filter NSFetchedResultsController result swift 2

Question

I want automatic updates on tableview..For that i have used NSFetchedResultsControlleras

lazy var fetchedResultsController: NSFetchedResultsController = {
    // Initialize Fetch Request
    let fetchRequest = NSFetchRequest(entityName: "Student")

    // Add Sort Descriptors
    let sortDescriptor = NSSortDescriptor(key: "grade", ascending: true)
    fetchRequest.sortDescriptors = [sortDescriptor]

    // Initialize Fetched Results Controller
    let fetchedResultsController = NSFetchedResultsController(fetchRequest: fetchRequest, managedObjectContext: self.managedObjectContext, sectionNameKeyPath: nil, cacheName: nil)

    // Configure Fetched Results Controller
    fetchedResultsController.delegate = self

    return fetchedResultsController
}()

But i have to filter the results after loading as of user selection as..

  @IBAction func onSegmentValueChanged(sender: UISegmentedControl)
    {
        if sender.selectedSegmentIndex == 0{

            //filter by grade
            let fetchRequest = NSFetchRequest(entityName: "Student")
            let sortDescriptor = NSSortDescriptor(key: "grade", ascending: true)
            fetchRequest.sortDescriptors = [sortDescriptor]
            let filterfetchResultsController = NSFetchedResultsController(fetchRequest: fetchRequest, managedObjectContext: self.managedObjectContext, sectionNameKeyPath: nil, cacheName: nil)
            let predicate = NSPredicate(format: "address = %@","Russia")
            filterfetchResultsController.fetchRequest.predicate = predicate
            self.tableView.reloadData()

        }else{

            let fetchRequest = NSFetchRequest(entityName: "Student")
            let sortDescriptor = NSSortDescriptor(key: "grade", ascending: true)
            fetchRequest.sortDescriptors = [sortDescriptor]
            let filterfetchResultsController = NSFetchedResultsController(fetchRequest: fetchRequest, managedObjectContext: self.managedObjectContext, sectionNameKeyPath: nil, cacheName: nil)
            let predicate = NSPredicate(format: "grade = %d",10)
            filterfetchResultsController.fetchRequest.predicate = predicate
            self.tableView.reloadData()


        }

    }

This however reload the tableView but data is not filtered.how do i solve this problem?This is the demo project i am working on.Or should i use the normal way passing the results and reloading tableView as of normal way to solve this problem?

Answer 1

1. You must use self.fetchedResultsController, this is your datasource, not filterfetchResultsController: there´s no connection.
2. You must do a performFetch() to execute the changed predicates

This works for me:

@IBAction func onSegmentValueChanged(sender: UISegmentedControl)
{
    if sender.selectedSegmentIndex == 1{

        //filter by address
        let predicate = NSPredicate(format: "address == %@","Russia")
        self.fetchedResultsController.fetchRequest.predicate = predicate

    }else{

        let predicate = NSPredicate(format: "grade = %d",10)
        self.fetchedResultsController.fetchRequest.predicate = predicate

    }

    do {
        try self.fetchedResultsController.performFetch()
    } catch {
        let fetchError = error as NSError
        print("\(fetchError), \(fetchError.userInfo)")
    }
    self.tableView.reloadData()

}