Archive/Unarchive Parent-Child objects with a key - objective-c

Question

I have a class A and a subclass B:
#interface A:NSObject<NSCoding>
String a;
String b;
#end
#interface B: A<NSCoding>
int c;
// `a` and `b` attributes are inherited
#end;
I want to archive some objects of A and some of B using attribute a as key.
The encoding and decoding protocols in both class have been defined as:
#implementation A
...
- (void) encodeWithCoder:(NSCoder *)encoder {
//[super encodeWithCoder:encoder];
[encoder encodeObject:self forKey:a];
}
- (id)initWithCoder:(NSCoder *)decoder {
// self = [super initWithCoder:decoder];
if (self=[super init]) {
self = [decoder decodeObjectForKey:a];
}
return self;
}
#end
#implementation B
..
- (void) encodeWithCoder:(NSCoder *)encoder {
[super encodeWithCoder:encoder];
[encoder encodeObject:self forKey:super.a];
}
- (id)initWithCoder:(NSCoder *)decoder {
//self = [super initWithCoder:decoder];
if (self) {
self = [decoder decodeObjectForKey:super.a];
}
return self;
}
For some object list dataArray = [A("One"), B("Two")], the archiving logic is
NSData *data = [NSKeyedArchiver archivedDataWithRootObject:dataArray];
NSError* error = nil;
BOOL success = [data writeToFile: #"xyz.dat" options:0 error: &error];
if (!success)
NSLog( #"error = %#", [error description] );
Again reading from the archived data:
NSData *lD = [[NSData alloc] initWithContentsOfFile:#"xyz.dat"];
NSKeyedUnarchiver *arc = [[NSKeyedUnarchiver alloc] initForReadingWithData:lD];
Now for the object with the attribute a as"One"
While trying to read the object back from archived data, i am getting null!
NSLog(#"Value - %#",[arc decodeObjectForKey:#"One"]);

Answer 1

Maybe,the problem was with encoding self.
I did the following changes:
#implementation A
...
- (void) encodeWithCoder:(NSCoder *)encoder {
if(self.a!=nil)
[encoder encodeObject:self.a forKey:#"a"];
if(self.b!=nil)
[encoder encodeObject:self.b forKey:#"b"];
}
- (id)initWithCoder:(NSCoder *)decoder {
self=[super init];
if (self!=nil) {
self.a= [decoder decodeObjectForKey:#"a"];
self.b= [decoder decodeObjectForKey:#"b"];
}
return self;
}
#end
#implementation B
..
- (void) encodeWithCoder:(NSCoder *)encoder {
[super encodeWithCoder:encoder ];
[encoder encodeObject:self.c forKey:#"c"];
}
- (id)initWithCoder:(NSCoder *)decoder {
if ( (self = [super initWithCoder:decoder ]) )
{
self.c= [decoder decodeObjectForKey:#"c"];
}
return self;
}
While encoding data:
NSMutableDictionary *dict = [NSMutableDictionary new];
[dict setObject:[[A alloc]init()] forKey:#"One"];//say
[dict setObject:[[B alloc]init()] forKey:#"Two"];//say
NSMutableData *yourData = [[NSMutableData alloc] init];
NSKeyedArchiver *archiver = [[NSKeyedArchiver alloc] initForWritingWithMutableData:yourData];
for (NSString* key in dict) {
id value = [dict objectForKey:key];
[archiver encodeObject:value forKey: key];
}
[ archiver finishEncoding];
[yourData writeToFile:#"xyz.dat" atomically:YES];
[yourData release];
[archiver release];
And decoding:
NSData *data = [[NSData alloc] initWithContentsOfFile:#"xyz.dat"];
NSKeyedUnarchiver *keyArc= [[NSKeyedUnarchiver alloc] initForReadingWithData:data];
NSLog(#"%#",[keyArc decodeObjectForKey:#"One"]);
NSLog(#"%#",[keyArc decodeObjectForKey:#"Two"]);
[keyArc finishDecoding];
Ref: https://stackoverflow.com/a/10929284/2301570