实在搞不懂，自定义控件中动画问题，求助～！

<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);

            }

        }

    }

}