启动Core Data应用程序时在后台配置NSFetchedResultsController [英] Configure NSFetchedResultsController in background when launching Core Data app

问题描述

 我已经设置一个Core Data应用程序与通常的样板代码，并且RootViewController通过调用这个初始化FRC： - （NSFetchedResultsController *）fetchedResultsController 
 {
 if（__fetchedResultsController！= nil）
 {
 return __fetchedResultsController; 
} 
 //配置fetchRequest，sectionKey和cacheName 
 __fetchedResultsController = [[NSFetchedResultsController alloc] initWithFetchRequest：fetchRequest 
 managedObjectContext：self.managedObjectContext 
 sectionNameKeyPath：sectionKey 
 cacheName：cacheName]; 
 return __fetchedResultsController; 
} 
  

我看到的所有示例代码都是这样。然而，我有一个大的数据集和超过15,000条目，需要大约5秒钟在iPhone 4S上启动的应用程序。这是与缓存启用（没有它，它需要11秒），并与索引的属性。

所以我想能够显示一个 UIActivityIndi​​catorView ，应用程式正在等待载入。我知道如何通常在后台线程中加载核心数据对象，然后将它们合并回主线程，但是如何在后台线程中初始化FRC，以便在后台加载和分段所有对象？

我知道我可以加载所有对象，并在后台线程中将它们分割成自定义字典，并使用它来呈现数据，但我宁愿使用标准FRC呼叫和代表。

感谢。

解决方案

我想我想...你可以在后台线程中创建FRC并在主线程中执行fetch：

   - （NSFetchedResultsController *） fetchedResultsController 
 {
 if（__fetchedResultsController！= nil）
 {
 return __fetchedResultsController; 
} 
 
 //创建一些东西传回第一次FRC被初始化而不提取
 __block NSFetchedResultsController * aFetchedResultsController = [[NSFetchedResultsController alloc] initWithFetchRequest：fetchRequest managedObjectContext：self。 managedObjectContext sectionNameKeyPath：nil cacheName：nil]; 
 aFetchedResultsController.delegate = self; 
 [self.list_spinner startAnimating]; 
 
 dispatch_async（self.filterMainQueue，^ {
 
 NSFetchedResultsController * newFetchedResultsController = [[NSFetchedResultsController alloc] initWithFetchRequest：fetchRequest 
 managedObjectContext：self.managedObjectContext 
 sectionNameKeyPath ：sectionKey 
 cacheName：cacheName]; 
 dispatch_async（dispatch_get_main_queue（），^ {
 // stop the spinner here 
 [self.list_spinner stopAnimating]; 
 
 NSError * error = nil; 
 if（！[newFetchedResultsController performFetch：& error]）
 {
 NSLog（@未解析的错误％@，％@，错误，[错误userInfo]）; 
 [SimpleListAppDelegate showCoreDataError：@SimpleListViewController  -  FRC]; 
} 
 __fetchedResultsController = nil; 
 newFetchedResultsController.delegate = self; 
 __fetchedResultsController = newFetchedResultsController; 
 [self.tableView reloadData]; 
}）; 
}）; 
 
 return aFetchedResultsController; 
} 
  

I have setup a Core Data app with the usual boilerplate code, and the RootViewController initializes the FRC by calling this:

- (NSFetchedResultsController *)fetchedResultsController 
{
    if (__fetchedResultsController != nil) 
    {
        return __fetchedResultsController;
    }
    // configure the fetchRequest, sectionKey and cacheName
    __fetchedResultsController = [[NSFetchedResultsController alloc] initWithFetchRequest: fetchRequest 
                                                                    managedObjectContext: self.managedObjectContext 
                                                                      sectionNameKeyPath: sectionKey 
                                                                               cacheName: cacheName];
    return __fetchedResultsController;
}

All the sample code I've seen does this. However, I have a large data set and with over 15,000 entries, it takes about 5 seconds to launch the app on the iPhone 4S. This is with caching enabled (without it, it takes 11 seconds), and with indexed attributes.

So I want to be able to show a UIActivityIndicatorView which the app is waiting for this to load. I know how to generally load core data objects in the background thread and then merge them back into the main thread, but how can I initialize the FRC in the background thread so that all the objects are loaded and sectioned in the background?

I know I can load all the objects and partition them in a background thread into a custom dictionary and use that to present the data, but I would rather use the standard FRC calls and delegates.

Thanks.

解决方案

I think I've figured it out... you CAN create the FRC in the background thread and do the fetch in the main thread:

- (NSFetchedResultsController *)fetchedResultsController 
{
    if (__fetchedResultsController != nil) 
    {
        return __fetchedResultsController;
    }

    // create something to pass back to the first time FRC is initialized without fetching
    __block NSFetchedResultsController *aFetchedResultsController = [[NSFetchedResultsController alloc] initWithFetchRequest:fetchRequest managedObjectContext:self.managedObjectContext sectionNameKeyPath:nil cacheName:nil];
    aFetchedResultsController.delegate = self;
    [self.list_spinner startAnimating];

    dispatch_async(self.filterMainQueue, ^{

           NSFetchedResultsController *newFetchedResultsController = [[NSFetchedResultsController alloc] initWithFetchRequest: fetchRequest 
                                                                                                         managedObjectContext: self.managedObjectContext 
                                                                                                           sectionNameKeyPath: sectionKey 
                                                                                                                    cacheName: cacheName];
           dispatch_async(dispatch_get_main_queue(), ^{ 
               // stop the spinner here
               [self.list_spinner stopAnimating];

               NSError *error = nil;
               if (![newFetchedResultsController performFetch:&error]) 
               {
                   NSLog(@"Unresolved error %@, %@", error, [error userInfo]);
                   [SimpleListAppDelegate showCoreDataError: @"SimpleListViewController - FRC"];
               }
               __fetchedResultsController = nil;
               newFetchedResultsController.delegate = self;
               __fetchedResultsController = newFetchedResultsController;
               [self.tableView reloadData];
           });
         });

    return aFetchedResultsController;
}

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