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Hello guys,

I have a problem understanding how the NSCoding protocol is meant to work.

Let's describe my situation: I have an NSDocument subclass which only contains a "Canvas *canvas" (a NSView subclass). The canvas has an NSMutableArray of NSDictionary objects. Each NSDictionary has two key/value pairs: one stores an NSBezierPath object and the other stores an NSColor object.

I am trying to get the saving/loading mechanism of NSDocument work in this way: once overridden the readFromData:ofType:error: and the dataOfType:error: methods in such a way that they archive the canvas object, I override initWithCoder: and encodeWithCoder: methods of the canvas itself. Here are my implementations:

In Sketch.m (my NSDocument subclass)

- (NSData *)dataOfType:(NSString *)typeName error:(NSError **)outError {

NSData *data = [NSKeyedArchiverarchivedDataWithRootObject:canvas];

if (!data && outError) {

NSDictionary *d = [NSDictionarydictionaryWithObject:typeName forKey:@"DataType"];

*outError = [NSErrorerrorWithDomain:NSOSStatusErrorDomaincode:unimpErruserInfo:d];

returnnil;

}

return data;

}

- (BOOL)readFromData:(NSData *)data ofType:(NSString *)typeName error:(NSError **)outError {

Canvas *c = nil;

@try {

c = [[NSKeyedUnarchiverunarchiveObjectWithData:data] retain];

} @catch (NSException *exception) {

if (!c && outError) {

NSDictionary *d = [NSDictionarydictionaryWithObject:typeName forKey:@"DataType"];

[d setValue:exception forKey:@"Exception"];

*outError = [NSErrorerrorWithDomain:NSOSStatusErrorDomaincode:unimpErruserInfo:d];

returnNO;

}

}

canvas = c;

NSLog(@"%@",self);

returnYES;

}

In Canvas.m (my NSView subclass)

- (void) encodeWithCoder:(NSCoder *) coder {

[[selfwindow] endEditingFor:nil];

[superencodeWithCoder:coder];

[coder encodeObject:pathsforKey:CNVPathKey];

}

- (id)initWithCoder:(NSCoder *) decoder {

if ( (self = [super initWithCoder:decoder]) ) {

paths = [[decoder decodeObjectForKey:CNVPathKey] retain];

bgColor = [NSColorwhiteColor];

strokeColor = [NSColorblackColor];

}

NSLog(@"Loaded canvas %@.",self);

returnself;

}

That seems to work fine. The methods encode and decode my NSMutableArray and one restored from the archive all data is correct. Then I got the problem. Immediatly after initWithCoder: returns the decoded object, this is litterally thrown away and a new BLANK instance of Canvas gets created, so I am never able to really load anything.

Is there some basis I don't know to get it work? I don't understend why Canvas's init method gets called since initWithCoder: should not call the designated initializer.