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Diffstat (limited to 'objective-c.html.markdown')
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1 files changed, 183 insertions, 56 deletions
diff --git a/objective-c.html.markdown b/objective-c.html.markdown index 419c0475..453a42a5 100644 --- a/objective-c.html.markdown +++ b/objective-c.html.markdown @@ -4,6 +4,7 @@ language: Objective-C contributors: - ["Eugene Yagrushkin", "www.about.me/yagrushkin"] - ["Yannick Loriot", "https://github.com/YannickL"] + - ["Levi Bostian", "https://github.com/levibostian"] filename: LearnObjectiveC.m --- @@ -11,24 +12,32 @@ 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 +```objective-c // Single-line comments start with // /* -Multi-line comments look like this. +Multi-line comments look like this */ // Imports the Foundation headers with #import +// Use <> to import global files (in general frameworks) +// Use "" to import local files (from project) #import <Foundation/Foundation.h> #import "MyClass.h" +// If you enable modules for iOS >= 7.0 or OS X >= 10.9 projects in +// Xcode 5 you can import frameworks like that: +@import Foundation; + // Your program's entry point is a function called -// main with an integer return type. +// 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]; - + // If using automatic reference counting (ARC), use @autoreleasepool instead: + @autoreleasepool { + // Use NSLog to print lines to the console NSLog(@"Hello World!"); // Print the string "Hello World!" @@ -51,7 +60,7 @@ int main (int argc, const char * argv[]) // String NSString *worldString = @"World"; NSLog(@"Hello %@!", worldString); // prints => "Hello World!" - // NSMutableString is a mutable version of the NSString object. + // NSMutableString is a mutable version of the NSString object NSMutableString *mutableString = [NSMutableString stringWithString:@"Hello"]; [mutableString appendString:@" World!"]; NSLog(@"%@", mutableString); // prints => "Hello World!" @@ -74,16 +83,16 @@ int main (int argc, const char * argv[]) 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 *fortyOneShortNumber = [NSNumber numberWithShort:41]; + unsigned short fortyOneUnsigned = [fortyOneShortNumber unsignedShortValue]; // or 41 + NSLog(@"%u", fortyOneUnsigned); NSNumber *fortyTwoLongNumber = @42L; long fortyTwoLong = [fortyTwoLongNumber longValue]; // or 42 NSLog(@"%li", fortyTwoLong); - NSNumber *fortyTwoLongNumber = @53L; - unsigned long fiftyThreeUnsigned = [fortyTwoLongNumber unsignedLongValue]; // or 53 + NSNumber *fiftyThreeLongNumber = @53L; + unsigned long fiftyThreeUnsigned = [fiftyThreeLongNumber unsignedLongValue]; // or 53 NSLog(@"%lu", fiftyThreeUnsigned); // Floating point literals @@ -105,7 +114,7 @@ int main (int argc, const char * argv[]) [oneDecNum decimalNumberBySubtracting:twoDecNum]; [oneDecNum decimalNumberByMultiplyingBy:twoDecNum]; [oneDecNum decimalNumberByDividingBy:twoDecNum]; - NSLog(@"%@", oneDecNum); // prints => 10.99 as NSDecimalNumber is immutable. + NSLog(@"%@", oneDecNum); // prints => 10.99 as NSDecimalNumber is immutable // BOOL literals NSNumber *yesNumber = @YES; @@ -116,11 +125,12 @@ int main (int argc, const char * argv[]) NSLog(@"%i", yesBool); // prints => 1 // Array object + // May contain different data types, but must be an Objective-C 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. + // and extend or shrink array object. Convenient, but not as efficient as NSArray NSMutableArray *mutableArray = [NSMutableArray arrayWithCapacity:2]; [mutableArray addObject:@"Hello"]; [mutableArray addObject:@"World"]; @@ -131,7 +141,7 @@ int main (int argc, const char * argv[]) NSDictionary *aDictionary = @{ @"key1" : @"value1", @"key2" : @"value2" }; NSObject *valueObject = aDictionary[@"A Key"]; NSLog(@"Object = %@", valueObject); // Print "Object = (null)" - // NSMutableDictionary also available as a mutable dictionary object. + // NSMutableDictionary also available as a mutable dictionary object NSMutableDictionary *mutableDictionary = [NSMutableDictionary dictionaryWithCapacity:2]; [mutableDictionary setObject:@"value1" forKey:@"key1"]; [mutableDictionary setObject:@"value2" forKey:@"key2"]; @@ -140,7 +150,7 @@ int main (int argc, const char * argv[]) // Set object NSSet *set = [NSSet setWithObjects:@"Hello", @"Hello", @"World", nil]; NSLog(@"%@", set); // prints => {(Hello, World)} (may be in different order) - // NSMutableSet also available as a mutable set object. + // NSMutableSet also available as a mutable set object NSMutableSet *mutableSet = [NSMutableSet setWithCapacity:2]; [mutableSet addObject:@"Hello"]; [mutableSet addObject:@"Hello"]; @@ -199,7 +209,7 @@ int main (int argc, const char * argv[]) int ii = 0; while (ii < 4) { - NSLog(@"%d,", ii++); // ii++ increments ii in-place, after using its value. + NSLog(@"%d,", ii++); // ii++ increments ii in-place, after using its value } // => prints "0," // "1," // "2," @@ -225,7 +235,7 @@ int main (int argc, const char * argv[]) // "2," // "3," - // Object for loop statement. Can be used with any Objective-C object type. + // Object for loop statement. Can be used with any Objective-C object type for (id item in values) { NSLog(@"%@,", item); } // => prints "0," @@ -252,17 +262,20 @@ int main (int argc, const char * argv[]) // Objects /////////////////////////////////////// - // Create an object instance by allocating memory and initializing it. - // An object is not fully functional until both steps have been completed. + // 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. + // 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 of @autoreleasepool + } // End the program return 0; @@ -272,79 +285,141 @@ int main (int argc, const char * argv[]) // Classes And Functions /////////////////////////////////////// -// Declare your class in a header(MyClass.h) file: -// Class Declaration Syntax: +// Declare your class in a header file (MyClass.h): +// Class declaration syntax: // @interface ClassName : ParentClassName <ImplementedProtocols> // { -// Member variable declarations; +// type name; <= variable declarations; // } -// -/+ (type) Method declarations; +// @property type name; <= property declarations +// -/+ (type) Method declarations; <= Method declarations // @end -@interface MyClass : NSObject <MyProtocol> +@interface MyClass : NSObject <MyProtocol> // NSObject is Objective-C's base object class. { // Instance variable declarations (can exist in either interface or implementation file) int count; // Protected access by default. - @private id data; // Private access. (More convenient to declare in implementation file) + @private id data; // Private access (More convenient to declare in implementation file) NSString *name; } -// Convenient notation to auto generate public access 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: -MyClass *myClass = [[MyClass alloc] init]; // create MyClass object instance. -[myClass setCount:10]; -NSLog(@"%@", [myClass count]); // prints => 10 +// Convenient notation for public access variables to auto generate a setter method +// By default, setter method name is 'set' followed by @property variable name +@property int propInt; // Setter method name = 'setPropInt' +@property (copy) id copyId; // (copy) => Copy the object during assignment +// (readonly) => Cannot set value outside @interface +@property (readonly) NSString *roString; // Use @synthesize in @implementation to create accessor // You can customize the getter and setter names instead of using default 'set' name: -@property (getter=countGet, setter=countSet:) int count; -[myClass countSet:32]; -NSLog(@"%i", [myClass countGet]); // prints => 32 -// For convenience, you may use dot notation to set object instance variables: -myClass.count = 45; -NSLog(@"%i", myClass.count); // prints => 45 - +@property (getter=lengthGet, setter=lengthSet:) int length; + // Methods +/- (return type)methodSignature:(Parameter Type *)parameterName; -// + for class method +// + for class methods: + (NSString *)classMethod; ++ (MyClass *)myClassFromHeight:(NSNumber *)defaultHeight; -// - for instance method +// - for instance methods: - (NSString *)instanceMethodWithParameter:(NSString *)string; - (NSNumber *)methodAParameterAsString:(NSString*)string andAParameterAsNumber:(NSNumber *)number; -@end +// Constructor methods with arguments: +- (id)initWithDistance:(int)defaultDistance; +// Objective-C method names are very descriptive. Always name methods according to their arguments + +@end // States the end of the interface + + +// To access public variables from the implementation file, @property generates a setter method +// automatically. Method name is 'set' followed by @property variable name: +MyClass *myClass = [[MyClass alloc] init]; // create MyClass object instance +[myClass setCount:10]; +NSLog(@"%d", [myClass count]); // prints => 10 +// Or using the custom getter and setter method defined in @interface: +[myClass lengthSet:32]; +NSLog(@"%i", [myClass lengthGet]); // prints => 32 +// For convenience, you may use dot notation to set and access object instance variables: +myClass.count = 45; +NSLog(@"%i", myClass.count); // prints => 45 + +// Call class methods: +NSString *classMethodString = [MyClass classMethod]; +MyClass *classFromName = [MyClass myClassFromName:@"Hello"]; + +// Call instance methods: +MyClass *myClass = [[MyClass alloc] init]; // Create MyClass object instance +NSString *stringFromInstanceMethod = [myClass instanceMethodWithParameter:@"Hello"]; + +// Selectors +// Way to dynamically represent methods. Used to call methods of a class, pass methods +// through functions to tell other classes they should call it, and to save methods +// as a variable +// SEL is the data type. @selector() returns a selector from method name provided +// methodAParameterAsString:andAParameterAsNumber: is method name for method in MyClass +SEL selectorVar = @selector(methodAParameterAsString:andAParameterAsNumber:); +if ([myClass respondsToSelector:selectorVar]) { // Checks if class contains method + // Must put all method arguments into one object to send to performSelector function + NSArray *arguments = [NSArray arrayWithObjects:@"Hello", @4, nil]; + [myClass performSelector:selectorVar withObject:arguments]; // Calls the method +} else { + // NSStringFromSelector() returns a NSString of the method name of a given selector + NSLog(@"MyClass does not have method: %@", NSStringFromSelector(selectedVar)); +} // Implement the methods in an implementation (MyClass.m) file: @implementation MyClass { - long count; // Private access instance variable. + long distance; // Private access instance variable + NSNumber height; +} + +// To access a public variable from the interface file, use '_' followed by variable name: +_count = 5; // References "int count" from MyClass interface +// Access variables defined in implementation file: +distance = 18; // References "long distance" from MyClass implementation +// To use @property variable in implementation, use @synthesize to create accessor variable: +@synthesize roString = _roString; // _roString available now in @implementation + +// Called before calling any class methods or instantiating any objects ++ (void)initialize +{ + if (self == [MyClass class]) { + distance = 0; + } } -// Call when the object is releasing +// Counterpart to initialize method. Called when an object's reference count is zero - (void)dealloc { + [height release]; // If not using ARC, make sure to release class variable objects + [super dealloc]; // and call parent class dealloc } -// Constructors are a way of creating classes -// This is a default constructor which is called when the object is creating +// Constructors are a way of creating instances of a class +// This is a default constructor which is called when the object is initialized. - (id)init { - if ((self = [super init])) + if ((self = [super init])) // 'super' used to access methods from parent class { - self.count = 1; + self.count = 1; // 'self' used for object to call itself } return self; } +// Can create constructors that contain arguments: +- (id)initWithDistance:(int)defaultDistance +{ + distance = defaultDistance; + return self; +} + (NSString *)classMethod { return [[self alloc] init]; } ++ (MyClass *)myClassFromHeight:(NSNumber *)defaultHeight +{ + height = defaultHeight; + return [[self alloc] init]; +} + - (NSString *)instanceMethodWithParameter:(NSString *)string { return @"New string"; @@ -355,13 +430,19 @@ NSLog(@"%i", myClass.count); // prints => 45 return @42; } +// To create a private method, create the method in the @implementation but not in the @interface +- (NSNumber *)secretPrivateMethod { + return @72; +} +[self secretPrivateMethod]; // Calls private method + // Methods declared into MyProtocol - (void)myProtocolMethod { // statements } -@end +@end // States the end of the implementation /* * A protocol declares methods that can be implemented by any class. @@ -373,12 +454,58 @@ NSLog(@"%i", myClass.count); // prints => 45 @end +/////////////////////////////////////// +// Memory Management +/////////////////////////////////////// +/* +For each object used in an application, memory must be allocated for that object. When the application +is done using that object, memory must be deallocated to ensure application efficiency. +Objective-C does not use garbage collection and instead uses reference counting. As long as +there is at least one reference to an object (also called "owning" an object), then the object +will be available to use (known as "ownership"). + +When an instance owns an object, its reference counter is increments by one. When the +object is released, the reference counter decrements by one. When reference count is zero, +the object is removed from memory. + +With all object interactions, follow the pattern of: +(1) create the object, (2) use the object, (3) then free the object from memory. +*/ + +MyClass *classVar = [MyClass alloc]; // 'alloc' sets classVar's reference count to one. Returns pointer to object +[classVar release]; // Decrements classVar's reference count +// 'retain' claims ownership of existing object instance and increments reference count. Returns pointer to object +MyClass *newVar = [classVar retain]; // If classVar is released, object is still in memory because newVar is owner +[classVar autorelease]; // Removes ownership of object at end of @autoreleasepool block. Returns pointer to object + +// @property can use 'retain' and 'assign' as well for small convenient definitions +@property (retain) MyClass *instance; // Release old value and retain a new one (strong reference) +@property (assign) NSSet *set; // Pointer to new value without retaining/releasing old (weak reference) + +// Automatic Reference Counting (ARC) +// Because memory management can be a pain, Xcode 4.2 and iOS 4 introduced Automatic Reference Counting (ARC). +// ARC is a compiler feature that inserts retain, release, and autorelease automatically for you, so when using ARC, +// you must not use retain, relase, or autorelease +MyClass *arcMyClass = [[MyClass alloc] init]; +// ... code using arcMyClass +// Without ARC, you will need to call: [arcMyClass release] after you're done using arcMyClass. But with ARC, +// there is no need. It will insert this release statement for you + +// As for the 'assign' and 'retain' @property attributes, with ARC you use 'weak' and 'strong' +@property (weak) MyClass *weakVar; // 'weak' does not take ownership of object. If original instance's reference count +// is set to zero, weakVar will automatically receive value of nil to avoid application crashing +@property (strong) MyClass *strongVar; // 'strong' takes ownership of object. Ensures object will stay in memory to use + +// For regular variables (not @property declared variables), use the following: +__strong NSString *strongString; // Default. Variable is retained in memory until it leaves it's scope +__weak NSSet *weakSet; // Weak reference to existing object. When existing object is released, weakSet is set to nil +__unsafe_unretained NSArray *unsafeArray; // Like __weak, but unsafeArray not set to nil when existing object is released ``` ## 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/) +[Programming with Objective-C. Apple PDF book](https://developer.apple.com/library/ios/documentation/cocoa/conceptual/ProgrammingWithObjectiveC/ProgrammingWithObjectiveC.pdf) [iOS For High School Students: Getting Started](http://www.raywenderlich.com/5600/ios-for-high-school-students-getting-started) |