宏定義抽取單例

iOS單例設計模式中,我們可以發現,每一個單例的寫法都是相同的,所以我們可以把他們抽取出來,放在一個文件中,當我們要定義一個單例類的時候,就不用再寫重複的代碼了.

下面就教大家用宏定義抽取單例

創建一個.h文件,將相同的代碼用宏定義定義

Singleton.h

// 以後就可以使用interfaceSingleton來替代後面的方法聲明
#define interfaceSingleton(name)  +(instancetype)share##name


#if __has_feature(objc_arc)
// ARC
#define implementationSingleton(name)  \
+ (instancetype)share##name \
{ \
name *instance = [[self alloc] init]; \
return instance; \
} \
static name *_instance = nil; \
+ (instancetype)allocWithZone:(struct _NSZone *)zone \
{ \
static dispatch_once_t onceToken; \
dispatch_once(&onceToken, ^{ \
_instance = [[super allocWithZone:zone] init]; \
}); \
return _instance; \
} \
- (id)copyWithZone:(NSZone *)zone{ \
return _instance; \
} \
- (id)mutableCopyWithZone:(NSZone *)zone \
{ \
return _instance; \
}
#else
// MRC

#define implementationSingleton(name)  \
+ (instancetype)share##name \
{ \
name *instance = [[self alloc] init]; \
return instance; \
} \
static name *_instance = nil; \
+ (instancetype)allocWithZone:(struct _NSZone *)zone \
{ \
static dispatch_once_t onceToken; \
dispatch_once(&onceToken, ^{ \
_instance = [[super allocWithZone:zone] init]; \
}); \
return _instance; \
} \
- (id)copyWithZone:(NSZone *)zone{ \
return _instance; \
} \
- (id)mutableCopyWithZone:(NSZone *)zone \
{ \
return _instance; \
} \
- (oneway void)release \
{ \
} \
- (instancetype)retain \
{ \
return _instance; \
} \
- (NSUInteger)retainCount \
{ \
return  MAXFLOAT; \
}
#endif

上面已經將定義單例類的相同代碼,用宏定義抽取出來了,下面就開始使用了

我們創建一個Tools的單例類

Tools.h

#import <Foundation/Foundation.h>
#import "Singleton.h"

@interface Tools : NSObject<NSCopying, NSMutableCopying>

// share + 當前的類名
//+ (instancetype)shareTools;

interfaceSingleton(Tools);

@end

Tools.m

#import "Tools.h"

@implementation Tools


implementationSingleton(Tools)

@end

以後我們定義單例的時候就可以這麼的簡單創建,代碼是不是簡潔多了,下面我們驗證一下

main.m

#import <Foundation/Foundation.h>
#import "Tools.h"
#import "Person.h"

int main(int argc, const char * argv[]) {

    
    Tools *t1 = [[Tools alloc] init]; //內部會調用allocWithZone
    Tools *t2 = [Tools new];// [[alloc] init]  allocWithZone
    Tools *t3 = [Tools shareTools];
    
    Tools *t4 = [t3 copy];
    Tools *t5 = [t3 mutableCopy];
    
    NSLog(@"%p, %p, %p, %p, %p", t1, t2, t3, t4, t5);
    
    
    // 如何判斷當前是ARC還是MRC?
    // 可以在編譯的時候判斷當前是否是ARC
#if __has_feature(objc_arc)
    NSLog(@"ARC");
#else
    NSLog(@"MRC");
#endif
    return 0;
}

打印結果: