FrameworkElement.PredictFocus(FocusNavigationDirection) 方法

定义

命名空间:

System.Windows

程序集:

PresentationFramework.dll

根据提供的焦点移动方向，确定在此元素之后接收焦点的下一个元素，但不实际移动焦点。

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

参数

direction

FocusNavigationDirection

应确定其预期焦点更改的方向。

返回

DependencyObject

如果实际遍历了焦点，则为焦点将要移到的下一个元素。 如果焦点不能按提供的方向相对于此元素移动，则可能返回 null。

例外

InvalidEnumArgumentException

在 TraversalRequest 中指定了以下方向之一：Next、Previous、First、Last。 对于 PredictFocus(FocusNavigationDirection) 来说，这些方向是非法的（但对于 MoveFocus(TraversalRequest) 来说是合法的）。

示例

以下示例实现一个处理程序，该处理程序处理多个可能的按钮输入，每个按钮表示一个可能的 FocusNavigationDirection。 处理程序使用当前键盘焦点跟踪元素，并调用 PredictFocus 该元素，并为所提供的类型参数指定适当的 FocusNavigationDirection 初始化 TraversalRequest 。 处理程序不会像往 MoveFocus 那样移动到该元素，而是为了可视化目的更改预测焦点目标的物理维度。

    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

注解

MoveFocus 是实际移动焦点的相关方法。

另请参阅

• MoveFocus(TraversalRequest)
• PredictFocus(FocusNavigationDirection)