Write complex object to file objective-c - objective-c

Question

I find it hard to write/read array of custom objects. In my my app, Contact class has a NSDictionary as property and this dictionary has array as objects for keys.
I serialize/deserialize my objects with NSCoder and NSKeyedArchiever and even tried NSPropertyList serialization. I always get errors when serializing as soon as it starts to serialize NSDictionary. Here is my code and I didn't really find a general answer regarding how to serialize custom objects with complex structure?
//Contact.m
//phoneNumbers is a NSDictionary
#pragma mark Encoding/Decoding
-(void)encodeWithCoder:(NSCoder *)aCoder
{
NSLog(#"Encoding");
[aCoder encodeObject:self.firstName forKey:#"firstName"];
NSLog(#"First name encoded");
[aCoder encodeObject:self.lastName forKey:#"lastName"];
NSLog(#"Last name encoded");
[aCoder encodeInt:self.age forKey:#"age"];
NSLog(#"Age encoded");
NSString *errorStr;
NSData *dataRep = [NSPropertyListSerialization dataFromPropertyList:self.phoneNumbers
format:NSPropertyListXMLFormat_v1_0
errorDescription:&errorStr];
NSLog(#"Data class %#", [dataRep class]);
if(!dataRep)
{
NSLog(#"Error encoding %#", errorStr);
}
[aCoder encodeObject:dataRep forKey:#"phones"];
NSLog(#"Encoding finished");
}
- (id) initWithCoder: (NSCoder *)coder
{
if (self = [super init])
{
[self setFirstName:[coder decodeObjectForKey:#"firstName"]];
[self setLastName:[coder decodeObjectForKey:#"lastName"]];
[self setAge:[coder decodeIntForKey:#"age"]];
NSString *errorStr;
NSData *data=[coder decodeObjectForKey:#"phones"];
NSDictionary *propertyList = [NSPropertyListSerialization propertyListFromData:data mutabilityOption:NSPropertyListImmutable format:NULL errorDescription:&errorStr];
if(!propertyList)
{
NSLog(#"Error %#", errorStr);
}
[self setPhoneNumbers:propertyList];
}
return self;
}
//Serializing/Deserializing an array of Contact objects:
#pragma mark Import/Export
//Export Contacts to file
-(void)exportContactsToFile
{
BOOL done=[NSKeyedArchiver archiveRootObject:self.contacts toFile:[PathUtility getFilePath:#"phonebook"]];
NSLog(#"Export done: %i", done);
}
//Import Contacts from file
-(void)importContactsFromFile
{
self.contacts = [NSKeyedUnarchiver unarchiveObjectWithFile:[PathUtility getFilePath:#"phonebook"]];
}
Is there a generic good way to serialize/deserialize objects in objective-c? thanks
The error I get is:
0objc_msgSend
1 CF_Retain
...
that's stack trace, but I get no other errors(

Answer 1

You shouldn't need to use NSPropertyListSerialization for self.phoneNumbers. NSDictionary adheres to the NSCoding protocol.
So, [aCoder encodeObject:self.phoneNumbers forKey:#"phones"]; should be sufficient.
As long as a class adheres to NSCoding (which nearly all Apple-provided class do), you can just use -encodeObject:forKey:, since that method will call that object's implementation of -encodeWithCoder:

Answer 2

I have a special class in my proprietary library that automatically reads the list of its properties and use the getter and setter to encode and decode the object. Sorry I can't share the code here but I can at least give you steps by steps how my class works:
First, the class must be implement NSCoding and NSCopying protocols.
Inside + (void)initialize, iterate thru the definitions of the properties of the class using class_copyPropertyList(), property_getName() and property_copyAttributeList(). Refer Objective-C Runtime Programming Guide for details on these functions.
For each property, run thru its attribute list and get the attribute with strncmp(attribute.name, "T", 1) == 0 (yup, it's a c-string in there). Use that attribute value to determine the type of the property. For example, "i" means int, "I" means unsigned int, if it starts with a "{" then it's a struct etc. Refer this page on the Type Encoding.
Store the property name-type pairs inside a NSDictionary. At the end of properties iteration, store this dictionary inside a static and global NSMutableDictionary using the class name as the key.
To support auto-encoding, implement - (void)encodeWithCoder:(NSCoder *)aCoder to iterate thru the property name-type pair, calling the property getter method (usually - (returnType)propertyName) and encode it inside the coder using appropriate encodeType: method (e.g. encodeInt:, encodeFloat:, encodeObject:, encodeCGPoint: etc).
To support auto-decoding, implement - (id)initWithCoder:(NSCoder *)aDecoder to iterate thru the property name-type pair, decode it from the decoder using appropriate decodeTypeForKey: method (e.g. decodeIntForKey:, decodeFloatForKey:, decodeObjectForKey:, decodeCGPointForKey: etc). and call the property setter method (usually - (void)setPropertyName:).
Implement an instance method that trigger the encoding (luckily I can share this method here ^__^):
NSMutableData *data = [NSMutableData data];
NSKeyedArchiver *arc = [[NSKeyedArchiver alloc] initForWritingWithMutableData:data];
[arc encodeRootObject:self];
[arc finishEncoding];
[arc release];
return data;
Once you have the NSData you can anything with it such as calling writeToFile:atomically: or even [[NSUserDefaults standardUserDefaults] setObject:[self wrapInNSData] forKey:key].
Also, implement a class method that returns a new instance of the object loaded from the file:
NSKeyedUnarchiver *unarc = [[NSKeyedUnarchiver alloc] initForReadingWithData:[NSData dataWithContentsOfFile:dataFilePath]];
MyCoolFileDataStore *data = [unarc decodeObject];
[unarc release];
return data;
Finally, to make another object class supports this auto-encoding-decoding, the class needs to extend the special class.
Sorry, it's a bit long winded, but for my case, the extra trouble that I took to create this class really save a lot of time along the road. Struggle today, breeze through tomorrow ;)