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the following is the code for interface invaigationservice : using System.Windows.Controls;

namespace Airline_Reservation_System.Services
{
    public interface INavigationService
    {
        void NavigateTo<T>(object viewModel = null) where T : UserControl;
        void NavigateBack();
    }
}navigation service class : using System;
using System.Collections.Generic;
using System.Windows.Controls;

namespace Airline_Reservation_System.Services
{
    public class NavigationService : INavigationService
    {
        private readonly Func<Type, UserControl> _viewFactory;
        private readonly Action<UserControl> _setMainContent;
        private readonly Stack<UserControl> _navigationStack = new Stack<UserControl>();

        public NavigationService(Func<Type, UserControl> viewFactory, Action<UserControl> setMainContent)
        {
            _viewFactory = viewFactory;
            _setMainContent = setMainContent;
        }

        public void NavigateTo<T>(object viewModel = null) where T : UserControl
        {
            var view = _viewFactory(typeof(T));
            if (viewModel != null)
            {
                view.DataContext = viewModel;
            }
            if (_navigationStack.Count > 0)
            {
                _navigationStack.Push(view);
            }
            _setMainContent(view);
        }

        public void NavigateBack()
        {
            if (_navigationStack.Count > 1)
            {
                _navigationStack.Pop();
                var previousView = _navigationStack.Peek();
                _setMainContent(previousView);
            }
        }
    }
}