filter NSFetchedResultsController result swift 2 - ios

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

You must use self.fetchedResultsController, this is your datasource, not filterfetchResultsController: there´s no connection.
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()
}