public async Task <IActionResult> MarkCompleted(int?id) { if (id == null) { return(RedirectToAction("Error")); } if (!ModelState.IsValid) { return(RedirectToAction("Index")); } var task = await _repo.FindByIdAsync(id.Value); task.IsCompleted = true; await _repo.UpdateAsync(task); return(RedirectToAction("Index")); }