blazor-lifetime/Shared/AdvancedComponentBase.cs

using System.Threading.Tasks;
using Microsoft.AspNetCore.Components;
using blazor_lifetime.Models;

namespace blazor_lifetime.Shared
{
    public class AdvancedComponentBase : OwningComponentBase, IAsyncComponentBase
    {
        [Parameter] public virtual RenderFragment ChildContent { get; set; }
        public RenderHandleAsync RenderChildContentAsync { get; set; }

        protected override async Task OnAfterRenderAsync(bool firstRender)
        {
            if (firstRender)
            {
                await OnComponentMountAsync().ConfigureAwait(false);
                if (RenderChildContentAsync != null)
                {
                    await RenderChildContentAsync();
                }
            }
            else
            {
                await Task.CompletedTask;
            }
        }

        protected virtual Task OnComponentMountAsync()
            => Task.CompletedTask;
    }
}