UITextField in UISearchController BecomeFirstResponder

Question

我有一个UITextField，它位于视图控制器显示时需要成为FirstResponder的UISearchController中。

在ViewDidLoad上构建了UISearchController。

在ViewDidAppear上，我从UISearchController得到UITextField并告诉BecomeFirstResponder

public override void ViewDidLoad(bool animated)
    {
        base.ViewDidLoad();
        BuildSearchController();

        SearchController.SearchBar.BecomeFirstResponder();
    }

private void BuildSearchController()
    {
        UIFont MyFont = UIFont.FromName("Helvetica", 20f);

        SearchController = new UISearchController(ResultsTableController)
        {
            WeakDelegate = this,
            DimsBackgroundDuringPresentation = false,
            WeakSearchResultsUpdater = this,
        };

        SearchController.SearchBar.ScopeButtonTitles = new string[5] { "Account", "Name", "Service Address", "Phone", "SSN" };
        UITextField SearchField = (UITextField)SearchController.SearchBar.Subviews[0].Subviews[2];

        SearchField.Font = MyFont;
        SearchController.SearchBar.ShowsCancelButton = false;
        SearchController.SearchBar.SetScopeBarButtonTitle(new UITextAttributes() { Font = MyFont }, UIControlState.Normal);
        SearchController.SearchBar.SizeToFit();
        SearchController.SearchBar.SelectedScopeButtonIndex = 1;
        SearchController.SearchBar.SetShowsCancelButton(false, false);

        UISegmentedControl TempSegControl = SearchController.SearchBar.Subviews[0].Subviews[0].Subviews[1] as UISegmentedControl;
        TempSegControl.BackgroundColor = UIColor.FromRGBA(0, 122, 255, 255);
        TempSegControl.TintColor = UIColor.White;
        TempSegControl.Layer.BorderWidth = 1;
        TempSegControl.Layer.CornerRadius = 6;
        TempSegControl.Layer.BorderColor = UIColor.White.CGColor;
        SearchController.SearchBar.BarTintColor = UIColor.FromRGBA(232, 232, 232, 255);


        SearchController.HidesNavigationBarDuringPresentation = false;

        SearchField.BecomeFirstResponder();
        TableView.TableHeaderView = SearchController.SearchBar;

        SearchController.SearchBar.WeakDelegate = this;
    }

public override void ViewDidAppear(bool animated)
    {
        UITextField SearchBox = SearchController.SearchBar.Subviews[0].Subviews[2] as UITextField;

        if (SearchBox.CanBecomeFirstResponder)
        {
            SearchBox.BecomeFirstResponder();
        }
        base.ViewWillAppear(animated);
    }

UITextField永远不会成为第一个响应者，因为它不能成为第一个响应者。为什么UITextField不能成为第一个修复器？

Answer 1

ViewDidLoad是在视图控制器将其视图层次结构加载到内存但未显示给用户之后调用的。在这个阶段，您不能与对象执行UI交互。

UISearchController有一个委托方法，该方法在自动显示时被调用。用它打开键盘。

optional func didPresentSearchController(searchController: UISearchController){
        searchController.searchBar.becomeFirstResponder();
    }