UISearchController中的UITextField成为FirstResponder

Question

我在UISearchController中有一个UITextField，当显示视图控制器时，它需要成为FirstResponder。

在ViewDidLoad上构建UISearchController。

在ViewDidAppear上，我从UISearchController获取UITextField并告诉它成为BeginFirstResponder

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永远不会成为第一响应者，因为它不能成为第一响应者。 为什么UITextField不能成为第一个响应者？

Answer 1

视图控制器将其视图层次结构加载到内存中但未呈现给用户之后，将调用ViewDidLoad 。 您不能在该阶段与对象执行UI交互。

UISearchController具有一个委托方法，该方法在自动显示后会被调用。 用它调出键盘。

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