What is the best practices for sharing methods across classes in an app?

Question

I'm still trying to wrap my head around how things should be done in the object-oriented world and I think my problem is that I don't understand how to best utilize encapsulation. Specifically, I have lots of small bits of code that I use in several classes in my project. For example:

+ (NSString *)getFormattedDate;
+ (NSString *)getResultsFilePath;
+ (NSError *)removeFileFromCache:(NSString *)fileName;

These are all 3-5 line methods that I use in more than one class. My standard practice has been to put these snippets into a Utility.inc file and call them when I need them. Is that appropriate in the object-oriented world or should each class be self-contained? And if it's appropriate, would you put the code into a singleton or just a regular class file and [[Utilities alloc] init] in each class where you want to use the methods?

Answer 1

Thanks for the answers. I'm not sure that this the right way to do things, but this is what I've done on the projects I just submitted.

I made two classes, one for Utility methods and one for globals. The methods in the Utilities class are all class methods since they operate on files and constants or globals. Then I made a singleton for global variables. I have all of my global constants in the .pch file. Also in the .pch file I put the following two lines of code so that the utilities and globals are available everywhere.

 // File for utilities like file delete, find Documents file
    #import "Utilities.h" 
    #import "Globals.h"

Accessing the methods is straightforward. Here's an example of a call to both methods to generate an HTML header for an email.

NSString *gameNameHeader = [NSString stringWithFormat:@"<p>&nbsp</p><h1>%@ Results</h1><h2>%@%@</h2>",GAME_NAME_TITLE,[Utilities formattedClientName], [Utilities formattedDate]];

In case anyone can use it, here is my current version of the code. (Sorry for the formatting-I can't seem to get the wiki to cooperate.)

@interface Utilities : NSObject {


}

+ (NSString *)formattedDate;
+ (NSString *)formattedClientName;

+ (NSString *)cachedResultsFilePath;
+ (NSString *)cachedResultsFileContents;
+ (NSString *)resultsFileName;
+ (NSError *)removeFileFromCache:(NSString *)fileName;

+ (NSString *)applicationCachesDirectory;
+ (NSString *)applicationDocumentsDirectory;
+ (NSString *)applicationLibraryDirectory;

+ (NSError *)copyCachedResultsToFile;
@end



    #import "Utilities.h"
@implementation Utilities {

    }

+ (NSString *)formattedDate {
    NSDateFormatter* dateFormatter = [[NSDateFormatter alloc] init];
    [dateFormatter setDateFormat:@"yyyy-MM-dd"];
    NSString *todaysDate = [dateFormatter stringFromDate:[NSDate date]];
    return todaysDate;
}

+ (NSString *)formattedClientName {
    NSString *client = [NSString stringWithFormat:@" "]; 
    if( [Globals sharedInstance].currentClient ) client = [NSString stringWithFormat:@" %@ ",[Globals sharedInstance].currentClient];
    return client;
}

+ (NSString *)cachedResultsFilePath {
    NSString *resultsFilePath = [[self applicationCachesDirectory] stringByAppendingPathComponent:@"Results.txt"];
    return resultsFilePath;
}

+ (NSString *)cachedResultsFileContents {
    NSStringEncoding encoding; NSError* error = nil;
    NSString *resultsText = [NSString stringWithContentsOfFile:[self cachedResultsFilePath] usedEncoding:&encoding error:&error];
    return resultsText;
}

+ (NSString *)resultsFileName {
    return [NSString stringWithFormat:@"%@ Results%@%@.html",GAME_NAME_TITLE,[self formattedClientName],[self formattedDate] ];

}

+ (NSError *)removeFileFromCache:(NSString *)fileName {
    NSError *error = nil;
    NSFileManager *localFileManager=[[NSFileManager alloc] init];
    NSString *fullPath = [NSString stringWithFormat:@"%@/%@", [self applicationCachesDirectory],fileName];
    [localFileManager removeItemAtPath: fullPath error:&error ];
    return error;
}

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

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

+ (NSString *)applicationLibraryDirectory {

    return [NSSearchPathForDirectoriesInDomains(NSLibraryDirectory, NSUserDomainMask, YES) lastObject];
}

+ (NSError *)copyCachedResultsToFile {
    // Grab the header and footer and put it around the cached data
    NSStringEncoding encoding; NSError *error = nil;
    NSString *htmlHeaderTextPath = [[NSBundle mainBundle] pathForResource:@"HTML_header" ofType:@"html" ]; 
    NSString *htmlHeaderText = [NSString stringWithContentsOfFile:htmlHeaderTextPath usedEncoding:&encoding error:&error];

    NSString *cachedResultsText = [NSString stringWithContentsOfFile:[self cachedResultsFilePath] usedEncoding:&encoding error:&error];
    // Write the results to a file if there are any
    if (cachedResultsText) {
        NSString *htmlFooterTextPath = [[NSBundle mainBundle] pathForResource:@"HTML_footer" ofType:@"html" ]; 
        NSString *htmlFooterText = [NSString stringWithContentsOfFile:htmlFooterTextPath usedEncoding:&encoding error:&error];

        NSString *gameNameHeader = [NSString stringWithFormat:@"<h1>%@ Results for%@%@</h1>",GAME_NAME_TITLE,[self formattedClientName],[self formattedDate] ];
        NSString *tempStringP1 = [htmlHeaderText stringByAppendingString:gameNameHeader];
        NSString *tempStringP2 = [tempStringP1 stringByAppendingString:cachedResultsText];

        NSString *formattedTextForPrinting = [tempStringP2 stringByAppendingString:htmlFooterText];
        NSString *resultsFilePath = [ [Utilities applicationDocumentsDirectory] stringByAppendingPathComponent:[self resultsFileName] ];
        if ( !([[NSFileManager defaultManager] fileExistsAtPath:resultsFilePath]) ) {
            if (! ([[NSFileManager defaultManager] createFileAtPath:resultsFilePath contents:nil attributes:nil]) ) {
                NSLog(@"Error was code: %d - message: %s", errno, strerror(errno));
            }
        }
        NSFileHandle *fileHandler = [NSFileHandle fileHandleForUpdatingAtPath:resultsFilePath];
        [fileHandler writeData:[formattedTextForPrinting dataUsingEncoding:NSUTF8StringEncoding]];
        [fileHandler closeFile];

    }
     return error;
}
@end

Globals in a singleton. Probably not thread-safe, but I don't care right now.

@interface Globals : NSObject {


}
@property (nonatomic, strong) NSString *currentClient;
@property (nonatomic, strong) NSString *showmePict;
@property BOOL checkBoxes;

+ (Globals *)sharedInstance;

- (void)resetClient;

@end

@implementation Globals {

}

static Globals *singleton = nil;
@synthesize currentClient = _currentClient;
@synthesize showmePict = _showmePict;
@synthesize checkBoxes = _checkBoxes;

+(Globals *) sharedInstance {

    NSLog (@"sharedInstance of Globals called.");

    if (nil != singleton) return singleton;
    static dispatch_once_t pred;        // lock
    dispatch_once(&pred, ^{             // this code is at most once
        singleton = [[Globals alloc] init];
    });

    return singleton;

}

- (void)resetClient {
    self.currentClient = nil;
}


@end

Answer 2

Look into using Categories. For the examples you gave, these are methods related to objects of a particular class that happen to be used in several of your own classes. Categories will allow you to park these often used methods where they can be associated with the common factors.

Answer 3

Create a utitity singelton which will be created only ones and then used by the other classes.