swift - viewDidLoad 之前和之后的区别

Question

我尝试将 searchBar 设置为 viewDidLoad 内的 tableHeaderView:

 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()

}

这是我的 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 {}

}

但我不明白它们是行不通的。 Xcode 崩溃了，实际上什么也没有发生。然后我尝试更改 viewDidLoad 方法中的某些内容:

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



}

成功了!工作正常。我不明白有什么区别？

Answer 1

您应该尝试从 viewDidLoad() 方法中删除 self.tableView.reloadData()，因为数据甚至没有加载到重新加载。