NSUserDefaults不会保存NSDictionary

Question

我正在编写一个使用NSUserDefaults作为数据存储机制的应用程序,并且在尝试保存数据时遇到问题(符合属性列表协议):

+ (BOOL)storeAlbum:(Album *)album
{
    NSUserDefaults *prefs = [NSUserDefaults standardUserDefaults];
    NSMutableDictionary *albums = (NSMutableDictionary *)[prefs objectForKey:@"my_adventure_book_albums"];
    NSLog(@"Existing albums: %@",albums);
    if (!albums)
        albums = [NSMutableDictionary dictionaryWithObject:album forKey:@"album"];
    else
        [albums setObject:album forKey:@"album"];
    NSLog(@"%@",album);
    [prefs setObject:albums forKey:@"my_adventure_book_albums"];
    return [prefs synchronize];
}

我得到这个输出:

2010-06-29 17:17:09.929 MyAdventureBook[39892:207] Existing albums: (null)
2010-06-29 17:17:09.930 MyAdventureBook[39892:207] test
2010-06-29 17:17:09.931 MyAdventureBook[39892:207] *** -[NSUserDefaults setObject:forKey:]: Attempt to insert non-property value '{
    album = test;
}' of class 'NSCFDictionary'.

相册的描述方法如下:

- (NSString *)description
{
    // Convert to a NSDictionary for serializing
    if (!title) title = @"";
    if (!date) date = [NSDate dateWithTimeIntervalSinceNow:0];
    if (!coverImage) coverImage = @"";
    if (!images) images = [[NSArray alloc] initWithObjects:@"",nil];

    //NSDictionary *dict = [NSDictionary dictionaryWithObjects:[NSArray arrayWithObjects:title,date,coverImage,images,nil] forKeys:[NSArray arrayWithObjects:@"title",@"date",@"coverImage",@"images",nil]];
    //NSDictionary *dict = [NSDictionary dictionaryWithObjects:[NSArray arrayWithObjects:title,nil] forKeys:[NSArray arrayWithObjects:@"title",nil]];
    //return [dict description];
    return @"test";
}

所有注释掉的行都有相同的结果,所以我决定看看NSString"test"是否可行,它(当然)不会.

Answer 1

但是你放在字典里面的Album*对象,很可能不是属性列表对象,是吗？每个对象,一直向下,需要成为一个属性列表对象才能使其工作.一种description方法不足以实现这一点.

作为一种变通方法,您可以使用NSCoding和NSKeyedArchiver将字典写入a NSData,您可以将其存储在首选项中.

Answer 2

您只能将基本基础类型放入属性列表中.NSUserDefaults将首选项写为属性列表.请参阅此处获取属性列表允许的类型 简而言之,它是数字,字符串,数据,日期,数组和字典.字典必须有字符串键.