转换为时间字符串

+ (NSString *)dateStringFromNumberTimer:(NSString *)timerStr {

  //转化为Double 
  double t = [timerStr doubleValue]; 

  //计算出距离1970的NSDate 
  NSDate *date = [NSDate dateWithTimeIntervalSince1970:t]; 

  //转化为 时间格式化字符串 
  //NSDateFormatter *df = [[[NSDateFormatter alloc] init] autorelease]; 
  NSDateFormatter *df = [[NSDateFormatter alloc] init]; 
  df.dateFormat = @"yyyy-MM-dd HH:mm:ss"; 

  //转化为 时间字符串
  return [df stringFromDate:date];

}```