FrameworkElement.PredictFocus(FocusNavigationDirection) Metoda

Definicja

Określa następny element, który będzie miał fokus względem tego elementu dla podanego kierunku przenoszenia fokusu, ale nie przesuwa fokusu.Determines the next element that would receive focus relative to this element for a provided focus movement direction, but does not actually move the focus.

public:
 override System::Windows::DependencyObject ^ PredictFocus(System::Windows::Input::FocusNavigationDirection direction);
public override sealed System.Windows.DependencyObject PredictFocus (System.Windows.Input.FocusNavigationDirection direction);
override this.PredictFocus : System.Windows.Input.FocusNavigationDirection -> System.Windows.DependencyObject
Public Overrides NotOverridable Function PredictFocus (direction As FocusNavigationDirection) As DependencyObject

Parametry

direction
FocusNavigationDirection

Kierunek, dla którego należy określić potencjalną zmianę fokusu.The direction for which a prospective focus change should be determined.

Zwraca

Następny element, który koncentruje się na tym, jeśli fokus został rzeczywiście przesunięty.The next element that focus would move to if focus were actually traversed. Może zwracać null, jeśli fokus nie może zostać przeniesiony względem tego elementu w danym kierunku.May return null if focus cannot be moved relative to this element for the provided direction.

Wyjątki

Określono jeden z następujących kierunków w TraversalRequest: Next, Previous, First, Last.Specified one of the following directions in the TraversalRequest: Next, Previous, First, Last. Te wskazówki nie są prawne dla PredictFocus(FocusNavigationDirection) (ale są one dozwolone dla MoveFocus(TraversalRequest)).These directions are not legal for PredictFocus(FocusNavigationDirection) (but they are legal for MoveFocus(TraversalRequest)).

Przykłady

W poniższym przykładzie jest implementowana procedura obsługi, która obsługuje kilka możliwych wejść przycisku, każdy przycisk reprezentujący możliwą FocusNavigationDirection.The following example implements a handler that handles several possible button inputs, each button representing a possible FocusNavigationDirection. Program obsługi śledzi element z bieżącym fokusem klawiatury i wywołuje PredictFocus na tym elemencie i określa odpowiednie FocusNavigationDirection jako inicjalizację dla podanego parametru typu TraversalRequest.The handler tracks the element with current keyboard focus, and calls PredictFocus on that element, and specifies the appropriate FocusNavigationDirection as initialization for the TraversalRequest type parameter provided. Zamiast przechodzenia do tego elementu jako MoveFocus, program obsługi zmienia wymiary fizyczne przewidywanego miejsca docelowego fokusu na potrzeby wizualizacji.Instead of moving to that element as MoveFocus would do, the handler changes the physical dimensions of the predicted focus destination for visualization purposes.

    private void OnPredictFocus(object sender, RoutedEventArgs e)
    {
        DependencyObject predictionElement = null;

        UIElement elementWithFocus = Keyboard.FocusedElement as UIElement;

        if (elementWithFocus != null)
        {
            // Only these four directions are currently supported
            // by PredictFocus, so we need to filter on these only.
            if ((_focusMoveValue == FocusNavigationDirection.Up) ||
                (_focusMoveValue == FocusNavigationDirection.Down) ||
                (_focusMoveValue == FocusNavigationDirection.Left) ||
                (_focusMoveValue == FocusNavigationDirection.Right))
            {

                // Get the element which would receive focus if focus were changed.
                predictionElement = elementWithFocus.PredictFocus(_focusMoveValue);
               
                Control controlElement = predictionElement as Control;

                // If a ContentElement.
                if (controlElement != null)
                {
                    controlElement.Foreground = Brushes.DarkBlue;
                    controlElement.FontSize += 10;
                    controlElement.FontWeight = FontWeights.ExtraBold;

                    // Fields used to reset the UI when the mouse 
                    // button is released.
                    _focusPredicted = true;
                    _predictedControl = controlElement;
                }
            }
        }
    }
Private Sub OnPredictFocus(ByVal sender As Object, ByVal e As RoutedEventArgs)
    Dim predictionElement As DependencyObject = Nothing

    Dim elementWithFocus As UIElement = TryCast(Keyboard.FocusedElement, UIElement)

    If elementWithFocus IsNot Nothing Then
        ' Only these four directions are currently supported
        ' by PredictFocus, so we need to filter on these only.
        If (_focusMoveValue = FocusNavigationDirection.Up) OrElse (_focusMoveValue = FocusNavigationDirection.Down) OrElse (_focusMoveValue = FocusNavigationDirection.Left) OrElse (_focusMoveValue = FocusNavigationDirection.Right) Then

            ' Get the element which would receive focus if focus were changed.
            predictionElement = elementWithFocus.PredictFocus(_focusMoveValue)

            Dim controlElement As Control = TryCast(predictionElement, Control)

            ' If a ContentElement.
            If controlElement IsNot Nothing Then
                controlElement.Foreground = Brushes.DarkBlue
                controlElement.FontSize += 10
                controlElement.FontWeight = FontWeights.ExtraBold

                ' Fields used to reset the UI when the mouse 
                ' button is released.
                _focusPredicted = True
                _predictedControl = controlElement
            End If
        End If
    End If
End Sub

Uwagi

MoveFocus jest metodą powiązaną, która rzeczywiście przenosi fokus.MoveFocus is the related method that actually does move focus.

Dotyczy

Zobacz też