MVVM, UWP and MenuFlyout binding

control.xaml

<!-- helper is the namespace with your converter -->
<helper:MenuItemToMenuFlyoutConverter x:Key="menuToFlyout"/>
<!-- button is simply binded to a MenuItem instance -->
<Button x:Name="menuItem" FlyoutBase.AttachedFlyout="{Binding Converter={StaticResource menuToFlyout}}"
        Click="menuItem_Click" Content="{Binding Title}"/>

control.xaml.cs

// code behind
private void menuItem_Click(object sender, RoutedEventArgs e)
{
    var btn = sender as Button;
    var item = btn.DataContext as MenuItem;
    if(item.HasChildren)
    {
        FlyoutBase.ShowAttachedFlyout(btn);
    }
    else
    {
        item.Command.Execute(null);
    }
}

MenuItem.cs

// Using MVVM light, replace ViewModelBase with your MVVM framework
public class MenuItem : ViewModelBase
{
    private readonly List<MenuItem> _items = new List<MenuItem>();

    private readonly string _title;
    private RelayCommand _command;

    public MenuItem(string title)
        : this(title, new RelayCommand(()=> { }, () => { return false; }))
    { }

    public MenuItem(string title, RelayCommand command)
    {
        _title = title;
        _icon = icon;
        _command = command;
    }

    private MenuItem()
    {
        IsSeparator = true;
    }

    public bool IsSeparator { get; private set; }

    public List<MenuItem> Items
    {
        get
        {
            return _items;
        }
    }

    public bool HasChildren { get { return _items.Count > 0; } }

    public string Title { get { return _title; } }
    public RelayCommand Command { get { return _command; } }
}

MenuItemToMenuFlyoutConverter.cs

public class MenuItemToMenuFlyoutConverter : IValueConverter
{
    // this does not include sublevel menus right now
    public object Convert(object value, Type targetType, object parameter, string language)
    {
        var item = value as MenuItem;
        MenuFlyout menuFlyout = null;
        if (item.HasChildren)
        {
            menuFlyout = new MenuFlyout();
            menuFlyout.Opening += (object sender, object e) =>
                {
                    // if needed, check if your commands are available
                    MenuFlyout flyout = sender as MenuFlyout;
                    foreach (MenuFlyoutItem it in flyout.Items.Where(i => i is MenuFlyoutItem))
                    {
                        (it.Command as RelayCommand).RaiseCanExecuteChanged();
                    }
                };
            foreach (var subItem in item.Items)
            {
                MenuFlyoutItemBase flyoutItem;
                if (subItem.IsSeparator)
                {
                    flyoutItem = new MenuFlyoutSeparator();
                }
                else
                {
                    // if you have sublevel menus, you could call the converter for recursive menu creation here
                    menuFlyout.Placement = FlyoutPlacementMode.Bottom;
                    var menuFlyoutItem = new MenuFlyoutItem
                    {
                        Text = subItem.Title,
                        Command = subItem.Command
                    };
                    flyoutItem = menuFlyoutItem;
                }
                menuFlyout.Items.Add(flyoutItem);
            }
        }

        return menuFlyout;
    }

    public object ConvertBack(object value, Type targetType, object parameter, string language)
    {
        throw new NotImplementedException(); // we don't really care about going back
    }
}