FrameworkElement.PredictFocus(FocusNavigationDirection) 方法
定義
重要
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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.DependencyObjectPublic 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
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
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。
