How to display unarchived custom NSView objects

I am involved with Cocoa programming and Im not able to figure out how to archive and unlock a custom NSView subclass

I've created a toy app that presents a window. This window contains an instance of my custom BackgroundView class (archived xib file). Clicking anywhere on this BackgroundView creates and displays a blue square that originates from the clicked point. This square is an instance of my square class. This all works as I expect.

The Square class implements the NSCoding protocol. I added dataOfType: typeName: error: and readfromData: ofType: error: methods to the MyDocument class. As far as I can tell from the log statements, Squares are zipped to a file and unzipped when the file is downloaded. But I was unable to get the squares to display themselves on the window. Square's drawWithRect: method never gets called, although I've called setNeedsDisplay: YES on every square.

The code looks like this:

Square.h
#import <Cocoa/Cocoa.h>
@interface Square : NSView <NSCoding> {
}
@end

Square.m
#import "Square.h"
@implementation Square

- (id)initWithFrame:(NSRect)frame {
   self = [super initWithFrame:frame];
   return self;
}

- (void)drawRect:(NSRect)rect {
       [[NSColor blueColor] set];
       NSBezierPath *newPath = [NSBezierPath bezierPathWithRect:[self bounds]];
       [newPath fill];
}

-(void)encodeWithCoder:(NSCoder *)coder
{
       [coder encodeRect:[self frame] forKey:@"frame"];
}

-(id)initWithCoder:(NSCoder *)coder
{
       NSRect theRect = [coder decodeRectForKey:@"frame"];
       self = [super initWithFrame:theRect];
       return self;
}
@end
-----
BackgroundView.h
#import <Cocoa/Cocoa.h>
@interface BackgroundView : NSView {
}
@end

BackgroundView.m
#import "BackgroundView.h"
#import "Square.h"
@implementation BackgroundView

- (id)initWithFrame:(NSRect)frame {
   self = [super initWithFrame:frame];
   if (self) {
       // Initialization code here.
   }
   return self;
}

- (void)drawRect:(NSRect)rect {
       for (Square *subview in self.subviews)
               [subview setNeedsDisplay:YES];
}

-(void)mouseDown:(NSEvent *)theEvent {
       NSPoint unsetClick = [theEvent locationInWindow];
       NSPoint theClick = [self convertPoint:unsetClick fromView:nil];
       NSRect theRect;
       theRect.origin = theClick;
       theRect.size.width = 100.00;
       theRect.size.height = 100.00;
       Square *newSquare = [[Square alloc] initWithFrame:theRect];
       [self addSubview:newSquare];
       [newSquare setNeedsDisplay:YES];
}
@end
------
MyDocument.h
#import <Cocoa/Cocoa.h>
@class BackgroundView;

@interface MyDocument : NSDocument
{
       IBOutlet BackgroundView *theBackgroundView;
}
@end

MyDocument.m
#import "MyDocument.h"

@implementation MyDocument

- (id)init
{
   self = [super init];
   return self;
}

- (NSString *)windowNibName
{
   return @"MyDocument";
}

- (void)windowControllerDidLoadNib:(NSWindowController *) aController
{
   [super windowControllerDidLoadNib:aController];
}

- (NSData *)dataOfType:(NSString *)typeName error:(NSError **)outError
{
   return [NSKeyedArchiver
archivedDataWithRootObject:[theBackgroundView subviews]];
   if ( outError != NULL ) {
               *outError = [NSError errorWithDomain:NSOSStatusErrorDomain
code:unimpErr userInfo:NULL];
       }
       return nil;
}

- (BOOL)readFromData:(NSData *)data ofType:(NSString *)typeName
error:(NSError **)outError
{
   [theBackgroundView setSubviews:[NSKeyedUnarchiver
unarchiveObjectWithData:data]];
   [theBackgroundView setNeedsDisplay:YES];
   if ( outError != NULL ) {
               *outError = [NSError errorWithDomain:NSOSStatusErrorDomain
code:unimpErr userInfo:NULL];
       }
   return YES;
}

@end