获取时间戳的方法

// 获取时间戳
NSDate* dat = [NSDate dateWithTimeIntervalSinceNow:0];
NSTimeInterval a=[dat timeIntervalSince1970];
NSString *timeString = [NSString stringWithFormat:@"%.0f", a];

- (void)date:(NSString *)timeStampString
{
NSTimeInterval _interval=[timeStampString doubleValue] / 1000.0;
NSDate *date = [NSDate dateWithTimeIntervalSince1970:_interval];
NSDateFormatter *objDateformat = [[NSDateFormatter alloc] init];
[objDateformat setDateFormat:@"yyyy-MM-dd HH:mm:ss.SSS"];
NSLog(@"%@", [objDateformat stringFromDate: date]);
}