NSSortDescriptor - 基于另一个数组排序描述符 [英] NSSortDescriptor - Sort descriptor based on another array

问题描述

我有一个核心数据应用程序。我想要获取一种对象， User 。 用户有属性 userId 。

我有另一个数组 userId s， [1，4，3，5 ] 。我想创建一个 NSSortDescriptor ，它根据用户对象> userId s。

这是否可能，我该怎么办？

更新

1. 我为User对象添加了一个transformable属性，用于存储用户id数组。




2. 我尝试了以下排序描述符：

     sortDescriptor = [[NSSortDescriptor alloc] initWithKey：@userIdascending：YES comparator：^ NSComparisonResult（id obj1，id obj2）{
    NSUInteger idx1 = [self.user.followingIds indexOfObject：[obj1 valueForKey：@userId ]]; 
    NSUInteger idx2 = [self.user.followingIds indexOfObject：[obj2 valueForKey：@userId]]; 
    return idx1  -  idx2; 
   }]; 
     

 严重的应用程序错误。在核心数据更改处理期间捕获异常。这通常是NSManagedObjectContextObjectsDidChangeNotification的观察器中的错误。 [< __ NSCFNumber 0xa337400> valueForUndefinedKey：]：此类不是关键值userId的键值编码兼容。 with userInfo {
 NSTargetObjectUserInfoKey = 2502; 
 NSUnknownUserInfoKey = userId; 
} 
 ***由于未捕获异常NSUnknownKeyException而终止应用程序，原因：'[< __ NSCFNumber 0xa337400> valueForUndefinedKey：]：此类不是键值编码符合关键userId。'
  

Update 2 用户对象。任何想法如何关系应该看起来？见附图。那是对的吗？

>

解决方案

这不能使用排序描述符，您必须在获取结果后应用自定义比较函数：

  NSArray * userIds = ...; //例如@ [@ 1，@ 4，@ 3，@ 5] 
 NSArray * results = ...; //获取请求的结果
 NSArray * sorted = [results sortedArrayUsingComparator：^ NSComparisonResult（id obj1，id obj2）{
 NSUInteger idx1 = [userIds indexOfObject：[obj1 valueForKey：@userId]]; 
 NSUInteger idx2 = [userIds indexOfObject：[obj2 valueForKey：@userId]]; 
 return idx1  -  idx2; 
}]; 
  

I hava a core data application. And I want to fetch one kind of object, User. User have the property userId.

I have another array with userIds, [1, 4, 3, 5]. And I would like to create a NSSortDescriptor that sorts my Userobjects based on the order of the userIds in the array.

Is that possible, and how should I do that?

Update

I have now tried the following.

1. I added a transformable property to my User object, where I store the user ids array.

2. I have tried the following sort descriptor:

   sortDescriptor = [[NSSortDescriptor alloc] initWithKey:@"userId" ascending:YES     comparator:^NSComparisonResult(id obj1, id obj2) {
       NSUInteger idx1 = [self.user.followingIds indexOfObject:[obj1 valueForKey:@"userId"]];
       NSUInteger idx2 = [self.user.followingIds indexOfObject:[obj2 valueForKey:@"userId"]];
       return idx1 - idx2;
   }];
   

And I'm getting the following error:

Serious application error.  Exception was caught during Core Data change processing.  This  is usually a bug within an observer of NSManagedObjectContextObjectsDidChangeNotification.   [<__NSCFNumber 0xa337400> valueForUndefinedKey:]: this class is not key value coding-compliant  for the key userId. with userInfo {
    NSTargetObjectUserInfoKey = 2502;
    NSUnknownUserInfoKey = userId;
}
*** Terminating app due to uncaught exception 'NSUnknownKeyException', reason:    '[<__NSCFNumber 0xa337400> valueForUndefinedKey:]: this class is not key value coding-   compliant for the key userId.'

Update 2

Would also like to add a relationship Followers between User objects. Any ideas how that relationship should look? See attached image. Is that correct?

解决方案

This can not be done with a sort descriptor, you have to apply a custom comparator function after fetching the results:

NSArray *userIds = ...; // e.g. @[@1, @4, @3, @5]
NSArray *results = ...; // result of fetch request
NSArray *sorted = [results sortedArrayUsingComparator:^NSComparisonResult(id obj1, id obj2) {
    NSUInteger idx1 = [userIds indexOfObject:[obj1 valueForKey:@"userId"]];
    NSUInteger idx2 = [userIds indexOfObject:[obj2 valueForKey:@"userId"]];
    return idx1 - idx2;
}];

这篇关于NSSortDescriptor - 基于另一个数组排序描述符的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！