我有一个核心数据应用程序。我想获取一种对象,User
. User
有财产userId
。
我有另一个数组userId
s, [1, 4, 3, 5]
。我想创建一个根据数组中 s的顺序对NSSortDescriptor
我的User
对象进行排序的方法。userId
这可能吗,我该怎么做?
更新
我现在尝试了以下方法。
我向我的 User 对象添加了一个可转换的属性,我在其中存储了用户 ids 数组。
我尝试了以下排序描述符:
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; }];
我收到以下错误:
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.'
更新 2
还想添加对象Followers
之间的关系。User
任何想法应该如何看待这种关系?见附图。那是对的吗?