File management in iOS

The iPhone provides a comprehensive set of operations for working with files and directories. NSFileManager includes methods for querying the contents of directories, creating, renaming and deleting contents, as well as getting/setting file attributes (readable, writeable, etc).

Point to the Documents Directory

Each application has its own sandbox in which you can read/write files. Files written to the sandbox are persistent across invocations of the application, including across application updates.

You can locate the Documents directory in the sandbox as shown below:

// For error information
NSError *error;
 
// Create file manager
NSFileManager *fileMgr = [NSFileManager defaultManager];
 
// Point to Document directory
NSString *documentsDirectory = [NSHomeDirectory() 
         stringByAppendingPathComponent:@"Documents"];

Creating a File

With the documents directory available, we can now use that path to create a new file in the sandbox and write a few lines of text:

// File we want to create in the documents directory 
// Result is: /Documents/file1.txt
NSString *filePath = [documentsDirectory 
         stringByAppendingPathComponent:@"file1.txt"];
 
// String to write
NSString *str = @"iPhone Developer Tips\nhttp://iPhoneDevelopTips,com";
 
// Write the file
[str writeToFile:filePath atomically:YES 
         encoding:NSUTF8StringEncoding error:&error];
 
// Show contents of Documents directory
NSLog(@"Documents directory: %@",
         [fileMgr contentsOfDirectoryAtPath:documentsDirectory error:&error]);

We build a path to the file we want to create (file1.txt), initialize a string to write into the file, and write out the contents. The last line shows a directory listing of what is in the Documents directory after we create the file, see the figure below:

Renaming a File

To rename a file we move the file to a new path. The code below creates the destination path we are after, requests to move the file, and shows the Documents directory after the move.

// Rename the file, by moving the file
NSString *filePath2 = [documentsDirectory 
                                 stringByAppendingPathComponent:@"file2.txt"];
 
// Attempt the move
if ([fileMgr moveItemAtPath:filePath toPath:filePath2 error:&error] != YES)
  NSLog(@"Unable to move file: %@", [error localizedDescription]);
 
// Show contents of Documents directory
NSLog(@"Documents directory: %@", 
         [fileMgr contentsOfDirectoryAtPath:documentsDirectory error:&error]);

After moving the file, the output should look similar to the image below:

Deleting a File

To round out this tip, let’s look at how to delete a file:

// Attempt to delete the file at filePath2
if ([fileMgr removeItemAtPath:filePath2 error:&error] != YES)
  NSLog(@"Unable to delete file: %@", [error localizedDescription]);
 
// Show contents of Documents directory
NSLog(@"Documents directory: %@",
         [fileMgr contentsOfDirectoryAtPath:documentsDirectory error:&error]);

Once the file is deleted, as expected, the Documents directory is now empty:

These examples touch the surface of working with files. Check out the documentation forNSFileManager for all the specifics.

Source:
http://iphonedevelopertips.com/data-file-management/iphone-file-system-creating-renaming-and-deleting-files.html

Write/Retrieve file to/form document directory

//Method writes a string to a text file
-(void) writeToTextFile{
        //get the documents directory:
        NSArray *paths = NSSearchPathForDirectoriesInDomains
            (NSDocumentDirectory, NSUserDomainMask, YES);
        NSString *documentsDirectory = [paths objectAtIndex:0];

        //make a file name to write the data to using the documents directory:
        NSString *fileName = [NSString stringWithFormat:@"%@/textfile.txt", documentsDirectory];
        //create content - four lines of text
        NSString *content = @"One\nTwo\nThree\nFour\nFive";
        //save content to the documents directory
        [content writeToFile:fileName atomically:NO encoding:NSStringEncodingConversionAllowLossy error:nil];
}

//Method retrieves content from documents directory and
//displays it in an alert
-(void) displayContent{
        //get the documents directory:
        NSArray *paths = NSSearchPathForDirectoriesInDomains
                        (NSDocumentDirectory, NSUserDomainMask, YES);
        NSString *documentsDirectory = [paths objectAtIndex:0];

        //make a file name to write the data to using the documents directory:
        NSString *fileName = [NSString stringWithFormat:@"%@/textfile.txt", documentsDirectory];
        NSString *content = [[NSString alloc] initWithContentsOfFile:fileName usedEncoding:nil error:nil];
        //use simple alert from my library (see previous post for details)
        [ASFunctions alert:content];
        [content release];
}