how to check file is updated or not without using modified time

how to check file is updated or not without using modified time  in cocoa for mac-osx objective-c

How to get checkSum of a file........

#import "NSData+MD5.h"

@interface NSData(MD5)

 - (NSString *)MD5;

@end

#import <CommonCrypto/CommonDigest.h>

 @implementation NSData(MD5)

- (NSString*)MD5

{

  // Create byte array of unsigned chars

  unsigned char md5Buffer[CC_MD5_DIGEST_LENGTH];

// Create 16 byte MD5 hash value, store in buffer

  CC_MD5(self.bytes, self.length, md5Buffer);

    

// Convert unsigned char buffer to NSString of hex values

  NSMutableString *output = [NSMutableString stringWithCapacity:CC_MD5_DIGEST_LENGTH * 2];

  for(int i = 0; i < CC_MD5_DIGEST_LENGTH; i++) 

[output appendFormat:@"%02x",md5Buffer[i]];

  return output;

}

@end

Call from Own class: 

+(NSString *)getCheckSum:(NSString *)filePath{

     NSData *nsData = [NSData dataWithContentsOfFile:filePath];

     if (nsData){

         return [nsData MD5];

     }

    else{

         return nil;

     }

}

How to check file is open or close objective-c in MAC os-x

How to check file is open or close in cocoa for mac osx (objective -c)

                 NSTask *task = [[NSTask alloc] init];

                    [task setLaunchPath:@"/bin/bash"];

                    [task setArguments:@[ @"-c",  [NSString stringWithFormat:@"lsof %@",FILE_PATH]];

                    [task launch];

                    [task waitUntilExit];

                    int status = [task terminationStatus];

                    if(status==0 ){

                      //file is open

                    }

                    if(status==1){

                       //file is closed  

                        }

                    }

                    task=nil;

Call method after every 1 sec. in Background thread

First time call through:

//call from viewdidload

dispatch_queue_t q_background = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_BACKGROUND, 0);

    dispatch_async(q_background, ^{

        [self checkFileOpenOrNot:nil];

   });

-(void) checkFileOpenOrNot:(id)sender{

//do your code 

dispatch_queue_t q_background = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_BACKGROUND, 0);

            double delayInSeconds = 1.0;

            dispatch_time_t popTime = dispatch_time(DISPATCH_TIME_NOW, delayInSeconds * NSEC_PER_SEC);

            dispatch_after(popTime, q_background, ^(void){

                [self checkFileOpenOrNot:nil];

            });

}