FrameworkElement.PredictFocus Method (FocusNavigationDirection)


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.

Namespace:   System.Windows
Assembly:  PresentationFramework (in PresentationFramework.dll)

Public Overrides NotOverridable Function PredictFocus (
	direction As FocusNavigationDirection
) As DependencyObject


Type: System.Windows.Input.FocusNavigationDirection

The direction for which a prospective focus change should be determined.

Return Value

Type: System.Windows.DependencyObject

The next element that focus would move to if focus were actually traversed. May return null if focus cannot be moved relative to this element for the provided direction.

Exception Condition

Specified one of the following directions in the TraversalRequest: Next, Previous, First, Last. These directions are not legal for PredictFocus (but they are legal for MoveFocus).

MoveFocus is the related method that actually does move focus.

The following example implements a handler that handles several possible button inputs, each button representing a possible FocusNavigationDirection. 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. 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 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

.NET Framework
Available since 3.0
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