iOS 比较两个时间差

- (NSString *)intervalFromLastDate: (NSString *) dateString1  toTheDate:(NSString *) dateString2

{

    NSArray *timeArray1=[dateString1componentsSeparatedByString:@"."];

    dateString1=[timeArray1 objectAtIndex:0];

    NSArray *timeArray2=[dateString2componentsSeparatedByString:@"."];

    dateString2=[timeArray2 objectAtIndex:0];

    NSLog(@"%@.....%@",dateString1,dateString2);

    NSDateFormatter *date=[[NSDateFormatteralloc] init];

    [date setDateFormat:@"yyyy-MM-dd HH:mm:ss"];

    NSDate *d1=[datedateFromString:dateString1];

    

    NSTimeInterval late1=[d1timeIntervalSince1970]*1;

    NSDate *d2=[datedateFromString:dateString2];

    

    NSTimeInterval late2=[d2timeIntervalSince1970]*1;

    NSTimeInterval cha=late2-late1;

    NSString *timeString=@"";

    NSString *house=@"";

    NSString *min=@"";

    NSString *sen=@"";

    

    sen = [NSStringstringWithFormat:@"%d", (int)cha%60];

    //        min = [min substringToIndex:min.length-7];

    //    秒

    sen=[NSStringstringWithFormat:@"%@", sen];

    min = [NSStringstringWithFormat:@"%d", (int)cha/60%60];

    //        min = [min substringToIndex:min.length-7];

    //    分

    min=[NSStringstringWithFormat:@"%@", min];

    //    小时

    house = [NSStringstringWithFormat:@"%d", (int)cha/3600];

    //        house = [house substringToIndex:house.length-7];

    house=[NSStringstringWithFormat:@"%@", house];

    timeString=[NSStringstringWithFormat:@"%@:%@:%@",house,min,sen];

    

    //    return timeString;

    return [NSStringstringWithFormat:@"%f",cha];

}