单例的写法

static LocationManager *sharedLocationManager = nil;

/*

+ (LocationManager *)sharedInstance

{

    

    if (!sharedLocationManager) {

        

        sharedLocationManager = [[self allocWithZone:NULL] init];

    }

    

    return sharedLocationManager;

}

*/

// iOS SDK 4.0 之后

+ (LocationManager *)sharedInstance

{

    static LocationManager *sharedLocationManager = nil;

    static dispatch_once_t predicate;

    

    dispatch_once(&predicate, ^{

        

        sharedLocationManager = [[self alloc] init];

        

    });

    

    return sharedLocationManager;

}