work/Visor/Visor/Components/TodoApp/BaseTodoItems.cs

using Microsoft.AspNetCore.Components;

namespace Visor.Components.TodoApp
{
    public abstract class BaseTodoItems : ComponentBase
    {
        protected Validations? validations;

        protected string? description;

        protected Filter filter = Filter.All;

        protected List<Todo> todos = new()
            {
                new() { Description = "Buy milk" },
                new() { Description = "Call John regarding the meeting" },
                new() { Description = "Walk a dog" },
            };

        protected IEnumerable<Todo> Todos
        {
            get
            {
                var query = from t in todos select t;

                if (filter == Filter.Active)
                    query = from q in query where !q.Completed select q;

                if (filter == Filter.Completed)
                    query = from q in query where q.Completed select q;

                return query;
            }
        }

        protected void SetFilter(Filter filter)
        {
            this.filter = filter;
        }

        protected void OnCheckAll(bool isChecked)
        {
            todos.ForEach(x => x.Completed = isChecked);
        }

        protected async Task OnAddTodo()
        {
            if (await validations!.ValidateAll())
            {
                todos.Add(new() { Description = description });
                description = null;

                await validations.ClearAll();
            }
        }

        protected void OnClearCompleted()
        {
            todos.RemoveAll(x => x.Completed);
            filter = Filter.All;
        }

        protected Task OnTodoStatusChanged(bool isChecked)
        {
            return InvokeAsync(StateHasChanged);
        }
    }
}