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DiscreteDoubleKeyFrame

Silverlight

Animates from the Double value of the previous key frame to the Value of the current key frame, by using discrete values.

<DiscreteDoubleKeyFrame   .../>

A key frame defines a segment of the DoubleAnimationUsingKeyFrames object to which it belongs. Each key frame has a target Value and a KeyTime. The KeyTime specifies the time at which the key frame's Value should be reached. The animation progresses from the target value of the previous key frame to the target value of the current key frame. The animation starts when the previous key frame ends, and the animation ends when the key time of the current key frame is reached.

Discrete key frames, such as DiscreteDoubleKeyFrame, create sudden jumps between values (no interpolation). The animated property does not change until the key frame's key time is reached, at which point the animated property suddenly changes to the target value.

For more information on basic concepts, see Key-Frame Animations. Note that the Key-Frame Animations topic is written primarily for users of the managed API, and may not have code examples or specific information that address the JavaScript API scenarios.

The following example moves a rectangle across a screen. The example uses a DoubleAnimationUsingKeyFrames object to animate the X property of a TranslateTransform object applied to a Rectangle object. This animation, which repeats indefinitely, uses three key frames in the following manner:

  1. During the first three seconds, a LinearDoubleKeyFrame object moves the rectangle along a path at a steady rate from its starting position to the 500 position. Linear key frames, such as LinearDoubleKeyFrame, create a smooth linear transition between values.

  2. At the end of the fourth second, a DiscreteDoubleKeyFrame object suddenly moves the rectangle to the next position. Discrete key frames, such as DiscreteDoubleKeyFrame, create sudden jumps between values. In this example, the rectangle is at the starting position and then suddenly appears at the 500 position.

  3. In the final two seconds, a SplineDoubleKeyFrame object moves the rectangle back to its starting position. Spline key frames, such as SplineDoubleKeyFrame, create a variable transition between values according to the value of the KeySpline property. A KeySpline provides a nonlinear way to alter the relationship of time versus value during the animation duration. In particular, the relationship can be a curve that would be difficult to produce with individual key frames. In this example, the rectangle begins by moving slowly and then speeds up exponentially toward the end of the time segment.

<Canvas
  xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
  xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
  Width="400" Height="300">
  <Rectangle Fill="Blue" 
    Width="50" Height="50">
    <Rectangle.RenderTransform>
      <TranslateTransform 
        x:Name="MyAnimatedTranslateTransform" 
        X="0" Y="0" />
    </Rectangle.RenderTransform>
    <Rectangle.Triggers>
      <EventTrigger RoutedEvent="Rectangle.Loaded">
        <BeginStoryboard>
          <Storyboard>

            <!-- Animate the TranslateTransform X property
                 from 0 to 350, then 50,
                 then 200 over 10 seconds. -->
            <DoubleAnimationUsingKeyFrames
              Storyboard.TargetName="MyAnimatedTranslateTransform"
              Storyboard.TargetProperty="X"
              Duration="0:0:10">

                <!-- Using a LinearDoubleKeyFrame, the rectangle moves 
                     steadily from its starting position to 500 over 
                     the first 3 seconds.  -->
                <LinearDoubleKeyFrame Value="500" KeyTime="0:0:3" />

                <!-- Using a DiscreteDoubleKeyFrame, the rectangle suddenly 
                     appears at 400 after the fourth second of the animation. -->
                <DiscreteDoubleKeyFrame Value="400" KeyTime="0:0:4" />

                <!-- Using a SplineDoubleKeyFrame, the rectangle moves 
                     back to its starting point. The
                     animation starts out slowly at first and then speeds up. 
                     This KeyFrame ends after the sixth
                     second. -->
                <SplineDoubleKeyFrame KeySpline="0.6,0.0 0.9,0.00" Value="0" KeyTime="0:0:6" />
 
            </DoubleAnimationUsingKeyFrames>
          </Storyboard>
        </BeginStoryboard>
      </EventTrigger>
    </Rectangle.Triggers> 
  </Rectangle>
</Canvas>

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