在自定义类的子类上使用 NSCoding

Question

我正在使用 NSCoding 来归档/取消归档自定义类作为数据持久性的方法。如果该对象是 NSObject 的子类，那么它工作得很好，但我也有作为自定义对象的子类的对象。我是否需要更改 initWithCoder: 方法以及encodeWithCoder？现在，特定于子类的属性可以很好地编码/解码，但子类从超类继承的属性则不能。有什么想法吗？这是基本结构：

@interface NewsItem : NSObject <NSCoding, NSCopying> {
//properties for the super class here
}

@implementation NewsItem
- (void)encodeWithCoder:(NSCoder *)coder {
    [coder encodeObject:itemName forKey:kItemNameKey];
//etc etc
}

- (id)initWithCoder:(NSCoder *)coder {
    if ( (self = [super init]) )
    {
        self.itemName = [coder decodeObjectForKey:kItemNameKey];
//etc etc
    }
    return self;
}

-(id)copyWithZone:(NSZone *)zone {
    NewsItem *copy = [[[self class] allocWithZone: zone] init];
    copy.itemName = [[self.itemName copy] autorelease];
//etc etc
    return copy;
}

和子类：

@interface File : NewsItem {
    NSString *fileSizeString;
//etc etc
}

@implementation File
- (void)encodeWithCoder:(NSCoder *)coder {
    [super encodeWithCoder:coder]; //added this, but didn't seem to make a difference
    [coder encodeObject:fileSizeString forKey:kFileSizeStringKey];
//etc etc

}

- (id)initWithCoder:(NSCoder *)coder {
    if ( (self = [super init]) )
    {
        self.fileSizeString = [coder decodeObjectForKey:kFileSizeStringKey];
//etc etc
    }
    return self;
}

-(id)copyWithZone:(NSZone *)zone {
    File *copy = (File *)[super copyWithZone:zone];
    copy.fileSizeString = [[self.fileSizeString copy] autorelease];
//etc etc
    return copy;
}

Answer 1

在 File 的 initWithCoder: 方法中

if ( (self = [super init]) )

应该是

if ( (self = [super initWithCoder:coder]) )

Answer 2

您应该在子类中调用 NSCoding 方法的超类实现

- (id)initWithCoder:(NSCoder *)coder {
    if ( (self = [super initWithCoder:coder]) )
    {
        self.fileSizeString = [coder decodeObjectForKey:kFileSizeStringKey];
    }
    return self;
}