xcode 为什么 NSUserDefaults 无法保存 NSMutableDictionary？
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Why does NSUserDefaults fail to save NSMutableDictionary?
提问by user1940136
I'm trying to save a NSMutableDictionarywith NSUserDefaults. I read many posts on the topic in stackoverflow... I also found one option that worked; however unfortunately it worked only once and then it started to save (null) only.
Does anybody have a hint?
我正在尝试保存一个NSMutableDictionarywith NSUserDefaults。我在 stackoverflow 中阅读了许多关于该主题的帖子......我还找到了一个有效的选项；然而不幸的是它只工作了一次然后它开始只保存（空）。有人有提示吗？
Thanks
谢谢
Code to save:
保存代码：
[[NSUserDefaults standardUserDefaults] setObject:[NSKeyedArchiver archivedDataWithRootObject:dictionary] forKey:@"Key"];
[[NSUserDefaults standardUserDefaults] synchronize];
Code to load:
加载代码：
NSMutableDictionary *dictionary = [[NSMutableDictionary alloc]init];
NSData *data = [[NSUserDefaults standardUserDefaults]objectForKey:@"Key"];
dictionary = [NSKeyedUnarchiver unarchiveObjectWithData:data];
Code to add Objects to the NSMutableDictionary:
将对象添加到 的代码NSMutableDictionary：
[dictionary setObject:[NSNumber numberWithInt:0] forKey:@"Key 1"];
[dictionary setObject:[NSNumber numberWithInt:1] forKey:@"Key 2"];
[dictionary setObject:[NSNumber numberWithInt:2] forKey:@"Key 3"];
Code to NSLog() values:
NSLog() 值的代码：
for (NSString * key in [dictionary allKeys]) {
NSLog(@"key: %@, value: %i", key, [[dictionary objectForKey:key]integerValue]);
}
And also the keys are (null):
而且键是（空）：
NSLog(@"%@"[dictionary allKeys]);
回答by zaph
From Apple's documentation for NSUserDefaults objectForKey:
The returned object is immutable, even if the value you originally set was mutable.
来自 Apple 的文档NSUserDefaults objectForKey：
返回的对象是不可变的，即使您最初设置的值是可变的。
The line:
线路：
dictionary = [NSKeyedUnarchiver unarchiveObjectWithData:data];
discards the previously created NSMutableDictionaryand returns a NSDictionary.
丢弃先前创建的NSMutableDictionary并返回一个NSDictionary.
Change the loading to:
将加载更改为：
NSData *data = [[NSUserDefaults standardUserDefaults]objectForKey:@"Key"];
dictionary = [NSKeyedUnarchiver unarchiveObjectWithData:data];
Complete example, there is also no need to use NSKeyedArchiverin this example:
完整的例子，NSKeyedArchiver在这个例子中也没有必要使用：
NSDictionary *firstDictionary = @{@"Key 4":@4};
[[NSUserDefaults standardUserDefaults] setObject:firstDictionary forKey:@"Key"];
NSMutableDictionary *dictionary = [[[NSUserDefaults standardUserDefaults] objectForKey:@"Key"] mutableCopy];
dictionary[@"Key 1"] = @0;
dictionary[@"Key 2"] = @1;
dictionary[@"Key 3"] = @2;
for (NSString * key in [dictionary allKeys]) {
NSLog(@"key: %@, value: %@", key, [dictionary objectForKey:key]);
}
NSLog output:
key: Key 2, value: 1
key: Key 1, value: 0
key: Key 4, value: 4
key: Key 3, value: 2
NSLog 输出：
key: Key 2, value: 1
key: Key 1, value: 0
key: Key 4, value: 4
key: Key 3, value: 2
