Reading and writing text files are one of the most basic things you need to do in iPhone development. In iPhone OS 3.0 things have changed a little bit here and there with some methods being deprecated.

I just wrote two example methods that you can use to see how you can turn a NSString into a text file and reverse the process.

Write the Contents of your NSString to the Filesystem

All I needed to do is create a NSString that has five lines in it and then I used the writeToFile method to save the contents. This version of writeToFile is like others that I have wrote about but it has a few more parameters.

//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];

}

Read Something from the Filesystem and Display It

Of course, once you write something to the filesystem you will want to use it again in the future. Here is a method I wrote as an example of this operation.

//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];

}

Discussion

That is it – you can do similar things with content like images and almost anything else with the NSData class. There is also a method in NSString (check out the header files in XCode) which advertises similar functionality for URL so it would look like you can do the same thing with your webserver. I had no luck with this. It was trivial to read a text file from my server, but I could not write files using the methods there; I know this can be done, just not with this very simple approaches.

Tagged as: Cocoa, how to make iphone apps, iPhone Programing, iPhone Programming, Objective-C