override func viewDidLoad() {
    super.viewDidLoad()
 
 
    // SearchController initializiation
    self.searchController = UISearchController.init(searchResultsController: nil)
    self.searchController.delegate = self
    self.searchController.searchBar.delegate = self
    self.searchController.searchBar.sizeToFit()
    self.searchController.searchResultsUpdater = self
    self.searchController.searchBar.barTintColor = UIColor.white
    self.searchController.searchBar.keyboardAppearance = .default
    self.searchController.searchBar.backgroundColor = UIColor.white
    self.searchController.hidesNavigationBarDuringPresentation = true
    self.searchController.obscuresBackgroundDuringPresentation = false
 
 
    self.tableView.tableHeaderView = self.searchController.searchBar
    self.definesPresentationContext = true
 
    self.fetch()
    self.tableView.reloadData()
 
}

这个我的fetch()函数：

func fetch() {
    let fetchRequest:NSFetchRequest<Phone> = Phone.fetchRequest()
    fetchRequest.sortDescriptors = [NSSortDescriptor.init(key: "header",ascending: true),NSSortDescriptor.init(key: "date",ascending: true)]
 
    self.fetchedResultsController = NSFetchedResultsController.init(fetchRequest: fetchRequest,managedObjectContext: self.managedObjectContext,sectionNameKeyPath: "header",cacheName: nil)
    self.fetchedResultsController.delegate = self
 
    do {
        try self.fetchedResultsController.performFetch()
        self.tableView.reloadData()
    } catch {}
 
}

但我不明白他们是不会工作的. Xcode崩溃,实际上没有发生.然后我尝试改变viewDidLoad里面的内容：

override func viewDidLoad() {
    super.viewDidLoad()
 
    self.fetch()
    self.tableView.reloadData()
 
    // SearchController initializiation
    self.searchController = UISearchController.init(searchResultsController: nil)
    self.searchController.delegate = self
    self.searchController.searchBar.delegate = self
    self.searchController.searchBar.sizeToFit()
    self.searchController.searchResultsUpdater = self
    self.searchController.searchBar.barTintColor = UIColor.white
    self.searchController.searchBar.keyboardAppearance = .default
    self.searchController.searchBar.backgroundColor = UIColor.white
    self.searchController.hidesNavigationBarDuringPresentation = true
    self.searchController.obscuresBackgroundDuringPresentation = false
 
 
    self.tableView.tableHeaderView = self.searchController.searchBar
    self.definesPresentationContext = true
 
 
 
}

成功！工作正常我不明白有什么区别？