WPF画布实现旋转等待效果

<Window x:Class="ScrolView.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        Title="MainWindow" Height="350" Width="525">
    <Grid>
        <Grid ShowGridLines="False" Grid.Row="3">
            <Grid.RowDefinitions>
                <RowDefinition Height="*"/>
                <RowDefinition Height="60"/>
            </Grid.RowDefinitions>

            <ContentControl x:Name="MainContent" Grid.RowSpan="2" Focusable="False" IsTabStop="False"/>
            <Label x:Name="Label_Hidden" Grid.RowSpan="2" Visibility="Hidden" Background="Transparent"/>
            <Popup x:Name="Progress" Grid.Row="0" Grid.RowSpan="2" Focusable="False" IsOpen="False"
                   AllowsTransparency="True" PopupAnimation="Fade" Placement="Center">
                <Canvas RenderTransformOrigin="0.5,0.5" HorizontalAlignment="Center" VerticalAlignment="Center" Width="120" Height="120" >
                    <Ellipse Width="21.835" Height="21.862" Canvas.Left="20.1696" Canvas.Top="9.76358" Stretch="Fill" Fill="Green" Opacity="0.9"/>
                    <Ellipse Width="21.835" Height="21.862" Canvas.Left="2.86816" Canvas.Top="29.9581" Stretch="Fill" Fill="Green" Opacity="0.8"/>
                    <Ellipse Width="21.835" Height="21.862" Canvas.Left="5.03758e-006" Canvas.Top="57.9341" Stretch="Fill" Fill="Green" Opacity="0.7"/>
                    <Ellipse Width="21.835" Height="21.862" Canvas.Left="12.1203" Canvas.Top="83.3163" Stretch="Fill" Fill="Green" Opacity="0.6"/>
                    <Ellipse Width="21.835" Height="21.862" Canvas.Left="36.5459" Canvas.Top="98.138" Stretch="Fill" Fill="Green" Opacity="0.5"/>
                    <Ellipse Width="21.835" Height="21.862" Canvas.Left="64.6723" Canvas.Top="96.8411" Stretch="Fill" Fill="Green" Opacity="0.4"/>
                    <Ellipse Width="21.835" Height="21.862" Canvas.Left="87.6176" Canvas.Top="81.2783" Stretch="Fill" Fill="Green" Opacity="0.3"/>
                    <Ellipse Width="21.835" Height="21.862" Canvas.Left="98.165" Canvas.Top="54.414" Stretch="Fill" Fill="Green" Opacity="0.2"/>
                    <Ellipse Width="21.835" Height="21.862" Canvas.Left="92.9838" Canvas.Top="26.9938" Stretch="Fill" Fill="Green" Opacity="0.1"/>
                    <Ellipse Width="21.835" Height="21.862" Canvas.Left="47.2783" Canvas.Top="0.5" Stretch="Fill" Fill="Green" Opacity="1.0"/>
                    <Canvas.RenderTransform>
                        <RotateTransform x:Name="SpinnerRotate" Angle="0" />
                    </Canvas.RenderTransform>
                    <Canvas.Triggers>
                        <EventTrigger RoutedEvent="ContentControl.Loaded">
                            <BeginStoryboard>
                                <Storyboard>
                                    <DoubleAnimation Storyboard.TargetName="SpinnerRotate" Storyboard.TargetProperty="(RotateTransform.Angle)" From="0" To="360" Duration="0:0:1" RepeatBehavior="Forever" />
                                </Storyboard>
                            </BeginStoryboard>
                        </EventTrigger>
                    </Canvas.Triggers>
                </Canvas>
            </Popup>
        </Grid>
    </Grid>
</Window>