Net Core Filter

public class CategoryFilter : IActionFilter{
	CategoryRepository repository;
	public CategoryFilter(CategoryRepository repository) => this.repository = repository;
	public void OnActionExecuted(ActionExecutedContext context) { }
	public void OnActionExecuting(ActionExecutingContext context){
		if(context.Controller is Controller controller){
			controller.ViewBag.Categories = repository.GetCategories();
		}
	}
}

[TypeFilter<CategoryFilter>()]
public IActionResult Index(){
	return View();
}