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diff --git a/objective-c.html (levi-dell-banno-laptop's conflicted copy 2014-01-07).markdown b/objective-c.html (levi-dell-banno-laptop's conflicted copy 2014-01-07).markdown new file mode 100644 index 00000000..490fefee --- /dev/null +++ b/objective-c.html (levi-dell-banno-laptop's conflicted copy 2014-01-07).markdown @@ -0,0 +1,446 @@ +--- + +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 <Foundation/Foundation.h> +#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]; + // 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!" + + /////////////////////////////////////// + // 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!" + // NSMutableString is a mutable version of the NSString object. + 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 a fixed-point class that's more precise then float or double + NSDecimalNumber *oneDecNum = [NSDecimalNumber decimalNumberWithString:@"10.99"]; + NSDecimalNumber *twoDecNum = [NSDecimalNumber decimalNumberWithString:@"5.002"]; + // NSDecimalNumber isn't able to use standard +, -, *, / operators so it provides its own: + [oneDecNum decimalNumberByAdding:twoDecNum]; + [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)" + // NSMutableDictionary also available as a mutable dictionary object. + NSMutableDictionary *mutableDictionary = [NSMutableDictionary dictionaryWithCapacity:2]; + [mutableDictionary setObject:@"value1" forKey:@"key1"]; + [mutableDictionary setObject:@"value2" forKey:@"key2"]; + [mutableDictionary removeObjectForKey:@"key1"]; + + // 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 *mutableSet = [NSMutableSet setWithCapacity:2]; + [mutableSet addObject:@"Hello"]; + [mutableSet addObject:@"Hello"]; + NSLog(@"%@", mutableSet); // prints => {(Hello)} + + // 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," + + // Object for loop statement. Can be used with any Objective-C object type. + for (id item in values) { + NSLog(@"%@,", item); + } // => 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 of @autoreleasepool. + } + + // End the program + return 0; +} + +/////////////////////////////////////// +// Classes And Functions +/////////////////////////////////////// + +// Declare your class in a header file (MyClass.h): +// Class declaration syntax: +// @interface ClassName : ParentClassName <ImplementedProtocols> +// { +// type name; <= variable 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). + int count; // Protected access by default. + @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. +@property int count; // Setter name = 'setCount' +@property (copy) NSString *name; // (copy) => Copy the object during assignment. +@property (readonly) id data; // (readonly) => Declare only a getter method. +// You can customize the getter and setter names instead of using default 'set' name: +@property (getter=lengthGet, setter=lengthSet:) int length; + +// 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 // 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(@"%@", [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 + + +// Implement the methods in an implementation (MyClass.m) file: +@implementation MyClass { + long distance; // Private access instance variable. +} + +// To access public variable from the interface file, use '_' followed by variable name: +_count = 5; // References "int count" from MyClass interface. +NSLog(@"%d", _count); // prints => 5 +// Access variables defined in implementation file: +distance = 18; // References "long distance" from MyClass implementation. +NSLog(@"%li", distance); // prints => 18 + +// 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 // States the end of the implementation. + +/* + * 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 + + +/////////////////////////////////////// +// 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 or 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). + +// 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]; // 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) + +[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) diff --git a/objective-c.html.markdown b/objective-c.html.markdown index 406b2e92..a70351b5 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 --- @@ -28,7 +29,9 @@ 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!" @@ -74,16 +77,16 @@ 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 @@ -116,6 +119,7 @@ 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" @@ -146,10 +150,6 @@ int main (int argc, const char * argv[]) [mutableSet addObject:@"Hello"]; NSLog(@"%@", mutableSet); // prints => {(Hello)} - // Set object - NSSet *set = [NSSet setWithObjects:@"Hello", @"Hello", @"World", nil]; - NSLog(@"%@", set); // prints => {(Hello, World)} - /////////////////////////////////////// // Operators /////////////////////////////////////// @@ -267,6 +267,9 @@ int main (int argc, const char * argv[]) // Clean up the memory you used into your program [pool drain]; + + // End of @autoreleasepool. + } // End the program return 0; @@ -276,41 +279,30 @@ 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) + // 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 count; // Setter method name = 'setCount' +@property (copy) NSString *name; // (copy) => Copy the object during assignment. +@property (readonly) id data; // (readonly) => Cannot set value outside interface. // 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; @@ -321,20 +313,39 @@ NSLog(@"%i", myClass.count); // prints => 45 - (NSString *)instanceMethodWithParameter:(NSString *)string; - (NSNumber *)methodAParameterAsString:(NSString*)string andAParameterAsNumber:(NSNumber *)number; -@end +@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 + // Implement the methods in an implementation (MyClass.m) file: @implementation MyClass { - long count; // Private access instance variable. + long distance; // Private access instance variable. } +// 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. + // 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 +// This is a default constructor which is called when the object is initialized. - (id)init { if ((self = [super init])) @@ -365,7 +376,7 @@ NSLog(@"%i", myClass.count); // prints => 45 // statements } -@end +@end // States the end of the implementation. /* * A protocol declares methods that can be implemented by any class. @@ -395,37 +406,40 @@ 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. +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. +// '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 or assign as well for small convenient definitions. +// @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]; // 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. +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 +// 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. +@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. +__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) |