如何在应用程序的plist文件中存储提取结果？

Question

我使用Fetch查询sqlite数据库中的行，并将结果加载到NSMutableArray myDataArray中。我想要做的是将myDataArray中的值存储到我的应用程序的首选项plist文件中。但是，当我运行下面的代码，我得到以下错误：

[NSUserDefaults的方法setObject：forKey：]：尝试插入非财产价值“（ ...（注：包含50个行值） ）”类'__NSArrayM'。

我使用相同的方法在我的plist文件中存储其他NSMutableArrays，但无法找出存储查询的数据库结果的方法。

您可能会问：为什么要存储这些值，只是在需要再次查询数据库时重新查询数据库？原因是我从数据库中随机抽取了行，我需要回忆这些行与它们最初的随机数。

任何帮助表示赞赏， LQ

... 
fetchResults = [managedObjectContext executeFetchRequest:request error:&error]; 
self.myDataArray = [NSMutableArray arrayWithArray:fetchResults]; 

NSUserDefaults *userDefaults = [NSUserDefaults standardUserDefaults]; 
[userDefaults setObject:self.myDataArray forKey:kFetchResultsArray]; 

Answer 1

在myDataArray的项目是不是属性列表对象，所以它们不能被自动序列化到一个plist中。

从NSUserDefaults class reference为setObject:forKey:：

The value parameter can be only property list objects: NSData, NSString, NSNumber, NSDate, NSArray, or NSDictionary. For NSArray and NSDictionary objects, their contents must be property list objects. See “What is a Property List?” in Property List Programming Guide.

你可能要考虑比用户默认存储该数据的其它机制。来自Property List Programming Guide：

Many applications require a mechanism for storing information that will be needed at a later time. For situations where you need to store small amounts of persistent data—say less than a few hundred kilobytes—property lists offer a uniform and convenient means of organizing, storing, and accessing the data.

In some situations, the property-list architecture may prove insufficient. If you need a way to store large, complex graphs of objects, objects not supported by the property-list architecture, or objects whose mutability settings must be retained, use archiving. See Archives and Serializations Programming Guide for more information.