Storing data to a file

load.m

// Fetch NSDictionary containing possible saved state
NSString *errorDesc = nil;
NSPropertyListFormat format;
NSString *plistPath;
NSString *rootPath = [NSSearchPathForDirectoriesInDomains(NSDocumentDirectory,
														  NSUserDomainMask, YES) objectAtIndex:0];
plistPath = [rootPath stringByAppendingPathComponent:@"SavedState.plist"];
NSData *plistXML = [[NSFileManager defaultManager] contentsAtPath:plistPath];
NSDictionary *unarchivedData = (NSDictionary *)[NSPropertyListSerialization
									  propertyListFromData:plistXML
									  mutabilityOption:NSPropertyListMutableContainersAndLeaves
									  format:&format
									  errorDescription:&errorDesc];

// If NSDictionary exists, look to see if it holds a saved game state
if (!unarchivedData)
{
    NSLog(@"Error reading plist: %@, format: %d", errorDesc, format);
} 
else 
{
    // Load property list objects directly
    NSString *myString = [unarchivedData objectForKey:@"MyString"];

    // Load primitives
    NSNumber *boolValue = [unarchivedData objectForKey:@"SomeBoolValue"];
    BOOL someBool = [boolValue boolValue];
    NSNumber *integerValue = [unarchivedData objectForKey:@"SomeIntegerValue"];
    BOOL someBool = [integerValue integerValue];

    // Load your custom objects that conform to NSCoding
    NSData *someObjectData = [unarchivedData objectForKey:@"SomeObject"];
    MyClass *someObject = [NSKeyedUnarchiver unarchiveObjectWithData:someObjectData];
}

save.m

// We're going to save the data to SavedState.plist in our app's documents directory
NSString *rootPath = [NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES) objectAtIndex:0];
NSString *plistPath = [rootPath stringByAppendingPathComponent:@"SavedState.plist"];

// Create a dictionary to store all your data
NSMutableDictionary *dataToSave = [NSMutableDictionary dictionary];

// Store any NSData, NSString, NSArray, NSDictionary, NSDate, and NSNumber directly.  See "NSPropertyListSerialization Class Reference" for more information.
NSString *myString = @"Hello!"
[dataToSave setObject:myString forKey:@"MyString"];

// Wrap primitives in NSValue or NSNumber objects.  Here are some examples:
BOOL someBool = YES;
NSNumber *boolValue = [NSNumber numberWithBool:someBool];
[dataToSave setObject:boolValue forKey:@"SomeBoolValue"];
BOOL someInteger = 99;
NSInteger *integerValue = [NSNumber numberWithInteger:someInteger];
[dataToSave setObject:integerValue forKey:@"SomeIntegerValue"];

// Any objects that conform to NSCoding can be archived to an NSData instance.  In this example, MyClass conforms to NSCoding.
MyClass *someObject = [[MyClass alloc] init];
NSData *archivedStateOfSomeObject = [NSKeyedArchiver archivedDataWithRootObject:someObject];
[dataToSave setObject:archivedStateOfSomeObject forKey:@"SomeObject"];

// Create a serialized NSData instance, which can be written to a plist, from the data we've been storing in our NSMutableDictionary
NSString *errorDescription;
NSData *serializedData = [NSPropertyListSerialization dataFromPropertyList:dataToSave
															        format:NSPropertyListXMLFormat_v1_0
													      errorDescription:&errorDescription];
if(serializedData) 
{
    // Write file
    NSError *error;
    BOOL didWrite = [serializedData writeToFile:plistPath options:NSDataWritingFileProtectionComplete error:&error];

    NSLog(@"Error while writing: %@", [error description]);

    if (didWrite)
        NSLog(@"File did write");
    else
        NSLog(@"File write failed");
}
else 
{
    NSLog(@"Error in creating state data dictionary: %@", errorDescription);
}