3" // NSMutableArray is mutable version of NSArray allowing to change items in array // and extend or shrink array object. Convenient, but not as efficient as NSArray. NSMutableArray *mutableArray = [NSMutableArray arrayWithCapacity:2]; [mutableArray addObject:@"Hello"]; [mutableArray addObject:@"World"]; [mutableArray removeObjectAtIndex:0]; NSLog(@"%@", [mutableArray objectAtIndex:0]); // prints => "World" // Dictionary object NSDictionary *aDictionary = @{ @"key1" : @"value1", @"key2" : @"value2" }; NSObject *valueObject = aDictionary[@"A Key"]; NSLog(@"Object = %@", valueObject); // Print "Object = (null)" // Set object NSSet *set = [NSSet setWithObjects:@"Hello", @"Hello", @"World", nil]; NSLog(@"%@", set); // prints => {(Hello, World)} /////////////////////////////////////// // Operators /////////////////////////////////////// // The operators works like in the C language // For example: 2 + 5; // => 7 4.2f + 5.1f; // => 9.3f 3 == 2; // => 0 (NO) 3 != 2; // => 1 (YES) 1 && 1; // => 1 (Logical and) 0 || 1; // => 1 (Logical or) ~0x0F; // => 0xF0 (bitwise negation) 0x0F & 0xF0; // => 0x00 (bitwise AND) 0x01 << 1; // => 0x02 (bitwise left shift (by 1)) /////////////////////////////////////// // Control Structures /////////////////////////////////////// // If-Else statement if (NO) { NSLog(@"I am never run"); } else if (0) { NSLog(@"I am also never run"); } else { NSLog(@"I print"); } // Switch statement switch (2) { case 0: { NSLog(@"I am never run"); } break; case 1: { NSLog(@"I am also never run"); } break; default: { NSLog(@"I print"); } break; } // While loops statements int ii = 0; while (ii < 4) { NSLog(@"%d,", ii++); // ii++ increments ii in-place, after using its value. } // => prints "0," // "1," // "2," // "3," // For loops statements int jj; for (jj=0; jj < 4; jj++) { NSLog(@"%d,", jj); } // => prints "0," // "1," // "2," // "3," // Foreach statements NSArray *values = @[@0, @1, @2, @3]; for (NSNumber *value in values) { NSLog(@"%@,", value); } // => prints "0," // "1," // "2," // "3," // Try-Catch-Finally statements @try { // Your statements here @throw [NSException exceptionWithName:@"FileNotFoundException" reason:@"File Not Found on System" userInfo:nil]; } @catch (NSException * e) { NSLog(@"Exception: %@", e); } @finally { NSLog(@"Finally"); } // => prints "Exception: File Not Found on System" // "Finally" /////////////////////////////////////// // Objects /////////////////////////////////////// // Create an object instance by allocating memory and initializing it. // An object is not fully functional until both steps have been completed. MyClass *myObject = [[MyClass alloc] init]; // The Objective-C model of object-oriented programming is based on message // passing to object instances. // In Objective-C one does not simply call a method; one sends a message. [myObject instanceMethodWithParameter:@"Steve Jobs"]; // Clean up the memory you used into your program [pool drain]; // End the program return 0; } /////////////////////////////////////// // Classes And Functions /////////////////////////////////////// // Declare your class in a header(MyClass.h) file: // Class Declaration Syntax: // @interface ClassName : ParentClassName // { // Member variable declarations; // } // -/+ (type) Method declarations; // @end @interface MyClass : NSObject { int count; id data; NSString *name; } // Convenience notation to auto generate public getter and setter @property int count; @property (copy) NSString *name; // Copy the object during assignment. @property (readonly) id data; // Declare only a getter method. // To access public variable in implementation file, use '_' followed by variable name: _count = 5; NSLog(@"%d", _count); // prints => 5 // To access public variable outside implementation file, @property generates setter method // automatically. Method name is 'set' followed by @property variable name: [objInitVar setCount:10]; // objInitVar = variable of object instance @property resides in. NSLog(@"%@", [objInitVar count]); // prints => 10 // Methods +/- (return type)methodSignature:(Parameter Type *)parameterName; // + for class method + (NSString *)classMethod; // - for instance method - (NSString *)instanceMethodWithParameter:(NSString *)string; - (NSNumber *)methodAParameterAsString:(NSString*)string andAParameterAsNumber:(NSNumber *)number; @end // Implement the methods in an implementation (MyClass.m) file: @implementation MyClass // Call when the object is releasing - (void)dealloc { } // Constructors are a way of creating classes // This is a default constructor which is called when the object is creating - (id)init { if ((self = [super init])) { self.count = 1; } return self; } + (NSString *)classMethod { return [[self alloc] init]; } - (NSString *)instanceMethodWithParameter:(NSString *)string { return @"New string"; } - (NSNumber *)methodAParameterAsString:(NSString*)string andAParameterAsNumber:(NSNumber *)number { return @42; } // Methods declared into MyProtocol - (void)myProtocolMethod { // statements } @end /* * A protocol declares methods that can be implemented by any class. * Protocols are not classes themselves. They simply define an interface * that other objects are responsible for implementing. */ @protocol MyProtocol - (void)myProtocolMethod; @end ``` ## Further Reading [Wikipedia Objective-C](http://en.wikipedia.org/wiki/Objective-C) [Learning Objective-C](http://developer.apple.com/library/ios/referencelibrary/GettingStarted/Learning_Objective-C_A_Primer/) [iOS For High School Students: Getting Started](http://www.raywenderlich.com/5600/ios-for-high-school-students-getting-started)