Reputation: 709
Update: This works if I call archiveRootObject: from applicationDidFinishLaunching:. If I call it from the init: method of a singleton class, it returns nil.
I'm very confused by the behavior of NSKeyedUnarchiver unarchiveObjectWithFile:. The documentation says that it will return nil if the file doesn't exist. With one of my objects, the following happens:
Game *g1 = [Game getGame];
NSString *archivePath = [Game getArchivePath];
bool success = [NSKeyedArchiver archiveRootObject:g1 toFile:archivePath];
Game *g2 = [NSKeyedUnarchiver unarchiveObjectWithFile:archivePath];
// success is true, g2 is nil
I've verified that the file actually does exist and is getting written to by the archiveRootObject: method. What am I doing wrong preventing me from getting a Game object back out of the archive?
Upvotes: 9
Views: 8332
Reputation: 343
I've meet the same trouble in Xcode 4.1 with ARC support:
BOOL isFileExist = [[NSFileManager defaultManager] fileExistsAtPath:filePath];
NSAssert(isFileExist, @"filePath does not exist");
NSKeyedUnarchiver* coder =
[NSKeyedUnarchiver unarchiveObjectWithFile:filePath]; // nil
NSData* data = [[NSFileManager defaultManager] contentsAtPath:filePath];
coder = [NSKeyedUnarchiver unarchiveObjectWithData:data]; // nil
coder = [[NSKeyedUnarchiver alloc] initForReadingWithData:data]; // OK!!!
It seems to be a bug in cocoa-touch.
Edit:
It is intended to behave like this and is not a bug. But I agree that the naming easily leads to mistakes.
[[NSKeyedUnarchiver alloc] initForReadingWithData:]
returns a NSKeyedUnarchiver
instance.
[NSKeyedUnarchiver unarchiveObjectWithData:]
returns the root object. It is a conviencen method for:
NSKeyedUnarchiver *coder = [[self alloc] initForReadingWithData:arg2];
id object = [coder decodeObjectForKey:@"root"];
Upvotes: 8
Reputation: 31171
You must always -retain
an unarchived object: Game *g2 = [[NSKeyedUnarchiver unarchiveObjectWithFile:archivePath] retain];
Does your g2
conform to NSCoding
? Make sure it does, if it doesn't declare <NSCoding>
in the g2
header. In the implementation file define methods -(id)initWithCoder:(NSCoder *)coder
and -(void)encodeWithCoder:(NSCoder *)coder
If you're struggling to get this to work consider archiving and unarchiving a standard NSObject, like an NSString or some such. You probably don't need to archive a whole custom object, maybe just a remaining time number, game location or position or score. In other words, archive and unarchive the bare minimum you need.
Upvotes: 2