Question

I am working on a project where I have various custom objects. These custom objects (some of which work with nested mutable arrays) need to be saved into a file / or files. What would be the best approach to doing so? Should I create a load & save file manager or would it be a better idea to let each object handle that?

Thank you for your time.

— Steven

Answer 1

Implement NSCoding protocol for you class:

NSString * const kMyArray = @"myString";
NSString * const kMyBool = @"myBool";

- (void)encodeWithCoder:(NSCoder *)coder
{
    [coder encodeObject:_myArray forKey:kMyArray];
    [coder encodeBool:_myBool forKey:kMyBool];
    //...
}

- (id)initWithCoder:(NSCoder *)coder
{
    self = [super init];
    if (self) {
        _myArray = [coder decodeObjectForKey:kMyArray];
        _myBool = [coder decodeBoolForKey:kMyBool];
        //...
    }
    return self;
}

Which allows you to save and load data with NSKeyedArchiver:

//saving collection of Class<NSCoding> objects
NSString *documentsDirectory = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES)[0];
NSString *path = [documentsDirectory stringByAppendingPathComponent:@"data.plist"];
BOOL success = [NSKeyedArchiver archiveRootObject:_collection toFile:path];

//loading
NSData *data = [[NSData alloc] initWithContentsOfFile:path];
if (data) _collection = [NSKeyedUnarchiver unarchiveObjectWithData:data];