获取系统当前的时间戳(double)
NSDate *date=[NSDate date];
NSTimeInterval spaceTime=date.timeIntervalSince1970;
NSLog(@"%lf",spaceTime); //1449119921.500604
NSDate *date=[NSDate date];
NSTimeInterval spaceTime=date.timeIntervalSince1970;
NSLog(@"%lf",spaceTime); //1449119921.500604