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Merge pull request #490 from YannickL/master

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Minor changes for the objective-c file
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Adam Bard 2014-01-23 08:39:44 -08:00
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@ -12,19 +12,25 @@ 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
@ -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,"
@ -256,19 +262,19 @@ 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 of @autoreleasepool
}
// End the program
@ -285,22 +291,22 @@ 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 +323,14 @@ 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 +345,39 @@ 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 +385,20 @@ 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 +430,11 @@ 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.
// 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.
[self secretPrivateMethod]; // Calls private method
// Methods declared into MyProtocol
- (void)myProtocolMethod
@ -436,7 +442,7 @@ distance = 18; // References "long distance" from MyClass implementation.
// statements
}
@end // States the end of the implementation.
@end // States the end of the implementation
/*
* A protocol declares methods that can be implemented by any class.
@ -466,34 +472,34 @@ 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