为什么 NSUserDefaults 无法在 iOS 中保存 NSMutableDictionary?

Why NSUserDefaults failed to save NSMutableDictionary in iOS?(为什么 NSUserDefaults 无法在 iOS 中保存 NSMutableDictionary?)

问题描述

我想在 NSUserDefaults 中保存一个 NSMutableDictionary 对象.NSMutableDictionary 中的键类型是 NSString，值类型是 NSArray，其中包含实现 NSCoding.每个文档，NSString 和 NSArray 都符合 NSCoding.

I'd like to save an NSMutableDictionary object in NSUserDefaults. The key type in NSMutableDictionary is NSString, the value type is NSArray, which contains a list of object which implements NSCoding. Per document, NSString and NSArray both are conform to NSCoding.

我收到此错误:

[NSUserDefaults setObject: forKey:]: 尝试插入 NSCFDictionary 类的非属性值.....

[NSUserDefaults setObject: forKey:]: Attempt to insert non-property value.... of class NSCFDictionary.

推荐答案

我找到了一种替代方法，在保存之前，我使用 NSKeyedArchiverNSArray 对象)进行编码>，以 NSData 结尾.然后使用 UserDefaults 保存 NSData.

I found out one alternative, before save, I encode the root object (NSArray object) using NSKeyedArchiver, which ends with NSData. Then use UserDefaults save the NSData.

当我需要数据时，我读出NSData，并使用NSKeyedUnarchiver 将NSData 转换回对象.

When I need the data, I read out the NSData, and use NSKeyedUnarchiver to convert NSData back to the object.

这有点麻烦，因为我每次都需要与 NSData 进行转换，但它确实有效.

It is a little cumbersome, because i need to convert to/from NSData everytime, but it just works.

以下是每个请求的一个示例:

Here is one example per request:

保存:

NSUserDefaults *defaults = [NSUserDefaults standardUserDefaults];
NSMutableArray *arr = ... ; // set value
NSData *data = [NSKeyedArchiver archivedDataWithRootObject:arr];
[defaults setObject:data forKey:@"theKey"];
[defaults synchronize];

加载:

NSUserDefaults *defaults = [NSUserDefaults standardUserDefaults];
NSData *data = [defaults objectForKey:@"theKey"];
NSArray *arr = [NSKeyedUnarchiver unarchiveObjectWithData:data];

数组中的元素实现

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

然后在CommentItem的实现中，提供了两个方法:

Then in the implementation of CommentItem, provides two methods:

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

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

谁有更好的解决方案?

谢谢大家.

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