ios storing custom objects

Question

How can I store NSMutableArray of custom objects? I have this code for loading and saving files:

- (NSMutableArray *)loadDataFromFile:(NSString *)fileName {
    NSError *error;
    NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
    NSString *docDir = [paths objectAtIndex:0];
    NSString *path = [docDir stringByAppendingPathComponent:fileName];
    NSFileManager *fileMgr = [NSFileManager defaultManager];
    if (![fileMgr fileExistsAtPath:path]) {
        NSArray *fileArray = [fileName componentsSeparatedByString:@"."];
        NSString *name = [fileArray objectAtIndex:0];
        NSString *ext = [fileArray objectAtIndex:1];
        NSString *bundle = [[NSBundle mainBundle] pathForResource:name ofType:ext];
        [fileMgr copyItemAtPath:bundle toPath:path error:&error];
    }
    NSMutableArray *data = [[NSMutableArray alloc] initWithContentsOfFile:path];
    return data;
}

- (void)saveData:(NSMutableArray *)arrayData toFile:(NSString *)filename forKey:(NSString *)key {
    NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
    NSString *docDir = [paths objectAtIndex:0];
    NSString *path = [docDir stringByAppendingPathComponent:filename];
    [arrayData writeToFile: path atomically:YES];
    NSLog(@"%@", arrayData);
}

But when I used data.plist as filename, it didn't work because NSLog(@"%@", arrayData); returns list custom object adresses:

"AreaTableRecord: 0x76a7ef0"

This custom object is inserted to array using this code:

AreaTableRecord *area=[[AreaTableRecord alloc] init];
        area.title=title;
        area.lastScore=0;
        area.vocabulary=[[NSMutableArray alloc] init];
        [self.areas addObject:area];

How could I store NSMutableArray self.areas that contains custom objects AreaTableRecord? and What file format shloud I use to store this data? (it seems to me that plist is not working in this case)

Answer 1

You are only able to store primitive data types in NSDefaults or a plist. In order to work around this you can either choose to store your information in a database....or encode your objects as byte streams and then save them into a file.

Take a look at this thread. It details how to go about encoding your objects.

Basically you need to add these methods to your custom class:

- (void)encodeWithCoder:(NSCoder *)encoder
{
       //Encode properties, other class variables, etc
    [encoder encodeObject:self.question forKey:@\"question\"];
    [encoder encodeObject:self.categoryName forKey:@\"category\"];
    [encoder encodeObject:self.subCategoryName forKey:@\"subcategory\"];
}


- (id)initWithCoder:(NSCoder *)decoder
{
    self = [super init];
    if( self != nil )
    {
               //decode properties, other class vars
        self.question = [decoder decodeObjectForKey:@\"question\"];
        self.categoryName = [decoder decodeObjectForKey:@\"category\"];
        self.subCategoryName = [decoder decodeObjectForKey:@\"subcategory\"];
    }
    return self;
}

And then in order to use them you make calls as such:

For setting:

NSUserDefaults *defaults = [NSUserDefaults standardUserDefaults];
NSData *myEncodedObject = [NSKeyedArchiver archivedDataWithRootObject:obj];  
[defaults setObject:myEncodedObject forKey:@\"myEncodedObjectKey\"];

For retrieving:

NSUserDefaults defaults = [NSUserDefaults standardUserDefaults];
NSData *myEncodedObject = [defaults objectForKey: key];
MyCustomObject* obj = (MyCustomObject*)[NSKeyedUnarchiver unarchiveObjectWithData: myEncodedObject];