swift - 如何在后台线程中加载核心数据

Question

我的核心数据存储中有一些大数据我如何在后台线程中加载这些数据？

    func connectionCoreData() {
        let fetchRequest = NSFetchRequest<PersonalClass>(entityName: "PersonalBase")
        let sortDescriptor = NSSortDescriptor(key: "personName", ascending: true)
        fetchRequest.sortDescriptors = [sortDescriptor]
        if let managerObjectContext = (UIApplication.shared.delegate as? AppDelegate)?.managedObjectContext {
            fetchResultController = NSFetchedResultsController(fetchRequest: fetchRequest, managedObjectContext: managerObjectContext, sectionNameKeyPath: nil, cacheName: nil)
            fetchResultController.delegate = self
            do {
                try fetchResultController.performFetch()
                personalArray = fetchResultController.fetchedObjects!
                self.tableView.reloadData()
            } catch {
                print(error)
            }
        }
    }

我需要在后台线程中添加核心数据加载，然后更新我的 tableView

Answer 1

首先，您应该记住 managedObjectContext 在单个线程上运行。您应该在同一个线程上访问/编辑加载的对象。

在您的情况下，您将与要在主线程上加载的对象进行交互。例如，加载的数据库对象将填充一个 tableView，这应该在主线程上完成。这会强制 managedObjectContext 成为在主线程上运行的 MainContextType。

http://developer.apple.com/library/ios/#documentation/cocoa/conceptual/CoreData/Articles/cdConcurrency.html

您不应该害怕在主线程上运行 NSFetchedResultsController，因为它会批量加载对象。但是，您没有按应有的方式使用 FetchedResults Controller 。你的代码中不应该有这两行。

personalArray = fetchResultController.fetchedObjects!
self.tableView.reloadData()

您应该使用此方法访问加载的对象 fetchResultController .objectAtIndexPath(indexPath)。

这是一个如何使用 NSFetchedResultsController

的例子

class ViewController: UITableViewController NSFetchedResultsControllerDelegate{

    lazy var fetchedResultsController: NSFetchedResultsController = {
        let fetchRequest = ... //Create the fetch request
        let sortDescriptor = ... //Create a sortDescriptor
        let predicate = ...//Create the predicate if you want to filter the results
        fetchRequest.predicate = predicate

        let fetchedResultsController = NSFetchedResultsController(fetchRequest: fetchRequest, managedObjectContext: mainContext, sectionNameKeyPath: nil, cacheName: nil)
        fetchedResultsController.delegate = self
        return fetchedResultsController
    }()

    override fun viewDidLoad(){
         super.viewDidLoad()
         do {
             try self.fetchedResultsController.performFetch()
         }catch {
             print(error)
         }
    }

    func controllerWillChangeContent(controller: NSFetchedResultsController) {
        tableView.beginUpdates()
    }

    func controllerDidChangeContent(controller: NSFetchedResultsController) {
        tableView.endUpdates()
    }

    func controller(controller: NSFetchedResultsController, didChangeObject anObject: AnyObject, atIndexPath indexPath: NSIndexPath?, forChangeType type: NSFetchedResultsChangeType, newIndexPath: NSIndexPath?) {
        switch (type) {
        case .Insert:
            if let indexPath = newIndexPath {
                tableView.insertRowsAtIndexPaths([indexPath], withRowAnimation: .Fade)
            }
            break;
        case .Delete:
            if let indexPath = indexPath {
                tableView.deleteRowsAtIndexPaths([indexPath], withRowAnimation: .Fade)
            }
            break;
        case .Update:
            if let indexPath = indexPath {
                tableView.reloadRowsAtIndexPaths([indexPath], withRowAnimation: .Automatic)
            }
            break;
        case .Move:
            if let indexPath = indexPath, newIndexPath = newIndexPath {
                tableView.moveRowAtIndexPath(indexPath, toIndexPath: newIndexPath)
            }
            break;
        }
    }
    override func tableView(tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
        if let sections = fetchedResultsController.sections {
            let sectionInfo = sections[section]
            return sectionInfo.numberOfObjects
        }
        return 0
    }

   override func tableView(tableView: UITableView, cellForRowAtIndexPath indexPath: NSIndexPath) -> UITableViewCell {
       let obj = fetchedResultsController.objectAtIndexPath(indexPath){
       ....
    }

}