How to Archive Two Arrays with NSKeyedArchiver

Question

I've read a lot about archiving a single array with NSKeyedArchiver. But how would I save two arrays?

I need to store/retrieve data for two view controllers within a UITabBarController. Each of the two view controllers create objects of the same custom class, but store them in a separate array for each view controller.

My current code uses a separate method for saving each array. The problem is that when archiving the second array, it overrides the first one. I can't get them both to save. I think I either need to save the two arrays to their own file or combine the data into a single file. I'm just not sure how to write the code for this. Can anyone help??

- (void)saveFermentableIngredients
{
    NSMutableData *fermentableData = [[NSMutableData alloc] init];
    NSKeyedArchiver *fermentableArchiver = [[NSKeyedArchiver alloc] initForWritingWithMutableData:fermentableData];
    [fermentableArchiver encodeObject:self.fermentableIngredients forKey:@"FermentableIngredients"];
    [fermentableArchiver finishEncoding];
    [fermentableData writeToFile:[self dataFilePath] atomically:YES];
}

- (void)saveHopIngredients
{
    NSMutableData *hopData = [[NSMutableData alloc] init];
    NSKeyedArchiver *hopArchiver = [[NSKeyedArchiver alloc] initForWritingWithMutableData:hopData];
    [hopArchiver encodeObject:self.hopIngredients forKey:@"HopIngredients"];
    [hopArchiver finishEncoding];
    [hopData writeToFile:[self dataFilePath] atomically:YES];
}

I should mention that I've done the usual setup here with implementing the initWithCoder and encodeWithCoder methods. I suspect the problem is really in the code I posted above.

Answer 1

I ended up saving each array to a separate file. First I declared the two separate file paths like this:

- (NSString *)fermentableDataFilePath
{
    return [[self documentsDirectory] stringByAppendingPathComponent:@"Fermentables.plist"];
}

- (NSString *)hopDataFilePath
{
    return [[self documentsDirectory] stringByAppendingPathComponent:@"Hops.plist"];
}

Then I referenced each file path in the save methods I put in my original question. So in the first method I would have written my writeToFile method like this:

[fermentableData writeToFile:[self fermentableDataFilePath] atomically:YES];

Answer 2

If you want all of this data stored together then you should do something like:

- (void)encodeWithCoder:(NSCoder *)aCoder {
    [aCode encodeObject:self.fermentableIngredients forKey:@"FermentableIngredients"];
    [aCode encodeObject:self.hopIngredients forKey:@"HopIngredients"];
}

Answer 3

Another method of solving this issue is to put the two (or more) arrays into a dictionary. Then you can archive the dictionary into a single file and retrieve the arrays using the keys you assign. You can archive multiple items in this manner without resorting to NSCoder or creating multiple archives. The one limitation, as it's a dictionary, is that the values you store must all be of the same type. I've archived a dictionary of SCNNode arrays in this manner and it worked well.