如何过滤在 Core Data 中有对象的表视图？

Question

我正在创建一个联系人应用程序，到目前为止，我已经成功地将项目保存到我的 tableview 中。我有一个搜索栏，我想按名字过滤掉我的单元格，我知道因为我在核心数据中工作，所以我必须使用 fetchResultsController 和 NSPredicate。我很难弄清楚这些东西，也许有人可以帮助我？

这也是我的核心数据实体，以防万一。

实体：联系人

属性：

• 名字，字符串
• 姓氏，字符串
• 出生日期，字符串
• 电话号码，字符串
• 邮政编码，字符串

我知道有些代码可能不完整，但我只需要指导如何使用它。我只想让用户输入一个名字，它会按名字过滤单元格。如果您需要更多信息，请告诉我。

现在这是我的 ContactsTableVC 中的代码：

import UIKit
import CoreData

class ContactsTableVC: UITableViewController, UISearchBarDelegate, NSFetchedResultsControllerDelegate {

    @IBOutlet weak var searchBar: UISearchBar!

    var isFiltered: Bool = false

//Holds the core data model
    var persons: [Person] = []

    override func viewDidLoad() {
        super.viewDidLoad()

        searchBar.delegate = self

        self.tableView.separatorStyle = UITableViewCellSeparatorStyle.none
        self.tableView.backgroundColor = UIColor(red: 240/255.0, green: 240/255.0, blue: 240/255.0, alpha: 1.0)

        fetch()
        self.tableView.reloadData()
    }

    func getContext () -> NSManagedObjectContext {
        let appDelegate = UIApplication.shared.delegate as! AppDelegate
        return appDelegate.persistentContainer.viewContext
    }

    // MARK: - Searchbar
    //add fetchrequest to did ebgin editing
    func searchBarTextDidBeginEditing(_ searchBar: UISearchBar) {

    }

    func searchBarTextDidEndEditing(_ searchBar: UISearchBar) {
        if(searchBar.text == "") {
            isFiltered = false
        } else {
            isFiltered = true
        }
    }

    func searchBar(_ searchBar: UISearchBar, textDidChange searchText: String) {
        filter(text: searchText)
    }

    // MARK: - Fetchresults controller / filtering data

    func filter(text: String) {
        //Create fetch request
        let fetchRequest = NSFetchRequest<Person>()

//        guard let appDelegate = UIApplication.shared.delegate as? AppDelegate else { return }         replaced with getcontext
//        let managedObjectContext = appDelegate.persistentContainer.viewContext

        let entity = NSEntityDescription.entity(forEntityName: "Contact", in: getContext())
        fetchRequest.entity = entity

        let sortDescriptor = NSSortDescriptor(key: "firstName", ascending: false)
        let sortDescriptors: [Any] = [sortDescriptor]
        fetchRequest.sortDescriptors = sortDescriptors as? [NSSortDescriptor] ?? [NSSortDescriptor]()

        if(text.characters.count > 0) {
            let predicate = NSPredicate(format: "(firstName CONTAINS[c] %@)", text)
            fetchRequest.predicate = predicate
        }

        let loadedEntities: [Person]? = try? getContext().fetch(fetchRequest)
        filteredContacts = [Any](arrayLiteral: loadedEntities) as! [Person]
        self.tableView.reloadData()
    }

    // MARK: - Data Source
    func fetch() {
        guard let appDelegate = UIApplication.shared.delegate as? AppDelegate else { return }
        let managedObjectContext = appDelegate.persistentContainer.viewContext
        let fetchRequest = NSFetchRequest<NSFetchRequestResult>(entityName:"Contact")
        do {
            persons = try managedObjectContext.fetch(fetchRequest) as! [Person] //NSManagedObject
        } catch let error as NSError {
            print("Could not fetch. \(error)")
        }
    }

    func save(firstName: String, lastName: String, dob: String, phoneNumber: String, zipCode: String) {
        guard let appDelegate = UIApplication.shared.delegate as? AppDelegate else { return }
        let managedObjectContext = appDelegate.persistentContainer.viewContext
        guard let entity = NSEntityDescription.entity(forEntityName:"Contact", in: managedObjectContext) else { return }
        let person = NSManagedObject(entity: entity, insertInto: managedObjectContext)
        person.setValue(firstName, forKey: "firstName")
        person.setValue(lastName, forKey: "lastName")
        person.setValue(dob, forKey: "dateOfBirth")
        person.setValue(phoneNumber, forKey: "phoneNumber")
        person.setValue(zipCode, forKey: "zipCode")
        do {
            try managedObjectContext.save()
            self.persons.append(person as! Person) //previously just contact, no casting!
        } catch let error as NSError {
            print("Couldn't save. \(error)")
        }
    }

    func update(indexPath: IndexPath, firstName: String, lastName: String, dob: String, phoneNumber: String, zipCode: String) {
        guard let appDelegate = UIApplication.shared.delegate as? AppDelegate else { return }
        let managedObjectContext = appDelegate.persistentContainer.viewContext
        let contact = persons[indexPath.row]
        contact.setValue(firstName, forKey: "firstName")
        contact.setValue(lastName, forKey: "lastName")
        contact.setValue(dob, forKey: "dateOfBirth")
        contact.setValue(phoneNumber, forKey: "phoneNumber")
        contact.setValue(zipCode, forKey: "zipCode")
        do {
            try managedObjectContext.save()
            persons[indexPath.row] = contact
        } catch let error as NSError {
            print("Couldn't update. \(error)")
        }
    }

    func delete(_ contact: NSManagedObject, at indexPath: IndexPath) {
        guard let appDelegate = UIApplication.shared.delegate as? AppDelegate else { return }
        let managedObjectContext = appDelegate.persistentContainer.viewContext
        managedObjectContext.delete(contact)
        persons.remove(at: indexPath.row)

        //Always remember to save after deleting, updates Core Data
        do {
            try managedObjectContext.save()
        } catch {
            print("Something went wrong \(error.localizedDescription)")
        }
    }

    // MARK: - Table View Setup
    override func numberOfSections(in tableView: UITableView) -> Int {
        return 1
    }

    override func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
        return persons.count
    }


    override func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
        let cell = tableView.dequeueReusableCell(withIdentifier: "ContactCell", for: indexPath) as? PersonsCell

        let person = persons[indexPath.row]

        cell?.firstName?.text = person.value(forKey:"firstName") as? String
        cell?.lastName?.text = person.value(forKey:"lastName") as? String
        cell?.dob?.text = person.value(forKey:"dateOfBirth") as? String
        cell?.phoneNumber?.text = person.value(forKey:"phoneNumber") as? String
        cell?.zipCode?.text = person.value(forKey:"zipCode") as? String

        return cell!
    }

    override func tableView(_ tableView: UITableView, heightForRowAt indexPath: IndexPath) -> CGFloat {
        return 75
    }

    // Override to support conditional editing of the table view.
    override func tableView(_ tableView: UITableView, canEditRowAt indexPath: IndexPath) -> Bool {
        return true
    }

    // MARK: - Navigation
    @IBAction func unwindToContactsList(segue:UIStoryboardSegue) {
        if let viewController = segue.source as? AddContactVC {
            guard let _firstName: String = viewController.firstNameLbl.text,
                let _lastName: String = viewController.lastNameLbl.text,
                let _dob: String = viewController.dateOfBirthLbl.text,
                let _phoneNumber: String = viewController.phoneNumberLbl.text,
                let _zipCode: String = viewController.zipCodeLbl.text
                else { return }
            if _firstName != "" && _lastName != "" && _dob != "" && _phoneNumber != "" && _zipCode != "" {
                if let indexPath = viewController.indexPathForContact {
                    update(indexPath: indexPath, firstName: _firstName, lastName: _lastName, dob: _dob, phoneNumber: _phoneNumber, zipCode: _zipCode)
                    print("Any updates?")
                } else {
                    save(firstName: _firstName, lastName: _lastName, dob: _dob, phoneNumber: _phoneNumber, zipCode: _zipCode)
                    print("added to tableview") //this runs twice for some reason...
                }
            }
            tableView.reloadData()
        } else if let viewController = segue.source as? EditContactVC {
            if viewController.isDeleted {
                guard let indexPath: IndexPath = viewController.indexPath else { return }
                let person = persons[indexPath.row]
                delete(person, at: indexPath)
                tableView.reloadData()
            }
        }
    }
}

Answer 1

这里是使用NSFetchedResultsController 实现目标的示例代码。我省略了一些不相关的代码。

class ContactViewController: UITableViewController {
    let fetchedResultsController: NSFetchedResultsController<Contact>!

    func searchTextFieldDidEditingChanged(_ textField: UITextField) {
        let text = textField.text ?? ""
        refetch(with: text)
    }

    // The key is you need change the predicate when searchTextField's 
    // value changed, and invoke proformFetch() again
    func refetch(with text: String) {
        let predicate = NSPredicate(format: "firstName CONTAINS %@", text)
        fetchedResultsController.fetchRequest.predicate = predicate

        do {
            try self.fetchedResultsController.performFetch()
            tableView.reloadData()
        } catch let error as NSError {
            loggingPrint("Error: \(error.localizedDescription)")
        }
    }
}

// MARK: - Table datasource

extension ContactViewController {
    override func numberOfSections(in tableView: UITableView) -> Int {
        return fetchedResultsController.sections!.count
    }

    override func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
        let sectionInfo = fetchedResultsController.sections![section]
        return sectionInfo.numberOfObjects
    }

    override func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
        let cell = tableView.dequeueReusableCell(withIdentifier: "ContactCell", for: indexPath) as? PersonsCell

        let contact = fetchedResultsController.object(at: indexPath)
        cell.contact = contact

        return cell!
    }
}

Answer 2

您可以使用 NSPredicate 的sortDescriptors 属性来过滤获取请求的结果。

查看链接了解更多信息： How to sort a fetch in Core Data