isDirty

- (id)init
{
    if (self = [super init])
    {
        [self addObserver:self forKeyPath:@"isDirty" options:0 context:NULL];
    }
    return self;
}

- (void)dealloc
{
    [self removeObserver:self forKeyPath:@"isDirty"];
}

- (BOOL)loadData
{
    // Load the data, then if successful:
    isDirty = NO;
    return YES;
}

- (BOOL)saveData
{
    if (!self.isDirty)
    {
        return YES;
    }

    // Save the data, then if successful:
    isDirty = NO;
    return YES;
}

// isDirty is dependant on ALL of our declared property.
+ (NSSet *)keyPathsForValuesAffectingIsDirty
{
    unsigned int    num_props;
    objc_property_t *prop_list = class_copyPropertyList(self, &num_props);

    NSMutableSet * propSet = [NSMutableSet set];
    for( unsigned int i = 0; i < num_props; i++ )
    {
        NSString * propName = [NSString stringWithFormat:@"%s", property_getName(prop_list[i])];
        if(![propName isEqualToString:@"isDirty"] )
        {
            [propSet addObject:propName];
        }
    }

    free(prop_list);

    return propSet;
}

// If any of our declared properties are changed, this will be called so set isDirty to true.
- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context
{
    if ([keyPath isEqualToString:@"isDirty"])
    {
        isDirty = YES;
    }
}