Objective-C单例写法

@interface JasonJieSongMapTopDetailsView : UIView

+ (instancetype)shareInstance;
@end
@implementation JasonJieSongMapTopDetailsView

static JasonJieSongMapTopDetailsView* _instance = nil;
+ (instancetype) shareInstance
{
    static dispatch_once_t onceToken ;
    dispatch_once(&onceToken, ^{
        _instance = [[super allocWithZone:NULL] init] ;
    }) ;
    return _instance ;
}

+(id) allocWithZone:(struct _NSZone *)zone
{
    return [JasonJieSongMapTopDetailsView shareInstance] ;
}

-(id) copyWithZone:(struct _NSZone *)zone
{
    return [JasonJieSongMapTopDetailsView shareInstance] ;
}
@end