实在搞不懂，自定义控件中动画有关问题，

<ResourceDictionary
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:vsm="clr-namespace:System.Windows;assembly=System.Windows"
    xmlns:local="clr-namespace:SLClient" >

    <!--The default style of MyCtrl-->
    <Style TargetType="local:MyCtrl">
        <!--设置默认样式-->
        <Setter Property="Width" Value="100"/>
        
        <!--在该样式中，设置其模板内容-->
        <Setter Property="Template">
            <Setter.Value>
                <!-- 定义模板 -->
                <ControlTemplate TargetType="local:MyCtrl">
                    <!--该模板中，应只有一个可视元素，在此用Grid-->
                    <Grid>
                        <!--定义可视状态组-->
                        <vsm:VisualStateManager.VisualStateGroups>
                            <!-- 数据有效性状态组 -->
                            <VisualStateGroup x:Name="ValidStates">
                                <VisualState x:Name="Valid" />
                                <VisualState x:Name="UnValid" />
                                <!--定义状态转换动作-->
                                <VisualStateGroup.Transitions>
                                    <!--当跳转至该状态时，进行转换-->
                                    <VisualTransition To="UnValid">
                                        <!--时间轴-->
                                        <Storyboard>
                                            <!--动画设定.颜色渐变-->
                                            <ColorAnimation Storyboard.TargetName="textBox"
                                                Storyboard.TargetProperty="(TextBox.Foreground).(SolidColorBrush.Color)"
                                                To="Red"/>
                                        </Storyboard>
                                    </VisualTransition>
                                    <VisualTransition To="Valid">
                                        <!--时间轴-->
                                        <Storyboard>
                                            <!--动画设定.颜色渐变-->
                                            <ColorAnimation Storyboard.TargetName="textBox"
                                                Storyboard.TargetProperty="(TextBox.Foreground).(SolidColorBrush.Color)"
                                                To="Blue"/>
                                        </Storyboard>
                                    </VisualTransition>
                                </VisualStateGroup.Transitions>
                            </VisualStateGroup>
                        </vsm:VisualStateManager.VisualStateGroups>
                        <!--文本框-->
                        <TextBox Name="textBox" Margin="0,0,0,0" Grid.Column="0" Grid.Row="0"></TextBox>
                    </Grid>
                </ControlTemplate>
            </Setter.Value>
        </Setter>
    </Style>
</ResourceDictionary>

using System;
using System.Collections.Generic;
using System.Linq;
using System.Net;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Animation;
using System.Windows.Shapes;

namespace SLClient
{
    //定义该类的部件和状态
    [TemplatePart(Name = "textBox", Type = typeof(TextBox))]
    [TemplateVisualState(Name = "Valid", GroupName = "ValidStates")]
    [TemplateVisualState(Name = "UnValid", GroupName = "ValidStates")]
    //我知道实现这样的功能，直接扩展TextBox更方便
    //之所以这样做，只是想练习一下怎么做一个自定义控件罢了
    //所以别告诉我应该扩展自TextBox，而不是 Control
    public class MyCtrl : Control
    {
        public MyCtrl()
        {
            //设置默认样式
            this.DefaultStyleKey = typeof(MyCtrl);
        }

        //重载父类方法，当对该控件应用模板时该方法执行
        public override void OnApplyTemplate()
        {
            base.OnApplyTemplate();
            //获取模板中的部件
            this.TextBox = this.GetTemplateChild("textBox") as TextBox;
        }

        private TextBox textBox;
        protected TextBox TextBox
        {
            get { return this.textBox; }
            set
            {
                if (this.textBox != null)
                {//取消事件注册
                    this.textBox.TextChanged -= new TextChangedEventHandler(textBox_TextChanged);
                    
                }
                this.textBox = value;
                if (this.textBox != null)
                {//部件事件注册
                    this.textBox.TextChanged += new TextChangedEventHandler(textBox_TextChanged);
                }
            }
        }

        void textBox_TextChanged(object sender, TextChangedEventArgs e)
        {
            //数据有效性的判断
            decimal num;
            bool valid = Decimal.TryParse(this.textBox.Text, out num);
            if (valid)
            {
                VisualStateManager.GoToState(this, "Valid", true);
            }
            else
            {
                VisualStateManager.GoToState(this, "UnValid", true);
            }
        }
    }
}