如何使用MediaElement关闭视频?

我有一个MediaElement，点击一个按钮，我打开了一个视频

<Button x:Name="VideoTour" Click="VideoTour_Click"  Grid.Column="4" Grid.ColumnSpan="2" Grid.Row="0" BorderBrush="{x:Null}" Style="{StaticResource ButtonStyle1}" VerticalAlignment="Top" Margin="0,14,0,0" Foreground="#FF5ACB2F" Background="{x:Null}">
        <Button.Content>
                <Image Source="../Assets/Movie.png" Width="40" Height="40"/>
        </Button.Content>
</Button> 
 <MediaElement x:Name="PlayTour" Visibility="Collapsed" Grid.Row="1" Grid.RowSpan="2" Grid.Column="1" Grid.ColumnSpan="4"  Source="{Binding URLtour}" AreTransportControlsEnabled="True" Width="260" Height="250"/>

当视频已经打开，我想提交一个按钮来关闭MediaElement视频，并设置Visibility属性collpsed，我该怎么办?

        PlayTour.Stop();