gistfile1.m

var WidgetJSON = @"WidgetJSON";
@implementation Screen (CPCoding)
- (id)initWithCoder:(CPCoder)aCoder
{
  // This code will only work when this screen is in the main window - that should 
  // always be the case
  var jsonObject = [aCoder decodeObjectForKey:WidgetJSON];
  return [[CPClassFromString(jsonObject.widgetType) alloc] initFromJSON:jsonObject];
}

- (void)encodeWithCoder:(CPCoder)aCoder
{
  [aCoder encodeObject:[[self toJSON] objectFromJSON] forKey:WidgetJSON];
}

@end