Well Golly

This is a simple method that I use to copy a file from the app bundle to the Documents directory. You can’t modify files in the app bundle, but you can modify them if they are in the Documents directory.

- (void)createResultsDocument {
    
    NSString *documentsDirectory = [self applicationDocumentsDirectory];
    NSString *sourcePath = [[[NSBundle mainBundle] resourcePath] stringByAppendingPathComponent:@"HTML_header.html"];
    
    NSDateFormatter* dateFormatter = [[NSDateFormatter alloc] init];
    [dateFormatter setDateFormat:@"yyyy-MM-dd"];
    NSString *todaysDate = [dateFormatter stringFromDate:[NSDate date]];
    NSString *resultsFileName = [NSString stringWithFormat:@"MPResults_%@.html",todaysDate];
    NSString *destinationPath = [documentsDirectory stringByAppendingPathComponent:resultsFileName];
    NSError *error;
    
    [[NSFileManager defaultManager] copyItemAtPath:sourcePath 
                                            toPath:destinationPath
                                             error:&error];
    NSLog(@"The copy error is: %@", error);
    
    // Check that it worked.
    NSURL *resultsURL = [NSURL fileURLWithPath:destinationPath];
    NSLog(@"The resultsURL is: %@", resultsURL);
}

I created a Utilities singleton to keep things I refer to often. These are the methods I use for referring to directories.

#pragma mark - Application's Documents directory
// Directory locations
+ (NSString *)applicationCachesDirectory {
    return [NSSearchPathForDirectoriesInDomains(NSCachesDirectory, NSUserDomainMask, YES) lastObject];
}

+ (NSString *)applicationDocumentsDirectory {
    return [NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES) lastObject];
}

+ (NSString *)applicationLibraryDirectory {
    
    return [NSSearchPathForDirectoriesInDomains(NSLibraryDirectory, NSUserDomainMask, YES) lastObject];
}

Here’s one for retrieving the contents of a file stored in the Caches Directory. Notice how it uses [self applicationCachesDirectory] to get the location of the directory.

// Cached files for results
+ (NSString *)cachedFilePath:(NSString *)fileName {
    NSString *pathComponent = [NSString stringWithFormat:@"%@.txt",fileName];
    NSString *filePath = [[self applicationCachesDirectory] stringByAppendingPathComponent:pathComponent];
    return filePath;
}

If I want to store the results in the Documents directory, I’ll use this to construct the path.

        NSString *resultsFilePath = [ [Utilities applicationDocumentsDirectory] stringByAppendingPathComponent:[self formattedHTMLFileName:@"Results"] ];

Here’s a slightly more complicated example where I retrieve the contents of a cached file. Note that it makes use of cachedFilePath:fileName as described above.

+ (NSString *)cachedFileContents:(NSString *)fileName {
    NSStringEncoding encoding; NSError* error = nil;
    NSString *text = [NSString stringWithContentsOfFile:[self cachedFilePath:fileName] usedEncoding:&encoding error:&error];
    return text;
}

Here’s another example. This time I’m loading a string with the contents of the FullResults file.

 NSStringEncoding encoding;
    NSError* error = nil;
    NSString *resultsText = [NSString stringWithContentsOfFile:[Utilities cachedFilePath:@"FullResults"] usedEncoding:&encoding error:&error];