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Diffstat (limited to 'objective-c.html.markdown')
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1 files changed, 319 insertions, 75 deletions
diff --git a/objective-c.html.markdown b/objective-c.html.markdown index f2787649..772e72ca 100644 --- a/objective-c.html.markdown +++ b/objective-c.html.markdown @@ -16,15 +16,21 @@ It is a general-purpose, object-oriented programming language that adds Smalltal // 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 @@ -54,7 +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!" @@ -108,7 +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; @@ -119,12 +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. + // 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"]; @@ -135,7 +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"]; @@ -144,7 +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"]; @@ -203,7 +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," @@ -229,7 +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," @@ -243,32 +249,35 @@ int main (int argc, const char * argv[]) // Your statements here @throw [NSException exceptionWithName:@"FileNotFoundException" reason:@"File Not Found on System" userInfo:nil]; - } @catch (NSException * e) + } @catch (NSException * e) // use: @catch (id exceptionName) to catch all objects. { NSLog(@"Exception: %@", e); } @finally { - NSLog(@"Finally"); + NSLog(@"Finally. Time to clean up."); } // => prints "Exception: File Not Found on System" - // "Finally" + // "Finally. Time to clean up." + + // NSError objects are useful for function arguments to populate on user mistakes. + NSError *error = [NSError errorWithDomain:@"Invalid email." code:4 userInfo:nil]; /////////////////////////////////////// // 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 of @autoreleasepool } // End the program @@ -285,22 +294,22 @@ int main (int argc, const char * argv[]) // { // type name; <= variable declarations; // } -// @property type name; <= property declarations. -// -/+ (type) Method declarations; <= Method declarations. +// @property type name; <= property declarations +// -/+ (type) Method declarations; <= Method declarations // @end @interface MyClass : NSObject <MyProtocol> // NSObject is Objective-C's base object class. { - // Instance variable declarations (can exist in either interface or implementation file). + // 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 for public access variables to auto generate a setter method. -// By default, setter method name is 'set' followed by @property variable name. +// 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. +@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=lengthGet, setter=lengthSet:) int length; @@ -317,14 +326,14 @@ int main (int argc, const char * argv[]) // Constructor methods with arguments: - (id)initWithDistance:(int)defaultDistance; -// Objective-C method names are very descriptive. Always name methods according to their arguments. +// Objective-C method names are very descriptive. Always name methods according to their arguments -@end // States the end of the interface. +@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 *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: @@ -339,39 +348,39 @@ NSString *classMethodString = [MyClass classMethod]; MyClass *classFromName = [MyClass myClassFromName:@"Hello"]; // Call instance methods: -MyClass *myClass = [[MyClass alloc] init]; // Create MyClass object instance. +MyClass *myClass = [[MyClass alloc] init]; // Create MyClass object instance NSString *stringFromInstanceMethod = [myClass instanceMethodWithParameter:@"Hello"]; -// Selectors. +// 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. +// 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. +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. + [myClass performSelector:selectorVar withObject:arguments]; // Calls the method } else { - // NSStringFromSelector() returns a NSString of the method name of a given selector. + // 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 distance; // 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. +_count = 5; // References "int count" from MyClass interface // Access variables defined in implementation file: -distance = 18; // References "long distance" from MyClass implementation. +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. +@synthesize roString = _roString; // _roString available now in @implementation -// Called before calling any class methods or instantiating any objects. +// Called before calling any class methods or instantiating any objects + (void)initialize { if (self == [MyClass class]) { @@ -379,20 +388,20 @@ distance = 18; // References "long distance" from MyClass implementation. } } -// Counterpart to initialize method. Called when an object's reference count is zero. +// 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. + [super dealloc]; // and call parent class dealloc } -// Constructors are a way of creating instances of a class. -// This is a default constructor which is called when the object is initialized. +// 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])) // 'super' used to access methods from parent class. + if ((self = [super init])) // 'super' used to access methods from parent class { - self.count = 1; // 'self' used for object to call itself. + self.count = 1; // 'self' used for object to call itself } return self; } @@ -424,11 +433,12 @@ distance = 18; // References "long distance" from MyClass implementation. return @42; } -// To create a private method, create the method in the @implementation but not in the @interface. +// Objective-C does not have private method declarations, but you can simulate them. +// To simulate a private method, create the method in the @implementation but not in the @interface. - (NSNumber *)secretPrivateMethod { return @72; } -[self secretPrivateMethod]; // Calls private method. +[self secretPrivateMethod]; // Calls private method // Methods declared into MyProtocol - (void)myProtocolMethod @@ -436,19 +446,253 @@ distance = 18; // References "long distance" from MyClass implementation. // statements } -@end // States the end of the implementation. +@end // States the end of the implementation + +/////////////////////////////////////// +// Categories +/////////////////////////////////////// +// A category is a group of methods designed to extend a class. They allow you to add new methods +// to an existing class for organizational purposes. This is not to be mistaken with subclasses. +// Subclasses are meant to CHANGE functionality of an object while categories instead ADD +// functionality to an object. +// Categories allow you to: +// -- Add methods to an existing class for organizational purposes. +// -- Allow you to extend Objective-C object classes (ex: NSString) to add your own methods. +// -- Add ability to create protected and private methods to classes. +// NOTE: Do not override methods of the base class in a category even though you have the ability +// to. Overriding methods may cause compiler errors later between different categories and it +// ruins the purpose of categories to only ADD functionality. Subclass instead to override methods. + +// Here is a simple Car base class. +@interface Car : NSObject + +@property NSString *make; +@property NSString *color; + +- (void)turnOn; +- (void)accelerate; + +@end + +// And the simple Car base class implementation: +#import "Car.h" + +@implementation Car + +@synthesize make = _make; +@synthesize color = _color; + +- (void)turnOn { + NSLog(@"Car is on."); +} +- (void)accelerate { + NSLog(@"Accelerating."); +} + +@end + +// Now, if we wanted to create a Truck object, we would instead create a subclass of Car as it would +// be changing the functionality of the Car to behave like a truck. But lets say we want to just add +// functionality to this existing Car. A good example would be to clean the car. So we would create +// a category to add these cleaning methods: +// @interface filename: Car+Clean.h (BaseClassName+CategoryName.h) +#import "Car.h" // Make sure to import base class to extend. + +@interface Car (Clean) // The category name is inside () following the name of the base class. + +- (void)washWindows; // Names of the new methods we are adding to our Car object. +- (void)wax; + +@end + +// @implementation filename: Car+Clean.m (BaseClassName+CategoryName.m) +#import "Car+Clean.h" // Import the Clean category's @interface file. + +@implementation Car (Clean) + +- (void)washWindows { + NSLog(@"Windows washed."); +} +- (void)wax { + NSLog(@"Waxed."); +} + +@end + +// Any Car object instance has the ability to use a category. All they need to do is import it: +#import "Car+Clean.h" // Import as many different categories as you want to use. +#import "Car.h" // Also need to import base class to use it's original functionality. + +int main (int argc, const char * argv[]) { + @autoreleasepool { + Car *mustang = [[Car alloc] init]; + mustang.color = @"Red"; + mustang.make = @"Ford"; + + [mustang turnOn]; // Use methods from base Car class. + [mustang washWindows]; // Use methods from Car's Clean category. + } + return 0; +} + +// Objective-C does not have protected method declarations but you can simulate them. +// Create a category containing all of the protected methods, then import it ONLY into the +// @implementation file of a class belonging to the Car class: +@interface Car (Protected) // Naming category 'Protected' to remember methods are protected. + +- (void)lockCar; // Methods listed here may only be created by Car objects. + +@end +//To use protected methods, import the category, then implement the methods: +#import "Car+Protected.h" // Remember, import in the @implementation file only. + +@implementation Car + +- (void)lockCar { + NSLog(@"Car locked."); // Instances of Car can't use lockCar because it's not in the @interface. +} + +@end + +/////////////////////////////////////// +// Extensions +/////////////////////////////////////// +// Extensions allow you to override public access property attributes and methods of an @interface. +// @interface filename: Shape.h +@interface Shape : NSObject // Base Shape class extension overrides below. + +@property (readonly) NSNumber *numOfSides; + +- (int)getNumOfSides; + +@end +// You can override numOfSides variable or getNumOfSides method to edit them with an extension: +// @implementation filename: Shape.m +#import "Shape.h" +// Extensions live in the same file as the class @implementation. +@interface Shape () // () after base class name declares an extension. + +@property (copy) NSNumber *numOfSides; // Make numOfSides copy instead of readonly. +-(NSNumber)getNumOfSides; // Make getNumOfSides return a NSNumber instead of an int. +-(void)privateMethod; // You can also create new private methods inside of extensions. + +@end +// The main @implementation: +@implementation Shape + +@synthesize numOfSides = _numOfSides; + +-(NSNumber)getNumOfSides { // All statements inside of extension must be in the @implementation. + return _numOfSides; +} +-(void)privateMethod { + NSLog(@"Private method created by extension. Shape instances cannot call me."); +} + +@end + +/////////////////////////////////////// +// Protocols +/////////////////////////////////////// +// 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 filename: "CarUtilities.h" +@protocol CarUtilities <NSObject> // <NSObject> => Name of another protocol this protocol includes. + @property BOOL engineOn; // Adopting class must @synthesize all defined @properties and + - (void)turnOnEngine; // all defined methods. +@end +// Below is an example class implementing the protocol. +#import "CarUtilities.h" // Import the @protocol file. + +@interface Car : NSObject <CarUtilities> // Name of protocol goes inside <> + // You don't need the @property or method names here for CarUtilities. Only @implementation does. +- (void)turnOnEngineWithUtilities:(id <CarUtilities>)car; // You can use protocols as data too. +@end +// The @implementation needs to implement the @properties and methods for the protocol. +@implementation Car : NSObject <CarUtilities> + +@synthesize engineOn = _engineOn; // Create a @synthesize statement for the engineOn @property. + +- (void)turnOnEngine { // Implement turnOnEngine however you would like. Protocols do not define + _engineOn = YES; // how you implement a method, it just requires that you do implement it. +} +// You may use a protocol as data as you know what methods and variables it has implemented. +- (void)turnOnEngineWithCarUtilities:(id <CarUtilities>)objectOfSomeKind { + [objectOfSomeKind engineOn]; // You have access to object variables + [objectOfSomeKind turnOnEngine]; // and the methods inside. + [objectOfSomeKind engineOn]; // May or may not be YES. Class implements it however it wants. +} + +@end +// Instances of Car now have access to the protocol. +Car *carInstance = [[Car alloc] init]; +[[carInstance setEngineOn:NO]; +[carInstance turnOnEngine]; +if ([carInstance engineOn]) { + NSLog(@"Car engine is on."); // prints => "Car engine is on." +} +// Make sure to check if an object of type 'id' implements a protocol before calling protocol methods: +if ([myClass conformsToProtocol:@protocol(CarUtilities)]) { + NSLog(@"This does not run as the MyClass class does not implement the CarUtilities protocol."); +} else if ([carInstance conformsToProtocol:@protocol(CarUtilities)]) { + NSLog(@"This does run as the Car class implements the CarUtilities protocol."); +} +// Categories may implement protocols as well: @interface Car (CarCategory) <CarUtilities> +// You may implement many protocols: @interface Car : NSObject <CarUtilities, CarCleaning> +// NOTE: If two or more protocols rely on each other, make sure to forward-declare them: +#import "Brother.h" + +@protocol Brother; // Forward-declare statement. Without it, compiler would through error. + +@protocol Sister <NSObject> + +- (void)beNiceToBrother:(id <Brother>)brother; + +@end + +// See the problem is that Sister relies on Brother, and Brother relies on Sister. +#import "Sister.h" + +@protocol Sister; // These lines stop the recursion, resolving the issue. + +@protocol Brother <NSObject> + +- (void)beNiceToSister:(id <Sister>)sister; -/* - * 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 /////////////////////////////////////// +// Blocks +/////////////////////////////////////// +// Blocks are statements of code, just like a function, that are able to be used as data. +// Below is a simple block with an integer argument that returns the argument plus 4. +int (^addUp)(int n); // Declare a variable to store the block. +void (^noParameterBlockVar)(void); // Example variable declaration of block with no arguments. +// Blocks have access to variables in the same scope. But the variables are readonly and the +// value passed to the block is the value of the variable when the block is created. +int outsideVar = 17; // If we edit outsideVar after declaring addUp, outsideVar is STILL 17. +__block long mutableVar = 3; // __block makes variables writable to blocks, unlike outsideVar. +addUp = ^(int n) { // Remove (int n) to have a block that doesn't take in any parameters. + NSLog(@"You may have as many lines in a block as you would like."); + NSSet *blockSet; // Also, you can declare local variables. + mutableVar = 32; // Assigning new value to __block variable. + return n + outsideVar; // Return statements are optional. +} +int addUp = add(10 + 16); // Calls block code with arguments. +// Blocks are often used as arguments to functions to be called later, or for callbacks. +@implementation BlockExample : NSObject + + - (void)runBlock:(void (^)(NSString))block { + NSLog(@"Block argument returns nothing and takes in a NSString object."); + block(@"Argument given to block to execute."); // Calling block. + } + + @end + + +/////////////////////////////////////// // Memory Management /////////////////////////////////////// /* @@ -466,34 +710,34 @@ 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. +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). +// @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. +// 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. +// 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'. +// 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. +// 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. +__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 |