Saving an NSMutableArray to a plist file using NSKeyedArchiver and NSCoding.

YourMainDataModel.m

// Gets the path to the app's Documents folder
- (NSString *)documentsDirectory
{
    NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
    return paths[0];
}

// Gets the path to the data file
- (NSString *)dataFilePath
{
    return [[self documentsDirectory] stringByAppendingPathComponent:@"YOUR-FILENAME-HERE.plist"];
}

// Loads the array from the file or creates a new array if no file present
- (NSMutableArray *)loadArray
{
    NSMutableArray *array;
    NSString *path = [self dataFilePath];
    if ([[NSFileManager defaultManager] fileExistsAtPath:path]) {
        NSData *data = [[NSData alloc] initWithContentsOfFile:path];
        NSKeyedUnarchiver *unarchiver = [[NSKeyedUnarchiver alloc] initForReadingWithData:data];
        array = [unarchiver decodeObjectForKey:@"MY_ARRAY"];
        [unarchiver finishDecoding];
    } else {
        array = [[NSMutableArray alloc] initWithCapacity:20];
    }
    return array;
}

// Saves the array to a file
- (void)saveArray:(NSMutableArray *)array
{
    NSMutableData *data = [[NSMutableData alloc] init];
    NSKeyedArchiver *archiver = [[NSKeyedArchiver alloc] initForWritingWithMutableData:data];
    [archiver encodeObject:array forKey:@"MY_ARRAY"];
    [archiver finishEncoding];
    [data writeToFile:[self dataFilePath] atomically:YES];
}

YourObject.h

// Make the object conform to the NSCoding protocol
@interface YourObject : NSObject <NSCoding>

@property (nonatomic, copy) NSString *name;
// and other properties here...

@end

YourObject.m

#import "YourObject.h"

@implementation YourObject

- (id)init
{
    if ((self = [super init])) {
        self.name = @"Some default name";
        // initialize any other properties here
    }
    return self;
}

- (id)initWithCoder:(NSCoder *)aDecoder
{
    if ((self = [super init])) {
        self.name = [aDecoder decodeObjectForKey:@"Name"];
        // decode any other properties here
    }
    return self;
}
 
- (void)encodeWithCoder:(NSCoder *)aCoder
{
    [aCoder encodeObject:self.name forKey:@"Name"];
    // encode any other properties here
}

@end