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Hello. I’m having trouble trying to get my NSDocument-based app to save / load with NSArchiver. Sorry to post oodles of source, but here’s what I have (I’ll try to comment it along the way):

/* all of the below methods are in MyDocument */

// this method works fine… i end up with a file that contains all my data

// i think this method works… but something isn’t right

/* the below methods are in the Database object */

// again, the methods run, but something is wrong

@interface Database : NSObject { //<-- has nscoding NSMutableArray *items; }

/* below are the methods for the objects inside items */

@interface EssayQuestion : NSObject { //<-- has nscoding NSString *_question; NSString *_comment; }

// and of course there are the appropriate setters and getters…

I’m thinking items might not be retained or something… Thanks, -JohnDevor

Everything looks good to me in this code, so I don’t know why it isn’t working. Is it possible that the table is not retrieving the data correctly? Try logging the number of items in the items array after you decode it:

NSLog(@”items count: %d”, [self database] items] count]);

If it returns zero then you may want to try simplifying the unarchive/archive method. Just for testing, try the single line class methods for archiving and unarchiving. This will result in a binary file instead of an XML Plist which probably isn’t what you want, but if this works then you know it’s something with the archiving/unarchiving.

[[NSData *data = [NSKeyedArchiver archivedDataWithRootObject:[self database]]];


[self setDatabase:[NSKeyedUnarchiver unarchiveObjectWithData:data]];

If the items array does not return zero then I suggest checking the table delegate methods for the error. Hope that helps and good luck.

One more thing, after unarchiving the object, I believe the items array is an NSArray object, not an NSMutableArray. This may be causing problems further in the code. You can convert it to a mutable array using the NSMutableArray arrayWithArray: class method. Someone please correct me if I’m wrong about this one.

– RyanBates

Thanks, I’ll try it when I get home.

Ah! After several hours I found the problem. - init is getting called after - initWithCoder.

Firstly, why is - init getting called at all? Secondly, why is it getting called after my - initWithCoder (it is clearing the variables)?

– JohnDevor

Try putting a break point in the Database init menthod and then running the debugger. It should tell you what is calling the init method. I don’t remember ever having this problem when using NSUnarchiver, are you sure you aren’t calling init somewhere else in the code? Also, what happens if you choose Revert from the file menu after you open a database?

– RyanBates

I’ve searched for every reference of Database and I’m not calling init on it.

The chain of methods leading up to init are:

-[NSDocument loadFileWrapperRepresentation:ofType:]

-[NSDocument readFromFile:ofType:]

-[NSDocument initWithContentsOfFile:ofType:]

-[NSDocumentController makeDocumentWithContentsOfFile:ofType:]

-[NSDocumentController makeDocumentWithContentsOfFile:ofType:]

-[NSDocumentController _openDocumentFileAt:display:]

I just moved all of the files into a brand new project… so it isn’t one of those problems.

Boy, you certianly have a tough one there. The first place I would look is in the Nib file: do you instantiate the Database class in the MyDocument.nib file? Is it even mentioned in there? If so, that is probably calling the init method.

If not, then question is, how does the loadFileWrapperRepresentation:ofType: method know to initialize the Database class? In other words, where does it get that information? You aren’t overriding that method in your NSDocument subclass, are you? I would start by commenting out load data method and see if init is still being called. Slowly limit the problem down by commenting until you find what’s causing it.

If that doesn’t work, you could always find a working example of a simple Document based application and slowly apply your code to it until it breaks. But I always hate to do that…

I don’t know if it will help or not, but here’s a quick tutorial on creating a simple document based text editor:

Good luck,

– RyanBates

Thanks Ryan. I was instaniating my database in the nib. Sorry for your troubles.

– JohnDevor

I’m working on an app which isn’t document based, and instantiates several objects (including the one which I’d like to be the root object) in the nib. Is there any way I can get this to work with NSArchiver? I’ve had zero luck so far.

What problems are you having? I suggest using NSKeyedArchiver if you dont need to support 10.1 or earlier. Archiving is extremely easy to implement. All you need to do is call [NSKeyedArchiver archivedDataWithRootObject:rootObject] to return an NSData object or you can even write directly to a file using [NSKeyedArchiver archiveRootObject:rootObject toFile:filePath]. Note: The object you are archiving must support the NSCoding protocol.– RyanBates

I’m using [NSKeyedArchiver archiveRootObjectToFile:] right now, and when I attempt to load it, I’m getting nil returned for all of my [unarchiver decodeObjectForKey:] calls. I’ll post a link to a test program I made (that also isn’t working) when I get home.

Try using the [NSKeyedUnarchiver unarchiveObjectWithFile:filePath] method. If you are archiving and unarchiving a custom class, then it needs to support it. For example, if you have a class that needs to archive and unarchive a “name” NSString instance variable, you could add these methods to the class:

– RyanBates

Here’s the relevant code quick test program a made so I didn’t have to worry that it was something about my app rather than my understanding of NSArchiver. It doesn’t work right now either. It’s supposed to save an NSString and an NSColor, then load them (they’re displayed in a text field and a color well).

//initWithCoder removed because it isn’t relevant for this

Firstly, you should use accessor methods for setting the myColor and myString methods. If you do not release the old object before setting a new one, there will be a memory leak. Here’s a sample of some accessor methods:

// Use these accessor methods for proper memory management

Secondly, I’m a little confused with the “setStateWithCoder:” method. Are you simply trying to update the controls? If so, I suggest a small “updateControls” method such as this:

You would then need to change the “encodeWithCoder:” and “initWithCoder:” classes. Here’s what I suggest:

Thirdly, it’s generally bad for an object to archive/unarchive itself. I suggest that you create another class to hold all of the data - this is called a model class. Your controller class can then handle the archiving and unarchiving of that model along with updating the controls. Here’s a sample of what the header files might look like for the controller and model classes.

// MyController.h

#import <Cocoa/Cocoa.h>

// Tell the compiler there’s such a thing as a // “MyModel” class so don’t bother giving us an error. @class MyModel;

@interface MyController : NSObject { MyModel *myModel; }

// Accessor methods for proper memory management.


// MyModel.h

#import <Cocoa/Cocoa.h>

// This class holds the coder methods (notice the NSCoding protocal) @interface MyModel : NSObject { NSString *myString; NSColor *myColor; }

// Use these accessor methods for proper memory management


And lastly, for completeness, here’s what the archive and unarchive methods might look like in the MyController class.

I realize I’m throwing a lot at you all at once. Please let me know if you have anymore questions.

– RyanBates

My friend helped me work out the problems in the test app, so now I just have to transfer over the knowledge gained to the main program. Thanks for the help people. –DavidSmith