请教有关StoryBoard的问题

[weixin_38067167]

我在窗体中做了一个loading的图标：
<Path Name="LoadingIcon2" Stroke="#888" Visibility="Collapsed" StrokeThickness="3" Width="24" Height="24" RenderTransformOrigin="0.5,0.5" Panel.ZIndex="100" HorizontalAlignment="Left" VerticalAlignment="Bottom" Margin="6 0 0 6">
<Path.RenderTransform>
<RotateTransform Angle="0"></RotateTransform>
</Path.RenderTransform>
<Path.Data>
<GeometryGroup>
<PathGeometry Figures="M 12,2 A 10,10 0 1 0 22,12"></PathGeometry>
</GeometryGroup>
</Path.Data>
</Path>


然后通过代码去显示，并且让其旋转：
private void ShowLoading()
{
LoadingIcon2.Visibility = Visibility.Visible;
LoadingIcon2.Opacity = 1;
DoubleAnimation ani = new DoubleAnimation(0, 360, TimeSpan.FromMilliseconds(1000));
Storyboard st = new Storyboard();
Storyboard.SetTarget(ani, LoadingIcon2);
Storyboard.SetTargetProperty(ani, new PropertyPath("RenderTransform.Angle"));
st.RepeatBehavior = RepeatBehavior.Forever;
st.Children.Add(ani);
st.Begin();
}
private void CloseLoading()
{
DoubleAnimation ani = new DoubleAnimation(1, 0, TimeSpan.FromMilliseconds(500));
ani.EasingFunction = new CubicEase();
Storyboard st = new Storyboard();
Storyboard.SetTarget(ani, LoadingIcon2);
Storyboard.SetTargetProperty(ani, new PropertyPath("Opacity"));
st.Children.Add(ani);
st.Completed += (o, evt) =>
{
LoadingIcon2.Visibility = Visibility.Collapsed;
};
st.Begin();
}


showLoading方法可以让那个图标产生旋转效果；
然后调用CloseLoading方法，可以将图标淡出并最终隐藏起来；
当我按照：showLoading - CloseLoading的顺序去调用的时候，产生的效果正如我预想中的那样；
可是，当我Close了之后再Show的时候，却发现图标不显示了。我明明在Show方法那里强制将Opacity设置为1的，可是通过“实时可视化树”查看对象属性，却发现Opacity为零，这是为什么？


da jia hao!