How to: Change the Speed of a Clock Without Changing the Speed of Its Timeline


A ClockController object's SpeedRatio property enables you to change the speed of a Clock without altering the SpeedRatio of the clock's Timeline. In the following example, a ClockController is used to interactively modify the SpeedRatio of a clock. The CurrentGlobalSpeedInvalidated event and the clock's CurrentGlobalSpeed property are used to display the clock's current global speed each time its interactive SpeedRatio is changed.

'  This example shows how to interactively control 
'  the speed of a clock

Imports System
Imports System.Windows
Imports System.Windows.Controls
Imports System.Windows.Media
Imports System.Windows.Shapes
Imports System.Windows.Media.Animation

Namespace Microsoft.Samples.Animation.TimingBehaviors
	Public Class ClockControllerSpeedRatioExample
		Inherits Page

		Private myControllableClock As AnimationClock
		Private speedRatioButton As Button
		Private speedRatioSettingTextBox As TextBox
		Private doubleParseResult As Double = 1
		Private currentGlobalSpeedTextBlock As TextBlock

		Public Sub New()
			Dim mainPanel As New StackPanel()

			' Create a rectangle to animate.
			Dim animatedRectangle As New Rectangle()
			animatedRectangle.Width = 100
			animatedRectangle.Height = 100
			animatedRectangle.Fill = Brushes.Orange
			' Create a DoubleAnimation to
			' animate its width.
			Dim widthAnimation As New DoubleAnimation(100, 500, New Duration(TimeSpan.FromSeconds(5)))
			'widthAnimation.RepeatBehavior = RepeatBehavior.Forever
			widthAnimation.AutoReverse = True
			widthAnimation.SpeedRatio = 0.5

			' Create a clock from the animation.
			myControllableClock = widthAnimation.CreateClock()

			' Apply the clock to the rectangle's Width property.
			animatedRectangle.ApplyAnimationClock(Rectangle.WidthProperty, myControllableClock)

			' Create some controls the enable the user to
			' interactively control the SpeedRatio of the clock. 
			Dim speedRatioDetailsPanel As New StackPanel()
			speedRatioDetailsPanel.Margin = New Thickness(0,20,0,20)
			speedRatioDetailsPanel.Orientation = Orientation.Horizontal
			Dim speedRatioLabel As New Label()
			speedRatioLabel.Content = "Speed Ratio:"

			' Create a text box so that the user can
			' specify the amount by which to seek.
			speedRatioSettingTextBox = New TextBox()
			speedRatioSettingTextBox.Text = myControllableClock.Controller.SpeedRatio.ToString()
			speedRatioSettingTextBox.VerticalAlignment = VerticalAlignment.Top
			AddHandler speedRatioSettingTextBox.TextChanged, AddressOf seekAmountTextBox_TextChanged

			' Create a button to apply SpeedRatio changes.
			speedRatioButton = New Button()
			speedRatioButton.Content = "Apply Speed Ratio"
			AddHandler speedRatioButton.Click, AddressOf speedRatioButton_Clicked


			' Display the clock's global speed information.
			Dim myLabel As New Label()
			myLabel.Content = "CurrentGlobalSpeed "
			currentGlobalSpeedTextBlock = New TextBlock()
			currentGlobalSpeedTextBlock.Text = myControllableClock.CurrentGlobalSpeed.ToString()

			' List for speed changes.
			AddHandler myControllableClock.CurrentGlobalSpeedInvalidated, AddressOf myControllableClock_currentGlobalSpeedInvalidated

			Me.Content = mainPanel
		End Sub

		' Updates the clock's SpeedRatio.
		Private Sub speedRatioButton_Clicked(ByVal sender As Object, ByVal e As RoutedEventArgs)

			' This statement triggers a CurrentGlobalSpeedInvalidated
			' event.
			myControllableClock.Controller.SpeedRatio = doubleParseResult

		End Sub

		' Displays the current global speed.
		Private Sub myControllableClock_currentGlobalSpeedInvalidated(ByVal sender As Object, ByVal e As EventArgs)

			currentGlobalSpeedTextBlock.Text = myControllableClock.CurrentGlobalSpeed.ToString() & " Event triggered at: " & Date.Now.ToString()

		End Sub

		' Verifies that speedRatioSettingTextBox has valid text content.
		' If it doesn't, the speedRatioButton is disabled.
		Private Sub seekAmountTextBox_TextChanged(ByVal sender As Object, ByVal e As TextChangedEventArgs)

			Dim theTextBox As TextBox = CType(e.Source, TextBox)
			If theTextBox.Text Is Nothing OrElse theTextBox.Text.Length < 1 OrElse Double.TryParse(theTextBox.Text, System.Globalization.NumberStyles.Any, Nothing, doubleParseResult) = False Then
				speedRatioButton.IsEnabled = False
				speedRatioButton.IsEnabled = True
			End If

		End Sub

	End Class
End Namespace