viewDidLoad中之前和之后的区别

Question

我试图设置searchBar为tableHeaderView内部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 {}

}

但我不明白他们是不行的.Xcode崩溃,实际上什么都没发生.然后我试图改变viewDidLoad方法内部的东西:

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

这是因为您在 fetchedResultsController 初始化之前就设置了 searchResultsUpdater 和 searchBar 的委托。代码中的某些地方 searchResultsUpdater 或 searchBar 的委托方法正在访问您的 fetchedResultsController 并将其获取为零，因此应用程序崩溃。我的建议是避免崩溃，将 searchResultsController 设置为计算属性或惰性属性。