iPhone：无法将 NSMutableDictionary 存储到 NSUserDefaults

Question

我正在尝试使用 NSMutableDictionary 实现“添加到收藏夹”功能，因为我必须添加多个键值。即使将对象添加到字典后，以下 addToFavourites 方法也始终显示 Count=0。我读了this 并将nsdefaults 放入mutabledictionary（而不是可变数组）并将结果字典设置回nsdefaults 但不确定是什么问题。任何帮助将非常感激。谢谢。

编辑： 从this 我开始知道我必须在可变和不可变字典中移动数据，然后它就可以正常工作了！但仍然无法将修改后的 NSMutableDictionary 同步到 NSUserDefaults。

-(BOOL)isAddedToFavorites:(NSString*)viewID {
NSUserDefaults *standardUserDefaults = [NSUserDefaults standardUserDefaults];
NSMutableDictionary *favourites = [[standardUserDefaults objectForKey:kFavouriteItemsKey] mutableCopy];

if(favourites && [[favourites objectForKey:kFavouriteItemsKey] objectForKey:viewID])
return YES;

return NO;
}

-(void)addToFavourites:(NSString*)viewID viewType:(NSString*)viewType {
NSMutableDictionary *myMutableDictionary= [NSMutableDictionary dictionaryWithCapacity:[myDictionary count]+1];
[myMutableDictionary addEntriesFromDictionary:myDictionary];
[myMutableDictionary setObject:myObject forKey:myKey];


// Modified dictionary is not getting synced
[[NSUserDefaults standardUserDefaults]  setObject:myMutableDictionary  forKey:kFavouriteItemsKey];
[[NSUserDefaults standardUserDefaults]  synchronize];
}

尝试将字典数据编码为 NSData，经过轻微但严重的更正后它现在可以工作了！

-(BOOL)isAddedToFavorites:(NSString*)viewID {

NSUserDefaults *defaults = [NSUserDefaults standardUserDefaults];
NSData *data = [defaults objectForKey:kFavouriteItemsKey];
NSDictionary *favourites = [NSKeyedUnarchiver unarchiveObjectWithData:data]; 

if(favourites && [favourites objectForKey:viewID])
    return YES;

return NO;
}

-(void)addToFavourites:(NSString*)viewID viewType:(NSString*)viewType {

NSUserDefaults *defaults = [NSUserDefaults standardUserDefaults];
NSData *data = [defaults objectForKey:kFavouriteItemsKey];
NSDictionary *myDictionary = [NSKeyedUnarchiver unarchiveObjectWithData:data]; 

NSMutableDictionary *myMutableDictionary= [NSMutableDictionary dictionaryWithCapacity:[myDictionary count]+1];
[myMutableDictionary addEntriesFromDictionary:myDictionary];
[myMutableDictionary setObject:viewType forKey:viewID];


NSData *newdata = [NSKeyedArchiver archivedDataWithRootObject:myMutableDictionary];
[[NSUserDefaults standardUserDefaults] setObject:newdata forKey:kFavouriteItemsKey];
[[NSUserDefaults standardUserDefaults] synchronize];
}

谢谢。

Answer 1

您需要为字典中的元素实现此功能：

字典中的元素实现

@interface CommentItem : NSObject<NSCoding> {
    NSString *value;
}

然后在CommentItem的实现中，提供了两个方法：

-(void)encodeWithCoder:(NSCoder *)encoder
{
    [encoder encodeObject:value forKey:@"Value"];
}

-(id)initWithCoder:(NSCoder *)decoder
{
    self.value = [decoder decodeObjectForKey:@"Value"];
    return self;
}

正如@Irene 提供的链接所建议的那样。