how can i get the selected item header in HandyControl hc:SideMenu WPF

i am using handy controls and this is first time to use it so i am facing some difficulties

in test app i am using hc:SideMenu

and i can get out the selected item header from the hc:SideMenu

<hc:SideMenu
    x:Name="MySideMenu"
    Grid.Column="0"
    Width="200"
    Margin="5"
    BorderThickness="1"
    SelectionChanged="MySideMenu_SelectionChanged">

    <hc:Interaction.Triggers>
        <hc:EventTrigger EventName="SelectionChanged">
            <hc:EventToCommand Command="{Binding SwitchItemCmd}" PassEventArgsToCommand="True" />
        </hc:EventTrigger>
    </hc:Interaction.Triggers>

    <hc:SideMenuItem Header="Overview" IsSelected="True">

        <hc:SideMenuItem.Icon>
            <Image
                Width="24"
                Height="24"
                Source="/Folder/01.png" />
        </hc:SideMenuItem.Icon>

        <hc:SideMenuItem
            x:Name="MySummary"
            Command="{Binding SelectCmd}"
            CommandParameter="{Binding Header, RelativeSource={RelativeSource Self}}"
            Header="Summary"
            IsSelected="False">
            <hc:SideMenuItem.Icon>
                <TextBlock Text="&#xf2cb;" />
            </hc:SideMenuItem.Icon>
        </hc:SideMenuItem>

        <hc:SideMenuItem
            Command="{Binding SelectCmd}"
            CommandParameter="{Binding Header, RelativeSource={RelativeSource Self}}"
            Header="Dashboards">
            <hc:SideMenuItem.Icon>
                <TextBlock Text="&#xf246;" />
            </hc:SideMenuItem.Icon>
        </hc:SideMenuItem>

        <hc:SideMenuItem
            Command="{Binding SelectCmd}"
            CommandParameter="{Binding Header, RelativeSource={RelativeSource Self}}"
            Header="Wiki">
            <hc:SideMenuItem.Icon>
                <TextBlock Text="&#xe82d;" />
            </hc:SideMenuItem.Icon>
        </hc:SideMenuItem>
    </hc:SideMenuItem>

</hc:SideMenu>

and C# code is

private void MySideMenu_SelectionChanged(object sender, HandyControl.Data.FunctionEventArgs e) {

string SelectedItemHeader = ((HeaderedSimpleItemsControl)MySideMenu.Header).ToString();
textBox.Text = SelectedItemHeader;

}

Try this:

private void MySideMenu_SelectionChanged(object sender, 
    HandyControl.Data.FunctionEventArgs<object> e)
{
    SideMenuItem sideMenuItem = e.Info as SideMenuItem;
    textBox.Text = sideMenuItem?.Header?.ToString();
}