<ResourceDictionary
    x:Class="UnoAppIssues.Resources.ResourceDictionaryWithCodeBehind"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">

    <MenuFlyout x:Key="someFlyout">
        <MenuFlyoutItem Click="MenuFlyoutItem_Click" Text="Some text" />
    </MenuFlyout>

</ResourceDictionary>

public sealed partial class ResourceDictionaryWithCodeBehind : ResourceDictionary
    {
        public ResourceDictionaryWithCodeBehind()
        {
            this.InitializeComponent();
        }

        private void MenuFlyoutItem_Click(object sender, RoutedEventArgs e)
        {

        }
    }