viewDidLoad

Question

我尝试将searchBar设置为tableHeaderView内的viewDidLoad：

 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()功能：

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 {}

}

但我不明白他们没有工作。 Xcode崩溃，实际上什么都没发生。然后我试图改变viewDidLoad方法中的内容：

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？

Answer 1

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

Answer 2

这是因为你甚至在初始化fetchedResultsController之前设置了searchResultsUpdater和searchBar的委托。在您的代码searchResultsUpdater或searchBar的委托方法中的某些位置正在访问您的fetchedResultsController并将其设置为nil，以便您应用程序崩溃。我的建议是避免崩溃是使searchResultsController成为计算或惰性属性。