如何在window 10 uwp中折叠ExpandPanel

<Grid>
    <controls:ExpandPanel x:Name="expandPanel" Header="ExpandPanel">
        <!-- 内容 -->
    </controls:ExpandPanel>
</Grid>

private void ToggleExpandPanel()
{
    expandPanel.IsExpanded = !expandPanel.IsExpanded;
}

<controls:ExpandPanel x:Name="expandPanel" Header="ExpandPanel">
    <VisualStateManager.VisualStateGroups>
        <VisualStateGroup>
            <VisualState x:Name="Expanded">
                <Storyboard>
                    <!-- 展开时的动画效果 -->
                </Storyboard>
            </VisualState>
            <VisualState x:Name="Collapsed">
                <Storyboard>
                    <!-- 折叠时的动画效果 -->
                </Storyboard>
            </VisualState>
        </VisualStateGroup>
    </VisualStateManager.VisualStateGroups>
    <!-- 内容 -->
</controls:ExpandPanel>