Question

I’m learning Cocoa programming, and I’m unable to figure out how to
archive and unarchive a custom NSView subclass

I’ve made a toy application that presents a window. This window
contains an instance of my custom BackgroundView class (archived in
the xib file). Clicking anywhere in this BackgroundView creates and
displays a blue square whose origin is the click point. This square is
an instance of my Square class. All of this works as I expect.

The Square class implements the NSCoding protocol. I’ve added
dataOfType: typeName: error: and readfromData: ofType: error: methods
to the MyDocument class. As far as I can tell from log statements, the
Squares are being archived to the file, and unarchived when the file
is loaded. But I’m unable to make the squares display themselves on
the window. The Square class’s drawWithRect: method is never called,
even though I’ve called setNeedsDisplay:YES on each square.

The code is as follows:

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

Answer 1

Since Square is a subclass of NSView, and NSView also implements NSCoding, you need to invoke super’s implementation of both encodeWithCoder: and initWithCoder:.

@implementation Square
- (id)initWithFrame:(NSRect)frame
{
    return [super initWithFrame:frame];
}

-(id)initWithCoder:(NSCoder *)coder
{
    if ((self = [super initWithCoder:coder]))
    {
        NSRect theRect = [coder decodeRectForKey:@"frame"];
        self = [super initWithFrame:theRect];
        return self;
    }
}

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

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