decodeObjectForKey: always returns nil - iphone

Question

I am trying to save my object graph to a file and then reload it at a later time, however decodeObjectForKey: always returns nil for any key I specify.
A binary file is created and does have the occasional human readable text in it, i.e., titleTextColor so I think the archiving process is working.
Have I miss-understood how NSKeyedArchiver and NSKeyedUnarchiver work? Any help would be appreciated.
- (void)encodeWithCoder:(NSCoder *)encoder {
[encoder encodeFloat:titleFontSize forKey:#"titleFontSize"];
[encoder encodeObject:[UIColor orangeColor] forKey:#"titleTextColor"];
[encoder encodeObject:lineSeparatorColor forKey:#"lineSeparatorColor"];
[encoder encodeObject:bodyTextColor forKey:#"bodyTextColor"];
[encoder encodeFloat:bodyTextFontSize forKey:#"bodyTextFontSize"];
[encoder encodeObject:backgroundColor forKey:#"backgroundColor"];
[encoder encodeObject:tintColor forKey:#"tintColor"];
[encoder encodeInteger:bodyTextAlignment forKey:#"bodyTextAlignment"];
[encoder encodeObject:#"Text" forKey:#"Text"];
}
+ (void) saveToFile {
// Get the shared instance
PSYDefaults *sharedInstance = [PSYDefaults sharedInstance];
// Serialise the object
NSData *serializedObject = [NSKeyedArchiver archivedDataWithRootObject:sharedInstance];
// Get the path and filename of the file
NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
NSString *documentsDirectory = [paths objectAtIndex:0];
NSString *pathAndFileName = [documentsDirectory stringByAppendingPathComponent:ksDefaultsFileName];
// Write the defaults to a file
if (serializedObject) [serializedObject writeToFile:pathAndFileName atomically:YES];
}
+ (void) loadFromFile {
// Get the shared instance
PSYDefaults *sharedInstance = [PSYDefaults sharedInstance];
// Get the path and filename of the file
NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
NSString *documentsDirectory = [paths objectAtIndex:0];
NSString *pathAndFileName = [documentsDirectory stringByAppendingPathComponent:ksDefaultsFileName];
NSData *codedData = [[[NSData alloc] initWithContentsOfFile:pathAndFileName] autorelease];
NSKeyedUnarchiver *defaults = [[NSKeyedUnarchiver alloc] initForReadingWithData:codedData];
// Set the properties of the shared instance
NSString *test = [defaults decodeObjectForKey:#"Text"];
NSLog (#"%#", test);
sharedInstance.titleTextColor = [defaults decodeObjectForKey:#"titleTextColor"];
[defaults release];
}
EDIT: Based on advice from DarkDust:
- (id)initWithCoder:(NSCoder *)aDecoder {
self = [super init];
if (self) {
self.titleFontSize = [[aDecoder decodeObjectForKey:#"titleFontSize"] floatValue];
self.titleTextColor = [aDecoder decodeObjectForKey:#"titleTextColor"];
self.lineSeparatorColor = [aDecoder decodeObjectForKey:#"lineSeparatorColor"];
self.bodyTextColor = [aDecoder decodeObjectForKey:#"bodyTextColor"];
self.bodyTextFontSize = [[aDecoder decodeObjectForKey:#"bodyTextFontSize"] floatValue];
self.backgroundColor = [aDecoder decodeObjectForKey:#"backgroundColor"];
self.tintColor = [aDecoder decodeObjectForKey:#"tintColor"];
self.bodyTextAlignment = [[aDecoder decodeObjectForKey:#"bodyTextAlignment"] intValue];
}
return self;
}
and creating a new instance just to test:
+ (void) loadFromFile {
// Get the shared instance
PSYDefaults *sharedInstance = [PSYDefaults sharedInstance];
// Get the path and filename of the file
NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
NSString *documentsDirectory = [paths objectAtIndex:0];
NSString *pathAndFileName = [documentsDirectory stringByAppendingPathComponent:ksDefaultsFileName];
NSData *codedData = [[[NSData alloc] initWithContentsOfFile:pathAndFileName] autorelease];
PSYDefaults *newInstance = [NSKeyedUnarchiver unarchiveObjectWithData:codedData];
sharedInstance.titleTextColor = newInstance.titleTextColor;
}
EDIT - Update (needed to encode floats and ints as NSNumbers)
- (void)encodeWithCoder:(NSCoder *)encoder {
[encoder encodeObject:[NSNumber numberWithFloat:titleFontSize] forKey:#"titleFontSize"];
[encoder encodeObject:titleTextColor forKey:#"titleTextColor"];
[encoder encodeObject:lineSeparatorColor forKey:#"lineSeparatorColor"];
[encoder encodeObject:bodyTextColor forKey:#"bodyTextColor"];
[encoder encodeObject:[NSNumber numberWithFloat:bodyTextFontSize] forKey:#"bodyTextFontSize"];
[encoder encodeObject:backgroundColor forKey:#"backgroundColor"];
[encoder encodeObject:tintColor forKey:#"tintColor"];
[encoder encodeObject:[NSNumber numberWithInt:bodyTextAlignment] forKey:#"bodyTextAlignment"];
}

Answer 1

You serialized using a single root object, but you try to deserialize using a key which doesn't exist at that level.
You want unarchiveObjectWithData:, as in:
NSData *codedData = [[[NSData alloc] initWithContentsOfFile:pathAndFileName] autorelease];
PSYDefaults *decodedDefaults = [NSKeyedUnarchiver unarchiveObjectWithData:codedData];
Note that you'll also need to implement initWithCoder: as counterpart to encodeWithCoder:. Even though it seems you want to have a singleton here, NSCoding demands to create a new object here due to [NSKeyedArchiver archivedDataWithRootObject:sharedInstance].
If you want to en/decode the fields without creating a new instance of PSYDefaults, then you need to use -[NSKeyedArchiver initForWritingWithMutableData:] and pass that archive to a method similar to your encodeWithCoder: (but you should give it a different name then). Then you'd write a counterpart which reads the fields back via a NSKeyedUnarchiver where you do use decodeObjectForKey: and friends for each field.
You also might want to read Apple's Archives and Serializations Programming Guide.

Answer 2

Try to save your object using:
[NSKeyedArchiver archiveRootObject:object toFile:filePath];
and load it using:
[NSKeyedUnarchiver unarchiveObjectWithFile:filePath];
I use above methods to save NSDictionary with custom object to a file.
And also you should have the function initWithCoder:(NSCoder *)decoder in your object.
Which decode the data using
[decoder decodeObjectFoyKey:yourKey];

Answer 3

I had another problem with NSCoder's decodeObjectForKey method while using FXForm - it crashed without any explanation.
- (id)initWithCoder:(NSCoder *)decoder
{
if (self = [super init]) {
self.someObject = [decoder decodeObjectForKey:#"someObject"];
}
return self;
}
The reason was in memory issues. Commonly, looks like when there is no explanation of a bug in logs, it means, it's a memory issue. I forgot to use correct property attribute - copy. I used assign instead. This is correct code:
#interface MyClass : : NSObject <FXForm, NSCoding>
#property (nonatomic, copy) SomeClass *someObject;
#end
Just in case somebody meets this problem too.