DynamicPolymorphicListController.cs

using System;
using System.Collections.Generic;
using Microsoft.AspNetCore.Mvc;
using PolymorphicModelBinder.Samples.Mvc.Models;
using PolymorphicModelBinder.Samples.Mvc.Models.Devices;
using PolymorphicModelBinder.Samples.Mvc.Models.Pets;

namespace PolymorphicModelBinder.Samples.Mvc.Controllers
{
    public class DynamicPolymorphicListController : Controller
    {
        [HttpGet]
        public IActionResult Index()
        {
            return View(new DynamicPolymorphicListViewModel()
            {
                Pets = new List<Pet>()
                {
                    new Cat()
                    {
                        Name = "Garfield",
                        CanMeow = true
                    },
                    new Dog()
                    {
                        Name = "Noeska",
                        CanBark = true,
                    }
                }
            });
        }
    
        [HttpPost]
        public IActionResult Index(DynamicPolymorphicListViewModel viewModel)
        {
            return View(viewModel);
        }
    
        [HttpPost]
        public IActionResult AddEntry(DynamicPolymorphicListViewModel viewModel, string type)
        {
            viewModel.Pets.Add(type switch
            {
                "Dog" => new Dog() { Name = "New dog" },
                "Cat" => new Cat() { Name = "New cat" },
                _ => throw new ArgumentOutOfRangeException(nameof(type))
            });
            return PartialView(viewModel);
        }
    }
}