Objective-C: why my NSString is not retaining its value? - objective-c

Question

The problem lies within the 'initWithCoder' method. When I want to retrieve "Coins_Key" from where I saved it by calling the 'saveData' method in my 'main' class and I pass in the key "self.keyName," the value of keyName is 0.
//Class coins.h
#property (retain) NSString* keyName;
#property (retain) NSString* keyValue;
//Class coins.m
#synthesize keyName;
-(void) saveData:(NSString *)number: (NSString *)keyID
{
self.keyName = keyID;
self.keyValue = number;
}
- (void)encodeWithCoder:(NSCoder *)encoder {
NSLog(#"Encoded keyName: %#", keyName);
[encoder encodeObject:keyValue forKey:keyName];
}
- (id)initWithCoder:(NSCoder *)decoder {
self.keyValue = [decoder decodeObjectForKey:self.keyName];
NSLog(#"Decoded Coins: %#", self.keyValue);
return self;
}
//Class main
[Coins *coin3 = [[Coins alloc] init];
[coin3 saveData:#"6" :#"Coins_Key"];
NSData *data = [NSKeyedArchiver archivedDataWithRootObject:coin3];
coin3 = [NSKeyedUnarchiver unarchiveObjectWithData:data];

Answer 1

You're not quite grasping the encoder/decoder workflow.
Using the encodeObjectForKey: and decodeObjectForKey: methods properly, you should be passing as an argument the key that should be used to store the value. This key must remain constant.
You should also not require callers to provide the key your Coin object uses to store data. Take this simple example as a more correct/efficient method (assuming I understand the purpose of your class):
// Class Coins.h
#property (assign) int numberOfCoins;
// Class Coins.m
#define NUM_COINS_KEY #"NUM_COINS_KEY"
#synthesize numberOfCoins;
- (id)initWithCoder:(NSCoder *)decoder {
if (self = [super init]) { // Use [super initWithCoder:decoder] here if your superclass supports it
self.numberOfCoins = [decoder decodeIntForKey:NUM_COINS_KEY];
NSLog(#"Decoded Coins: %d", self.numberOfCoins);
}
return self;
}
- (void)encodeWithCoder:(NSCoder *)encoder {
NSLog(#"Encoded keyName: %#", keyName);
[encoder encodeInt:self.numberOfCoins forKey:NUM_COINS_KEY];
}
// Class main
Coins *coin = [[Coins alloc] init];
coin.numberOfCoins = 6;
NSData *data = [NSKeyedArchiver archivedDataWithRootObject:coin];
[coin release]; // If you're just playing around, this is probably overkill, but a good habit
coin = [NSKeyedUnarchiver unarchiveObjectWithData:data];