Artikel
11/18/2011

BackEase Class

Microsoft Silverlight will reach end of support after October 2021. Learn more.

Represents an easing function that retracts the motion of an animation slightly before it begins to animate in the path indicated.

Inheritance Hierarchy

System.Object
  System.Windows.DependencyObject
    System.Windows.Media.Animation.EasingFunctionBase
      System.Windows.Media.Animation.BackEase

Namespace: System.Windows.Media.Animation
Assembly: System.Windows (in System.Windows.dll)

Syntax

'Declaration
Public Class BackEase _
    Inherits EasingFunctionBase

public class BackEase : EasingFunctionBase

<BackEase .../>

The BackEase type exposes the following members.

Constructors

	Name	Description
	BackEase	Initializes a new instance of the BackEase class.

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Properties

	Name	Description
	Amplitude	Gets or sets the amplitude of retraction associated with a BackEase animation.
	Dispatcher	Gets the Dispatcher this object is associated with. (Inherited from DependencyObject.)
	EasingMode	Gets or sets a value that specifies how the animation interpolates. (Inherited from EasingFunctionBase.)

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Methods

	Name	Description
	CheckAccess	Determines whether the calling thread has access to this object. (Inherited from DependencyObject.)
	ClearValue	Clears the local value of a dependency property. (Inherited from DependencyObject.)
	Ease	Transforms normalized time to control the pace of an animation. (Inherited from EasingFunctionBase.)
	EaseInCore	Provides the logic portion of the easing function that you can override to produce the EaseIn mode of the custom easing function. (Overrides EasingFunctionBase.EaseInCore(Double).)
	Equals(Object)	Determines whether the specified Object is equal to the current Object. (Inherited from Object.)
	Finalize	Allows an object to try to free resources and perform other cleanup operations before the Object is reclaimed by garbage collection. (Inherited from Object.)
	GetAnimationBaseValue	Returns any base value established for a Silverlight dependency property, which would apply in cases where an animation is not active. (Inherited from DependencyObject.)
	GetHashCode	Serves as a hash function for a particular type. (Inherited from Object.)
	GetType	Gets the Type of the current instance. (Inherited from Object.)
	GetValue	Returns the current effective value of a dependency property from a DependencyObject. (Inherited from DependencyObject.)
	MemberwiseClone	Creates a shallow copy of the current Object. (Inherited from Object.)
	ReadLocalValue	Returns the local value of a dependency property, if a local value is set. (Inherited from DependencyObject.)
	SetValue	Sets the local value of a dependency property on a DependencyObject. (Inherited from DependencyObject.)
	ToString	Returns a string that represents the current object. (Inherited from Object.)

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Fields

	Name	Description
	AmplitudeProperty	Identifies the Amplitude dependency property.

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Remarks

You can control when the "back up" behavior occurs in an animation by specifying the EasingMode property value on an animation. The following graph demonstrate the different values of EasingMode, where f(t) represents the animation progress and t represents time.

BackEase EasingMode graphs.

The formula used for this function is the following.

BackEase formula.

Note:
Because this animation causes values to retract before progressing, the animation might interpolate into negative numbers unexpectedly. This can cause errors when animating properties that do not allow negative numbers. For example, if you apply this animation to the Height of an object (e.g. from 0 to 200 with an EasingMode of EaseIn), the animation will attempt to interpolate through negative numbers for Height which will throw an error.

Because this animation causes values to retract before progressing, the animation might interpolate into negative numbers unexpectedly. This can cause errors when animating properties that do not allow negative numbers. For example, if you apply this animation to the Height of an object (e.g. from 0 to 200 with an EasingMode of EaseIn), the animation will attempt to interpolate through negative numbers for Height which will throw an error.

There are several other easing functions besides BackEase, which you can explore using the following sample.

Run this sample

In addition to using the easing functions included in the run-time, you can create your own custom easing functions by inheriting from EasingFunctionBase.

Examples

The following example applies a BackEase easing function to a DoubleAnimation to create an animation that retracts slightly at the beginning and end of the animation.

Run this sample

<StackPanel x:Name="LayoutRoot" Background="White">
    <StackPanel.Resources>
        <Storyboard x:Name="myStoryboard">
            <DoubleAnimation From="1" To="2" Duration="00:00:1" 
                Storyboard.TargetName="myScaleTransform" 
                Storyboard.TargetProperty="ScaleX">
                <DoubleAnimation.EasingFunction>
                    <BackEase Amplitude="0.3" EasingMode="EaseInOut" />
                </DoubleAnimation.EasingFunction>
            </DoubleAnimation>
            <DoubleAnimation From="1" To="2" Duration="00:00:1" 
                Storyboard.TargetName="myScaleTransform" 
                Storyboard.TargetProperty="ScaleY">
                <DoubleAnimation.EasingFunction>
                    <BackEase Amplitude="0.3" EasingMode="EaseInOut" />
                </DoubleAnimation.EasingFunction>
            </DoubleAnimation>
        </Storyboard>
    </StackPanel.Resources>

    <Rectangle Margin="60" x:Name="myRectangle" MouseLeftButtonDown="Mouse_Clicked" 
     Fill="Blue" Width="50" Height="50" >

        <Rectangle.RenderTransform>
            <ScaleTransform x:Name="myScaleTransform" />
        </Rectangle.RenderTransform>

    </Rectangle>
</StackPanel>

' When the user clicks the rectangle, the animation
' begins. 
Private Sub Mouse_Clicked(ByVal sender As Object, ByVal e As MouseEventArgs)
    myStoryboard.Begin()
End Sub

// When the user clicks the rectangle, the animation
// begins. 
private void Mouse_Clicked(object sender, MouseEventArgs e)
{
    myStoryboard.Begin();
}

Version Information

Silverlight

Supported in: 5, 4, 3

Silverlight for Windows Phone

Supported in: Windows Phone OS 7.1, Windows Phone OS 7.0

Platforms

For a list of the operating systems and browsers that are supported by Silverlight, see Supported Operating Systems and Browsers.

Thread Safety

Any public static (Shared in Visual Basic) members of this type are thread safe. Any instance members are not guaranteed to be thread safe.

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