Error trying to archive custom object in Xcode

Question

I am trying to use NSCoder to archive a custom object (my object is a library, as in a place to check out books) to the iPhone's file system. However, I am getting an error "unrecognized selector sent to instance" when I attempt to call NSKeyedArchiver archiveRootObject. The library declares the NSCoding protocol and implements the required methods. I'm at a loss.

The object Interface (library.h):

#import <Foundation/Foundation.h>
@interface Library : NSObject <NSCoding> {
int numCopies;
NSString *location;
NSString *locationInfo;
NSString *material; 
NSString *library;
}
+ (id)library;
@property (nonatomic) int numCopies;
@property (retain) NSString *location;
@property (retain) NSString *locationInfo;
@property (retain) NSString *material;
@property (retain) NSString *library;
- (void)encodeWithCoder:(NSCoder *)encoder;
- (void)initWithCoder:(NSCoder *)decoder;
@end

The relevant part of object implementation (library.m):

#import "library.h"

@implementation Library

@synthesize numCopies;
@synthesize location;
@synthesize locationInfo;
@synthesize material;
@synthesize library;

+ (id)library
{
return [[Library alloc] init];  
}

-(void)encodeWithCoder:(NSCoder *)encoder
{
    //for each instance variable, archive it under its variable name
    [encoder encodeObject:numCopies forkey:@"numCopies"];
    [encoder encodeObject:location forkey:@"location"];
    [encoder encodeObject:locationInfo forkey:@"locationInfo"];
    [encoder encodeObject:material forkey:@"material"];
    [encoder encodeObject:library forkey:@"library"];
}

Finally, the viewController (libTableViewController.m)

//try to archive the library object
NSString *savePath = pathInDocumentDirectory(@"lib.data");
NSLog(@"try to archive library to path: %@", savePath);
[NSKeyedArchiver archiveRootObject:this_lib toFile:savePath];

Here is the error:

2011-12-18 12:13:38.799 LibraryFiend2[12877:207] try to archive library to path: /Users/kclary/Library/Application Support/iPhone Simulator/4.3/Applications/71B11434-3307-449A-9E95-5E22034E7FA0/Documents/lib.data
2011-12-18 12:13:38.800 LibraryFiend2[12877:207] -[NSKeyedArchiver encodeObject:forkey:]: unrecognized selector sent to instance 0x4b1a130
2011-12-18 12:13:38.801 LibraryFiend2[12877:207] *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[NSKeyedArchiver encodeObject:forkey:]: unrecognized selector sent to instance 0x4b1a130'
terminate called after throwing an instance of 'NSException'

If I substitute a simple array for my library object, it works.

Evgeny Shurakov · Accepted Answer · 2011-12-21 05:28:45Z

2

You got exception because of this line [encoder encodeObject:numCopies forkey:@"numCopies"];

numCopies is not an object, it's a primitive and should be stored using encodeInt:forKey: method.

answered Dec 21, 2011 at 5:28

Evgeny Shurakov

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1 Comment

Kevin Clary Over a year ago

Unfortunately, that did not fix the problem. I changed the line to: [encoder encodeInt:numCopies forkey:@"numCopies"]; but I am getting the same exception on that line of code.

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