presence_sample_v2/Presence.Desktop/ViewModels/MainWindowViewModel.cs

using domain.UseCase;
using DynamicData;
using DynamicData.Binding;
using Presence.Desktop.Models;
using ReactiveUI;
using System;
using System.Collections.Generic;
using System.Collections.ObjectModel;
using System.Linq;
using System.Reactive.Linq;
using Tmds.DBus.Protocol;

namespace Presence.Desktop.ViewModels
{
    public class MainWindowViewModel : ViewModelBase
    {
        private readonly IGroupUseCase _groupService;
        private List<GroupPresenter> groupPresentersDataSource = new List<GroupPresenter>();
        private ObservableCollection<GroupPresenter> _groups;
        public ObservableCollection<GroupPresenter> Groups => _groups;

        public GroupPresenter? SelectedGroupItem { 
            get => _selectedGroupItem; 
            set => this.RaiseAndSetIfChanged(ref _selectedGroupItem, value); }

        private GroupPresenter? _selectedGroupItem;



        public ObservableCollection<UserPresenter> Users { get => _users;}
        public ObservableCollection<UserPresenter> _users;
        public MainWindowViewModel(IGroupUseCase groupUseCase)
        {
            _groupService = groupUseCase;

            foreach (var item in _groupService.GetGroupsWithStudents())
            {
                GroupPresenter groupPresenter = new GroupPresenter
                {
                    Id = item.Id,
                    Name = item.Name,
                    users = item.Users?.Select(user => new UserPresenter
                    {
                        Name = user.Name,
                        Guid = user.Guid,
                        Group = new GroupPresenter { Id = item.Id, Name = item.Name }
                    }
                    ).ToList()
                };
                groupPresentersDataSource.Add(groupPresenter);
            }
            _groups = new ObservableCollection<GroupPresenter>(groupPresentersDataSource);
            
            _users = new ObservableCollection<UserPresenter>();

            this.WhenAnyValue(vm => vm.SelectedGroupItem)
                .Subscribe(_ => SetUsers());

        }

        private void SetUsers()
        {
            if(SelectedGroupItem == null) return;
            if (SelectedGroupItem.users == null) return;
            Users.Clear();
            foreach (var item in SelectedGroupItem.users)
            {
                Users.Add(item);
            }
        }
    }
}