NSFetchedResultsController ，其中包含由字符串的第一个字母创建的部分

使用NSFetchedResultsController来创建分段文章

swift
import UIKit
import CoreData
class ViewController: UIViewController, UITableViewDataSource, NSFetchedResultsControllerDelegate {
    @IBOutlet weak var tableView: UITableView!
    
    var fetchedResultsController: NSFetchedResultsController!
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
        // 设置NSFetchedResultsController
        let fetchRequest = NSFetchRequest(entityName: "Article")
        let sortDescriptor = NSSortDescriptor(key: "title", ascending: true)
        fetchRequest.sortDescriptors = [sortDescriptor]
        
        fetchedResultsController = NSFetchedResultsController(fetchRequest: fetchRequest, managedObjectContext: AppDelegate.shared.persistentContainer.viewContext, sectionNameKeyPath: "titleFirstLetter", cacheName: nil)
        fetchedResultsController.delegate = self
        
        do {
            try fetchedResultsController.performFetch()
        } catch {
            print("Fetch failed")
        }
    }
    
    // UITableViewDataSource方法
    func numberOfSections(in tableView: UITableView) -> Int {
        return fetchedResultsController.sections?.count ?? 0
    }
    
    func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
        guard let sections = fetchedResultsController.sections else {
            return 0
        }
        let sectionInfo = sections[section]
        return sectionInfo.numberOfObjects
    }
    
    func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
        let cell = tableView.dequeueReusableCell(withIdentifier: "Cell", for: indexPath)
        
        let article = fetchedResultsController.object(at: indexPath)
        cell.textLabel?.text = article.value(forKey: "title") as? String
        
        return cell
    }
    
    // NSFetchedResultsControllerDelegate方法
    func controllerDidChangeContent(_ controller: NSFetchedResultsController) {
        tableView.reloadData()
    }
}