iOS6下Objective-C最新特性
編輯：IOS開發綜合
WWDC2012發布了iOS6，同時為Objective C帶來了一些新特性以簡化編程。下面是這些新特性，需要XCode4.4及以上版本支持：
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.枚舉支持強類型
XCode4.4以前定義枚舉使用如下方式，相當於定義了類型為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，這樣在賦值時會有強類型限制(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.默認屬性合成
@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默認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.創建NSNumber的新語法
XCode4.4以前的創建方式：
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，使用語句創建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以後可以通過”()”方式創建：
NSNumber *piOverSixteen = @( M_PI / 16 );
NSNumber *hexDigit = @( "012345679ABCDEF"[i % 16] );
NSNumber *usesScreenFonts = @( [NSLayoutManager usesScreenFonts] );
NSNumber *writingDirection = @( NSWritingDirectionLeftToRight );
NSString *path = @( getenv("PATH") );
5.創建NSArray的新語法
NSArray* array;
array = @[ a, b, c ];
//相當於使用下面的方式創建：
id objects[] = { a, b, c };
NSUInteger count = sizeof(objects)/ sizeof(id);
array = [NSArray arrayWithObjects:objects count:count];
6.創建NSDictionary的新語法
NSDictionary *dict;
dict = @{};
dict = @{ k1 : o1 };
dict = @{ k1 : o1, k2 : o2, k3 : o3 };
//相當於如下方式：
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對象的創建，調用對象的-mutableCopy方法
NSMutableArray *mutablePlanets = [@[
@"Mercury", @"Venus", @"Earth",
@"Mars", @"Jupiter", @"Saturn",
@"Uranus", @"Neptune"
] mutableCopy];
8.靜態容器對象的創建，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]訪問子對象
_songs[idx] = newSong;//使用[idx]設置子對象
return oldSong ;www.2cto.com
}
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];//相當於id oldObject = [_storage objectForKey:key];
_storage[key] = newObject;//相當於[_storage setObject:object forKey:key];
return oldObject;
}
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