BackEase Class
[ This article is for Windows Phone 8 developers. If you’re developing for Windows 10, see the latest documentation. ]
Represents an easing function that retracts the motion of an animation slightly before it begins to animate in the path indicated.
System.Windows::DependencyObject
System.Windows.Media.Animation::EasingFunctionBase
System.Windows.Media.Animation::BackEase
Assembly: System.Windows (in System.Windows.dll)
XMLNS for XAML: Not mapped to an xmlns.
The BackEase type exposes the following members.
| 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.) |
| 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 Windows Phone 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.) |
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.
The formula used for this function is the following.
 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. |
In addition to using the easing functions included in the run-time, you can create your own custom easing functions by inheriting from EasingFunctionBase.
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.
<StackPanel x:Name="LayoutRoot" Background="Transparent"> <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 void Mouse_Clicked(object sender, MouseEventArgs e) { myStoryboard.Begin(); }