/// <summary>
/// Handles a change to the TickTime property.
/// </summary>
/// <param name="dependencyObject">The DependencyObject on which the property has changed value.</param>
/// <param name="dependencyPropertyChangedEventArgs">Event data that that tracks changes to the effective value of this property.</param>
static void OnTickTimePropertyChanged(DependencyObject dependencyObject, DependencyPropertyChangedEventArgs dependencyPropertyChangedEventArgs)
{
// IMPORTANT CONCEPT: in any virtualized panel, we need to accept that any given control can be recycled and re-realized at any time, even during an
// animation which could last several seconds. To account for this in our design, we don't store the state of any animation. When a new data context is
// provided for this control, we'll use the start time from the View Model and the current time and calculate how much time is left in the animation. In
// this way, when a PriceControl is realized, it will pick up how far into the animation cycle we are and provide animation only for as long as the
// control is realized (or until the animation is complete).
PriceControl priceControl = dependencyObject as PriceControl;
Duration elapsedTime = new Duration(DateTime.Now.Subtract((DateTime)dependencyPropertyChangedEventArgs.NewValue));
// This will animate the background in the currently selected background color until the time since the last tick is equal to or greater than the
// PriceControl.TickDuration property.
if (elapsedTime < priceControl.TickDuration)
{
// This is the amount of time remaining in the animation.
Duration remainingDuration = priceControl.TickDuration - elapsedTime;
// The most important part of this animation, to make it appear as if we've been keeping track of all the price changes in the entire virtual
// space, is to calculate the current age of the tick and from that interpolate the current state of animation.
Double proRata = remainingDuration.TimeSpan.TotalMilliseconds / priceControl.TickDuration.TimeSpan.TotalMilliseconds;
Double from = priceControl.TickOpacity * proRata;
// We will only animate this control as long as it is realized or until the interpolated animation has completed. Note that we take the time to
// clean up after the animation is completed as there are likely to be many items that are animated and the lifetime of any one PriceControl is
// indefinite. Note that this is a relatively slow animation and there will likely be many of them, so we've chosen a framerate that will not
// overly tax the CPU.
DoubleAnimation opacityAnimation = new DoubleAnimation();
opacityAnimation.Completed += priceControl.OnAnimationCompleted;
opacityAnimation.Duration = remainingDuration;
opacityAnimation.FillBehavior = FillBehavior.Stop;
opacityAnimation.From = from;
Timeline.SetDesiredFrameRate(opacityAnimation, 4);
priceControl.BeginAnimation(PriceControl.MaskOpacityProperty, opacityAnimation, HandoffBehavior.SnapshotAndReplace);
}
}
/// <summary>
/// Handles a change to the LastPrice property.
/// </summary>
/// <param name="dependencyObject">The DependencyObject on which the property has changed value.</param>
/// <param name="dependencyPropertyChangedEventArgs">Event data that that tracks changes to the effective value of this property.</param>
static void OnLastPricePropertyChanged(DependencyObject dependencyObject, DependencyPropertyChangedEventArgs dependencyPropertyChangedEventArgs)
{
// This makes sure that the mask background color reflect the direction of the price change.
PriceControl priceControl = dependencyObject as PriceControl;
priceControl.MaskBackground = priceControl.LastPrice <priceControl.Price?priceControl.TickUpBackground :
priceControl.LastPrice> priceControl.Price ? priceControl.TickDownBackground :
null;
}
/// <summary>
/// Handles a change to the Price property.
/// </summary>
/// <param name="dependencyObject">The DependencyObject on which the property has changed value.</param>
/// <param name="dependencyPropertyChangedEventArgs">Event data that that tracks changes to the effective value of this property.</param>
static void OnPricePropertyChanged(DependencyObject dependencyObject, DependencyPropertyChangedEventArgs dependencyPropertyChangedEventArgs)
{
// This will make sure that the background mask reflects the proper price change
PriceControl priceControl = dependencyObject as PriceControl;
priceControl.MaskBackground = priceControl.LastPrice <priceControl.Price?priceControl.TickUpBackground :
priceControl.LastPrice> priceControl.Price ? priceControl.TickDownBackground :
null;
priceControl.Content = priceControl.Price;
}