How to use NSCoder - iphone

Question

I am developing iphone application.
I use NSCoder.
MyApplication.h
#define ITEMS_KEY #"items"
#define CATEGORIES_KEY #"categories"
#import <UIKit/UIKit.h>
#interface MyApplicationData : NSObject <NSCoding, NSCopying> {
NSMutableArray* items;
NSMutableArray* categories;
}
#property (nonatomic ,retain) NSMutableArray* items;
#property (nonatomic, retain) NSMutableArray* categories;
#end
Myapplication.m
#import "MyApplicationData.h"
#implementation MyApplicationData
#synthesize items;
#synthesize categories;
#pragma mark NSCoding
- (void)encodeWithCoder:(NSCoder *)aCoder{
[aCoder encodeObject:items forKey:ITEMS_KEY];
[aCoder encodeObject:categories forKey:CATEGORIES_KEY];
}
-(id)initWithCoder:(NSCoder *)aDecoder{
if(self = [super init]){
self.items = [aDecoder decodeObjectForKey:ITEMS_KEY];
self.categories = [aDecoder decodeObjectForKey:CATEGORIES_KEY];
}
return self;
}
#pragma mark -
#pragma mark NSCopying
-(id)copyWithZone:(NSZone *)zone{
MyApplicationData* copy = [[[self class]allocWithZone:zone]init];
items = [self.items copy];
categories = [self.categories copy];
return copy;
}
#end
But warnning.
'NSCoder' may not respond to '-decodeDataObjectForKey'
How to use NSCoder?

Answer 1

Use -decodeObjectForKey: and read the documentation.

Answer 2

Here is the NSCoding protocal methods from my LogEntry object, you can ignore the switch statement and the schema details though, those are from a base class I have written that allows me to keep sane track of changing data formats.
Please note that in addition to using decodeObjectForKey: you also need to make sure you retain/copy the given values as they are autoreleased when received.
- (id)initWithCoder:(NSCoder *)coder {
self = [super initWithCoder:coder];
if (self != nil) {
switch ([schemaVersion intValue]) {
case 2:
filepath = [[coder decodeObjectForKey:#"filepath"] copy];
identifier = [coder decodeInt64ForKey:#"identifier"];
level = [coder decodeIntForKey:#"level"];
lineNumber = [[coder decodeObjectForKey:#"lineNumber"] retain];
message = [[coder decodeObjectForKey:#"message"] retain];
timestamp = [[coder decodeObjectForKey:#"timestamp"] retain];
break;
default:
[self release], self = nil;
break;
}
}
return self;
}
- (void)encodeWithCoder:(NSCoder *)coder {
[coder encodeObject:filepath forKey:#"filepath"];
[coder encodeInt64:identifier forKey:#"identifier"];
[coder encodeInt:level forKey:#"level"];
[coder encodeObject:lineNumber forKey:#"lineNumber"];
[coder encodeObject:message forKey:#"message"];
[coder encodeObject:timestamp forKey:#"timestamp"];
[super encodeWithCoder:coder];
}

Answer 3

I think you should be using -decodeObjectForKey:

Answer 4

I wrote a helper function for using NSCoding. It's a part of VSCore Library. Check it out here:
#interface QuickCoding : NSObject
+ (void)quickEncode:(NSObject<NSCoding>*)object withEncoder:(NSCoder*)encoder;
+ (void)quickDecode:(NSObject<NSCoding>*)object withDecoder:(NSCoder*)decoder;
#end
And the .m file:
#import "QuickCoding.h"
#import "ReflectionHelper.h"
#define QUICK_CODING_HASH #"h4"
#implementation QuickCoding
+ (void)quickEncode:(NSObject<NSCoding>*)object withEncoder:(NSCoder *)encoder{
NSArray *codingKeys = [ReflectionHelper fieldsList:[object class]];
NSUInteger hash = [[codingKeys componentsJoinedByString:#""] hash];
[encoder encodeObject:#(hash) forKey:QUICK_CODING_HASH];
[codingKeys enumerateObjectsUsingBlock:^(NSString *key, __unused NSUInteger idx, __unused BOOL *stop) {
id val = [object valueForKey:key];
if ([val conformsToProtocol:#protocol(NSCoding)]){
[encoder encodeObject:val forKey:key];
}
}];
}
+ (void)quickDecode:(NSObject<NSCoding>*)object withDecoder:(NSCoder *)decoder{
NSArray *codingKeys = [ReflectionHelper fieldsList:[object class]];
NSUInteger hash = [[codingKeys componentsJoinedByString:#""] hash];
NSUInteger decodedHash = [[decoder decodeObjectForKey:QUICK_CODING_HASH] unsignedIntegerValue];
BOOL equalHash = hash == decodedHash;
[codingKeys enumerateObjectsUsingBlock:^(NSString *key, __unused NSUInteger idx, __unused BOOL *stop) {
id val = [decoder decodeObjectForKey:key];
if (equalHash || val){
[object setValue:val forKey:key];
}
}];
}
#end
Full code is here: https://github.com/voipswitch/VSCore/tree/master/VSCore/Storage