iOS6下Objective-C最新特性

WWDC2012釋出了iOS6，同時為Objective C帶來了一些新特性以簡化程式設計。下面是這些新特性，需要XCode4.4及以上版本支援：

1.方法的申明順序不再要求

在方法裡面可以調用在後面申明的方法，編譯器會幫助查找方法的申明，順序不再要求。如下：

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

2.枚舉支援強類型

XCode4.4以前定義枚舉使用如下方式，相當于定義了類型為int的枚舉類型。

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

XCode4.4以後可以為枚舉指明強類型，這樣在指派時會有強類型限制(需要在Build Setting開啟Suspicious implicit conversions)。定義如下：

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

或使用NS_ENUM宏來定義

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

3.預設屬性合成

@interface Person : NSObject @property(strong) NSString *name; @end @implementation Person { NSString *_name;//這句可以省略，XCode很早就可以了 } @synthesize name = _name;//XCode4.4以後，這句也可以省略，XCode預設合成帶下劃線的成員變量 @end

即可以簡化為：

@interface Person : NSObject @property(strong) NSString *name;//ARC開啟，否則需要自己release @end @implementation Person @end

4.建立NSNumber的新文法

XCode4.4以前的建立方式：

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以後可簡化為：

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

XCode4.4以前，使用語句建立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以後可以通過”()”方式建立：

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

5.建立NSArray的新文法

NSArray* array; array = @[ a, b, c ]; //相當于使用下面的方式建立： id objects[] = { a, b, c }; NSUInteger count = sizeof(objects)/ sizeof(id); array = [NSArray arrayWithObjects:objects count:count];

6.建立NSDictionary的新文法

NSDictionary *dict; dict = @{}; dict = @{ k1 : o1 }; dict = @{ k1 : o1, k2 : o2, k3 : o3 }; //相當于如下方式： 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對象的建立，調用對象的-mutableCopy方法

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

8.靜态容器對象的建立，使用+initialize方法

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

9.可變數組新的存取方式：

@implementation SongList { NSMutableArray *_songs; } - (Song *)replaceSong:(Song *)newSong atIndex:(NSUInteger)idx { Song *oldSong = _songs[idx];//使用[idx]通路子對象 _songs[idx] = newSong;//使用[idx]設定子對象 return oldSong; }

10.可變字典新的存取方式：

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