FrameworkElement.PredictFocus(FocusNavigationDirection) 方法

定義

命名空間:

System.Windows

組件:

PresentationFramework.dll

決定下一個項目，該項目會針對所提供的焦點移動方向，接收相對於此項目的焦點，但是不會實際移動焦點。

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

參數

direction

FocusNavigationDirection

應用於決定預期焦點變更的方向。

傳回

DependencyObject

如果焦點實際上有周遊時，焦點會移動到的下一個項目。 如果無法依所提供的方向相對於此項目移動焦點，則可能傳回 null。

例外狀況

InvalidEnumArgumentException

在 TraversalRequest 中指定下列其中一個方向：Next、Previous、First、Last。 這些方向對 PredictFocus(FocusNavigationDirection) 而言不是合法的 (但對 MoveFocus(TraversalRequest) 而言是合法的)。

範例

下列範例會實作處理數個可能按鈕輸入的處理常式，每個按鈕代表可能的 FocusNavigationDirection 。 處理常式會追蹤具有目前鍵盤焦點的專案，並在該元素上呼叫 PredictFocus ，並指定適當 FocusNavigationDirection 做為所提供之類型參數的初始化 TraversalRequest 。 處理常式會變更預測焦點目的地的實體維度，而不是如往常一樣 MoveFocus 移至該元素。

    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

備註

MoveFocus 是實際移動焦點的相關方法。

另請參閱

• MoveFocus(TraversalRequest)
• PredictFocus(FocusNavigationDirection)