Adding serialized permanent data storage to an iOS app

AppDelegate.h

@interface ADKAppDelegate : UIResponder <UIApplicationDelegate>

@property (strong, nonatomic) NSMutableDictionary *storageDict;

-(NSString *)filePath;

@end

AppDelegate.m

static ADKAppDelegate *launchedDelegate;

@implementation AppDelegate

- (NSString *)filePath
{
    NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
    NSString *documentsDirectory = [paths objectAtIndex:0];
    return [documentsDirectory stringByAppendingPathComponent:@"data.archive"];
}

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
    // This is where you decode the data you store.
    
    launchedDelegate = self;
    NSString *filePath = [self filePath];
    if ([[NSFileManager defaultManager] fileExistsAtPath:filePath]) {
        NSData *data = [[NSMutableData alloc] initWithContentsOfFile:filePath];
        NSKeyedUnarchiver *unarchiver = [[NSKeyedUnarchiver alloc] initForReadingWithData:data];
        self.storageDict = [unarchiver decodeObjectForKey:@"dictToSerializeAndSave"];
    }
  return YES;
}

- (void)applicationDidEnterBackground:(UIApplication *)application
{
    // This is where you encode the data you store.
    
    NSMutableData *data = [[NSMutableData alloc] init];
    NSKeyedArchiver *archiver = [[NSKeyedArchiver alloc] initForWritingWithMutableData:data];
    [archiver encodeObject:self.storageDict forKey:@"storageDict"];
    [archiver finishEncoding];
    NSError *error = nil;
    NSString *filePath = [self filePath];
    BOOL success = [data writeToFile:filePath options:NSDataWritingAtomic error: &error];
    if (!success) {
        NSLog(@"writeToFile failed with error %@", error);
    }
}