iOS-创建单例模式

iOS中创建单例模式
方法一:

#pragma mark - 设计单例模式
static id _instance;
//重写allocWithZone:方法
+(instancetype)allocWithZone:(struct _NSZone *)zone{
    @synchronized (self) {
        if (_instance == nil) {
            _instance = [super allocWithZone:zone];
        }
    }
    return _instance;
}
//提供类方法让外界访问唯一的实例
+(instancetype)shareInstance{
    @synchronized (self) {
        if (_instance == nil) {
            _instance = [[self alloc] init];
        }
    }
    return _instance;
}
//实现copyWithZone方法
-(id)copyWithZone:(struct _NSZone *)zone{
    return _instance;
}

方法二:

+(instancetype)sharedInstance {
    static WMSingleton *singleton = nil;
    if (! singleton) {
        singleton = [[self alloc] initPrivate];
    }
    return singleton;
}

- (instancetype)init {
    @throw [NSException exceptionWithName:@"这个是个单例"
                                   reason:@"应该这样调用 [WMSingleton sharedInstance]"
                                 userInfo:nil];
    return nil;
}
//实现自己真正的私有初始化方法
- (instancetype)initPrivate {
    self  = [super init];
    return self;
}

方法三:

static WMObject *_instance;

+ (instancetype)allocWithZone:(struct _NSZone *)zone
{
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        _instance = [super allocWithZone:zone];
    });
    return _instance;
}

+ (instancetype)sharedInstance
{
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        _instance = [[self alloc] init];
    });
    return _instance;
}

- (id)copyWithZone:(NSZone *)zone
{
    return _instance;
}

方法四:

创建一个WMSingleton.h
// .h文件
#define WMSingletonH(name) + (instancetype)shared##name;

// .m文件
#define WMSingletonM(name) \
static id _instance; \
 \
+ (instancetype)allocWithZone:(struct _NSZone *)zone \
{ \
    static dispatch_once_t onceToken; \
    dispatch_once(&onceToken, ^{ \
        _instance = [super allocWithZone:zone]; \
    }); \
    return _instance; \
} \
 \
+ (instancetype)shared##name \
{ \
    static dispatch_once_t onceToken; \
    dispatch_once(&onceToken, ^{ \
        _instance = [[self alloc] init]; \
    }); \
    return _instance; \
} \
 \
- (id)copyWithZone:(NSZone *)zone \
{ \
    return _instance; \
}



使用方法

//.h类
//引入这个宏文件
#import "WMSingleton.h"
@interface WMObject : NSObject
WMSingletonH(object)
@end
//.m类

@implementation WMObject
WMSingletonM(Car)
@end