通过x:Class给ResourceDictionary内添加事件处理

我想给存在于CustomControl的Template里的事件添加处理程序(Storyboard.Completed发生的时候我想弹出一个对话框)，但却发生了异常，请大家帮忙看下哪里错了，我的代码如下：
xaml代码：<ResourceDictionary
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:local="clr-namespace:xClassTest"
    x:Class="xClassTest.Class1"
>
    <Style TargetType="{x:Type local:CustomControl1}">
        <Setter Property="Template">
            <Setter.Value>
                <ControlTemplate TargetType="{x:Type local:CustomControl1}">
                    <Viewbox>
                        <Grid x:Name="TheGrid" Width="50" Height="50">
                            <Rectangle x:Name="TheRect" Fill="LightBlue"/>
                        </Grid>
                    </Viewbox>
                    <ControlTemplate.Triggers>
                        <EventTrigger RoutedEvent="Grid.MouseEnter" SourceName="TheGrid">
                            <BeginStoryboard>
                                <Storyboard Completed="Storyboard_Completed">
                                    <DoubleAnimation To="100" Storyboard.TargetName="TheGrid"
                                                     Storyboard.TargetProperty="Width"/>
                                </Storyboard>
                            </BeginStoryboard>
                        </EventTrigger>
                        <EventTrigger RoutedEvent="Grid.MouseLeave" SourceName="TheGrid">
                            <BeginStoryboard>
                                <Storyboard Completed="Storyboard_Completed">
                                    <DoubleAnimation To="50" Storyboard.TargetName="TheGrid"
                                                     Storyboard.TargetProperty="Width"/>
                                </Storyboard>
                            </BeginStoryboard>
                        </EventTrigger>
                    </ControlTemplate.Triggers>
                </ControlTemplate>
            </Setter.Value>
        </Setter>
    </Style>
</ResourceDictionary>.cs codes:using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Imaging;
using System.Windows.Navigation;
using System.Windows.Shapes;namespace xClassTest
{
    public class CustomControl1 : Control
    {
        static CustomControl1()
        {
            DefaultStyleKeyProperty.OverrideMetadata(typeof(CustomControl1), new FrameworkPropertyMetadata(typeof(CustomControl1)));
        }
    }    public partial class Class1 : ResourceDictionary
    {
        public Class1()
        {
            InitializeComponent();
        }
        void Storyboard_Completed(object sender, EventArgs e)
        {
            MessageBox.Show("Completed!");
        }
    }
}
调用CustomControl1的代码:<Window x:Class="xClassTest.Window1"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:local="clr-namespace:xClassTest"
    Title="Window1" Height="300" Width="300">
    <Canvas>
        <local:CustomControl1/>
    </Canvas>
</Window>
以上代码Build没提示错误，但是Run的时候在Window1构造函数的InitializeComponent()方法处提示："无法重新初始化 ResourceDictionary 实例。  对象“xClassTest.Class1”行 4 位置 5 处的错误。"后来我发现，只要在CustomControl1的模板xaml文件那里的根元素添加：    x:Class="xClassTest.Class1"
这一行就有这个错误提示，请问是什么问题呢？如果要实现我开始描述的要求（Storyboard Completed事件发生的时候在C#代码部分做处理）应该怎么做呢？非常感谢您的帮助。