iOS6下Objective-C最新特性

WWDC2012发布了iOS6，同时为Objective C带来了一些新特性以简化编程。下面是这些新特性，需要XCode4.4及以上版本支持：

1.方法的申明顺序不再要求
在方法里面可以调用在后面申明的方法，编译器会帮助查找方法的申明，顺序不再要求。如下：

@interface SongPlayer : NSObject- (void)playSong:(Song *)song;@end@implementation SongPlayer- (void)playSong:(Song *)song {  NSError *error;  [self startAudio:&error];//XCode4.4以前会提示方法未定义，XCode4.4以后可以放心使用  ...}- (void)startAudio:(NSError **)error { ... }@end

2.枚举支持强类型
XCode4.4以前定义枚举使用如下方式，相当于定义了类型为int的枚举类型。

typedef enum {    NSNumberFormatterNoStyle,    NSNumberFormatterDecimalStyle,    NSNumberFormatterCurrencyStyle,    NSNumberFormatterPercentStyle,    NSNumberFormatterScientificStyle,    NSNumberFormatterSpellOutStyle} NSNumberFormatterStyle;// typedef int NSNumberFormatterStyle;

XCode4.4以后可以为枚举指明强类型，这样在赋值时会有强类型限制(需要在Build Setting开启Suspicious implicit conversions)。定义如下：

typedef enum NSNumberFormatterStyle : NSUInteger {    NSNumberFormatterNoStyle,    NSNumberFormatterDecimalStyle,    NSNumberFormatterCurrencyStyle,    NSNumberFormatterPercentStyle,    NSNumberFormatterScientificStyle,    NSNumberFormatterSpellOutStyle} NSNumberFormatterStyle;

或使用NS_ENUM宏来定义

typedef NS_ENUM(NSUInteger, NSNumberFormatterStyle) {    NSNumberFormatterNoStyle,    NSNumberFormatterDecimalStyle,    NSNumberFormatterCurrencyStyle,    NSNumberFormatterPercentStyle,    NSNumberFormatterScientificStyle,    NSNumberFormatterSpellOutStyle};

3.默认属性合成

@interface Person : NSObject@property(strong) NSString *name;@end@implementation Person {    NSString *_name;//这句可以省略，XCode很早就可以了}@synthesize name = _name;//XCode4.4以后，这句也可以省略，XCode默认合成带下划线的成员变量@end

即可以简化为：

@interface Person : NSObject@property(strong) NSString *name;//ARC开启，否则需要自己release@end@implementation Person@end

4.创建NSNumber的新语法
XCode4.4以前的创建方式：

NSNumber *value;value = [NSNumber numberWithChar:'X'];value = [NSNumber numberWithInt:12345];value = [NSNumber numberWithUnsignedLong:12345ul];value = [NSNumber numberWithLongLong:12345ll];value = [NSNumber numberWithFloat:123.45f];value = [NSNumber numberWithDouble:123.45];value = [NSNumber numberWithBool:YES];

XCode4.4以后可简化为：

NSNumber *value;value = @'X';value = @12345;value = @12345ul;value = @12345ll;value = @123.45f;value = @123.45;value = @YES;

XCode4.4以前，使用语句创建NSNumber：

NSNumber *piOverSixteen = [NSNumber numberWithDouble: ( M_PI / 16 )];NSNumber *hexDigit = [NSNumber numberWithChar: "012345679ABCDEF"[i % 16]);NSNumber *usesScreenFonts = [NSNumber numberWithBool:                              [NSLayoutManager usesScreenFonts]];NSNumber *writingDirection = [NSNumber numberWithInt:                                NSWritingDirectionLeftToRight];NSString *path = [NSString stringWithUTF8String: getenv("PATH")];

XCode4.4以后可以通过”()”方式创建：

NSNumber *piOverSixteen = @( M_PI / 16 );NSNumber *hexDigit = @( "012345679ABCDEF"[i % 16] );NSNumber *usesScreenFonts = @( [NSLayoutManager usesScreenFonts] );NSNumber *writingDirection = @( NSWritingDirectionLeftToRight );NSString *path = @( getenv("PATH") );

5.创建NSArray的新语法

NSArray* array;array = @[ a, b, c ];//相当于使用下面的方式创建：id objects[] = { a, b, c };NSUInteger count = sizeof(objects)/ sizeof(id);array = [NSArray arrayWithObjects:objects count:count];

6.创建NSDictionary的新语法

NSDictionary *dict;dict = @{};dict = @{ k1 : o1 };dict = @{ k1 : o1, k2 : o2, k3 : o3 };//相当于如下方式：id objects[] = { o1, o2, o3 };id keys[] = { k1, k2, k3 };NSUInteger count = sizeof(objects) / sizeof(id);dict = [NSDictionary dictionaryWithObjects:objects                                   forKeys:keys                                     count:count];

7.mutable对象的创建，调用对象的-mutableCopy方法

NSMutableArray *mutablePlanets = [@[  @"Mercury", @"Venus", @"Earth",  @"Mars", @"Jupiter", @"Saturn",  @"Uranus", @"Neptune"] mutableCopy];

8.静态容器对象的创建，使用+initialize方法

@implementation MyClassstatic NSArray *thePlanets;+ (void)initialize {  if (self == [MyClass class]) {    thePlanets = @[      @"Mercury", @"Venus", @"Earth",      @"Mars", @"Jupiter", @"Saturn",      @"Uranus", @"Neptune"    ];  }}

9.可变数组新的存取方式：

@implementation SongList {  NSMutableArray *_songs;}- (Song *)replaceSong:(Song *)newSong atIndex:(NSUInteger)idx {    Song *oldSong = _songs[idx];//使用[idx]访问子对象    _songs[idx] = newSong;//使用[idx]设置子对象    return oldSong;}

10.可变字典新的存取方式：

@implementation Database {  NSMutableDictionary *_storage;}- (id)replaceObject:(id)newObject forKey:(id )key {    id oldObject = _storage[key];//相当于id oldObject = [_storage objectForKey:key];    _storage[key] = newObject;//相当于[_storage setObject:object forKey:key];    return oldObject;}