从NSKeyedArchiver加载单例状态

这就是我认为这是错误的地方。您熟悉NSCoding,通常通过encodeWithCoder:和initWithCoder:重写使对象可编码来采用它。更简单的是,您仍然可以使用NSCoding和nscoder,而无需重写这些方法。您可以对共享对象的状态进行编码,而无需对共享对象本身进行编码。这就避免了解码共享对象的尴尬问题。

下面是一个我认为你可以做的例子:

@implementation MySharedObject
+ (id)sharedInstance {
    static id sharedInstance = nil;
    if (!sharedInstance) {
        sharedInstance = [[MyClass alloc] init];
    }
}

- (id)init {
    if ((self = [super init])) {
        NSData *data = /* probably from user defaults */
        if (data) { // Might not have any initial state.
            NSKeyedUnarchiver *coder = [[[NSKeyedUnarchiver alloc] initForReadingWithData:data] autorelease];
            myBoolean = [coder decodeBoolForKey:@"MyBoolean"];
            myObject = [[coder decodeObjectForKey:@"MyObject"] retain];
            [coder finishDecoding];
        }
    }
    return self;
}

- (void)saveState {
    NSMutableData *data = [NSMutableData data];
    NSKeyedArchiver *coder = [[[NSKeyedArchiver alloc] initForWritingWithMutableData:data] autorelease];
    [coder encodeBool:myBoolean forKey:@"MyBoolean"];
    [coder encodeObject:myObject forKey:@"MyObject"];
    [coder finishEncoding]
    // Save the data somewhere, probably user defaults...   
}
@end

这里我们有一个共享对象,它使用键控归档来持久化配置,但我们不编码共享对象本身。这避免了解码singleton类的第二个实例的尴尬问题。

您需要在单例本身中进行加载,这里要做的是创建单例,将lval分配给单例,然后创建一个新对象,并在不修改单例的情况下将lval重新分配给该新对象。换言之:

//Set venue to point to singleton
Venue *venue = [Venue sharedVenue];

//Set venue2 to point to singleton
Venue *venue2 = [Venue sharedVenue];

NSData *data = [[NSMutableData alloc] initWithContentsOfFile:[self dataFilePath]];
NSKeyedUnarchiver *unarchiver = [[NSKeyedUnarchiver alloc] initForReadingWithData:data];

//Set venue to unarchived object (does not change the singleton or venue2)
venue = [unarchiver decodeObjectForKey:@"Venue"];
[unarchiver finishDecoding];

你要做的是在sharedVenue中处理这个问题。人们做单身有几种方式,所以我不能确定你在做什么,但让我们假设sharedVenue目前看起来像这样:

static Venue *gSharedVenue = nil;

- (Venue *) sharedVenue {
  if (!gSharedVenue) {
    gSharedVenue = [[Venue alloc] init];
  }

  return gSharedVenue;
}

static Venue *gSharedVenue = nil;

- (Venue *) sharedVenue {
  if (!gSharedVenue) {
    NSData *data = [[NSMutableData alloc] initWithContentsOfFile:[self dataFilePath]];
    NSKeyedUnarchiver *unarchiver = [[NSKeyedUnarchiver alloc] initForReadingWithData:data];
    [data release];

    gSharedVenue = [unarchiver decodeObjectForKey:@"Venue"];
    [unarchiver finishDecoding];
    [unarchiver release];
  }

  if (!gSharedVenue) {
    gSharedVenue = [[Venue alloc] init];
  }

  return gSharedVenue;
}

显然,您需要以某种方式传递归档对象文件的实际路径。

好的,如果您使用的是基于alloc的singleton,则需要在classes init方法中处理此问题:

- (id) init {
  self = [super init];

  if (self) {
    NSData *data = [[NSMutableData alloc] initWithContentsOfFile:[self dataFilePath]];
    NSKeyedUnarchiver *unarchiver = [[NSKeyedUnarchiver alloc] initForReadingWithData:data];
    [data release];

    Venue *storedVenue = [unarchiver decodeObjectForKey:@"Venue"];
    [unarchiver finishDecoding];
    [unarchiver release];

    if (storeVenue) {
       [self release];
       self = [storedVenue retain];
    }

  }

  return self;
}