Xamarin Forms Flyout Page with Navigation Page

Question

In my new Xamarin.Forms App I start with Login Page witch is rendered as NavigationPage. After the login I show the user a Flyout Page. If an item from the Flyout is selected this page will be displayed in the Detail section of the Flyout Page as Navigation Page. The selected page has a button and when the user tapps the button I want to navigate to a new Navigation Page witch is not rendered in the Flyout Page.
I have tried to convert the FlyoutPage to a NavigationPage, but this wasn't a good idea.
Do you have any idea to solve this problem? When I navigate to the new NavigationPage the user should not be able to see or to open the Flyout.

Here you can see my XAML:

<FlyoutPage>

    <FlyoutPage.Flyout>
        <pages:RootPageFlyout x:Name="FlyoutPage" />
    </FlyoutPage.Flyout>

    <FlyoutPage.Detail>
        <NavigationPage>
            <x:Arguments>
                <pages:MainPage />
            </x:Arguments>
        </NavigationPage>
    </FlyoutPage.Detail>

</FlyoutPage>

And this is the code behind of the XAML

public partial class RootPage : FlyoutPage
{
    public RootPage()
    {
        InitializeComponent();
        FlyoutPage.ListView.ItemSelected += ListView_ItemSelected;
    }

    private void ListView_ItemSelected(object sender, SelectedItemChangedEventArgs e)
    {
        var item = e.SelectedItem as RootPageFlyoutMenuItem;
        if (item == null) return;

        var page = (Page)Activator.CreateInstance(item.TargetType);
        page.Title = item.Title;

        Detail = new NavigationPage(page);
        IsPresented = false;

        FlyoutPage.ListView.SelectedItem = null;
    }
}