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我正在學習WPF動畫，並用一個非常簡單的動畫創建了一個簡單的演示應用程序。我已將主柵格分爲三行;頂部的按鈕行，以及屏幕剩餘部分的兩個內容行，一個紅色和一個藍色。完整的XAML如下。爲什麼不能使用此動畫？
有兩個按鈕，顯示紅色和顯示藍色。當每個按鈕被按下時，我希望按鈕行下方的區域通過緩慢的從上到下的擦拭來改變顏色。故事板設置兩行，以0的高度，然後動畫所需的行到1×的高度，這樣的：
<Storyboard>
<Utility:GridLengthAnimation Storyboard.TargetName="RedRow" Storyboard.TargetProperty="Height" To="0" Duration="0:0:0" />
<Utility:GridLengthAnimation Storyboard.TargetName="BlueRow" Storyboard.TargetProperty="Height" To="0" Duration="0:0:0" />
<Utility:GridLengthAnimation Storyboard.TargetName="BlueRow" Storyboard.TargetProperty="Height" From="0" To="1*" Duration="0:0:5" />
</Storyboard>
的顏色改變爲預期的，但沒有動畫。所以，我的問題很簡單：爲什麼不動畫工作？
我正在使用自定義動畫類GridLengthAnimation（改編自this CodeProject article）爲網格長度設置動畫。我已經複製了下面的課程。
要重新創建演示項目：要重新創建我的演示項目，創建一個新的WPF項目（我用VS 2010）並用以下替換XAML中MainWindow.xaml：
<Window x:Class="WpfApplication1.MainWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" xmlns:Utility="clr-namespace:Utility" Title="MainWindow" Height="350" Width="525">
<Grid>
<Grid.RowDefinitions>
<RowDefinition Name="Buttons" Height="35" />
<RowDefinition Name="RedRow" Height="0.5*" />
<RowDefinition Name="BlueRow" Height="0.5*" />
</Grid.RowDefinitions>
<!-- Buttons -->
<StackPanel Orientation="Horizontal" HorizontalAlignment="Center">
<Button Content="Show Red" Width="100" Margin="5" >
<Button.Triggers>
<EventTrigger RoutedEvent="Button.Click">
<EventTrigger.Actions>
<BeginStoryboard>
<Storyboard>
<Utility:GridLengthAnimation Storyboard.TargetName="RedRow" Storyboard.TargetProperty="Height" To="0" Duration="0:0:0" />
<Utility:GridLengthAnimation Storyboard.TargetName="BlueRow" Storyboard.TargetProperty="Height" To="0" Duration="0:0:0" />
<Utility:GridLengthAnimation Storyboard.TargetName="RedRow" Storyboard.TargetProperty="Height" From="0" To="1*" Duration="0:0:5" />
</Storyboard>
</BeginStoryboard>
</EventTrigger.Actions>
</EventTrigger>
</Button.Triggers>
</Button>
<Button Content="Show Blue" Width="100" Margin="5" >
<Button.Triggers>
<EventTrigger RoutedEvent="Button.Click">
<EventTrigger.Actions>
<BeginStoryboard>
<Storyboard>
<Utility:GridLengthAnimation Storyboard.TargetName="RedRow" Storyboard.TargetProperty="Height" To="0" Duration="0:0:0" />
<Utility:GridLengthAnimation Storyboard.TargetName="BlueRow" Storyboard.TargetProperty="Height" To="0" Duration="0:0:0" />
<Utility:GridLengthAnimation Storyboard.TargetName="BlueRow" Storyboard.TargetProperty="Height" From="0" To="1*" Duration="0:0:5" />
</Storyboard>
</BeginStoryboard>
</EventTrigger.Actions>
</EventTrigger>
</Button.Triggers>
</Button>
</StackPanel>
<!-- Grid Fills-->
<Border Grid.Row="1" Background="Red" />
<Border Grid.Row="2" Background="Blue" />
</Grid>
</Window>
沒有代碼 - 後面加入了MainWindow.xaml。
將C＃類添加到名爲GridLengthAnimation.cs的項目中。用以下代碼替換該類中的代碼：
using System;
using System.Windows.Media.Animation;
using System.Windows;
namespace Utility
{
/// <summary>
/// Enables animation of WPF Grid row heights and column widths.
/// </summary>
/// <remarks>Adapted from Graus & Sivakumar, "WPF Tutorial - Part 2 : Writing a custom animation class",
/// http://www.codeproject.com/KB/WPF/GridLengthAnimation.aspx, retrieved 08/12/2010.</remarks>
internal class GridLengthAnimation : AnimationTimeline
{
static GridLengthAnimation()
{
FromProperty = DependencyProperty.Register("From", typeof(GridLength),
typeof(GridLengthAnimation));
ToProperty = DependencyProperty.Register("To", typeof(GridLength),
typeof(GridLengthAnimation));
}
public override Type TargetPropertyType
{
get
{
return typeof(GridLength);
}
}
protected override Freezable CreateInstanceCore()
{
return new GridLengthAnimation();
}
public static readonly DependencyProperty FromProperty;
public GridLength From
{
get
{
return (GridLength)GetValue(FromProperty);
}
set
{
SetValue(FromProperty, value);
}
}
public static readonly DependencyProperty ToProperty;
public GridLength To
{
get
{
return (GridLength)GetValue(ToProperty);
}
set
{
SetValue(ToProperty, value);
}
}
public override object GetCurrentValue(object defaultOriginValue, object defaultDestinationValue, AnimationClock animationClock)
{
double fromVal = ((GridLength)GetValue(FromProperty)).Value;
double toVal = ((GridLength)GetValue(ToProperty)).Value;
if (animationClock.CurrentProgress != null)
{
if (fromVal > toVal)
{
return new GridLength((1 - animationClock.CurrentProgress.Value) * (fromVal - toVal) + toVal, GridUnitType.Star);
}
else
{
return new GridLength(animationClock.CurrentProgress.Value * (toVal - fromVal) + fromVal, GridUnitType.Star);
}
}
else
{
return null;
}
}
}
}