MVP - Composition overview (See related posts)

public partial class ViewCustomers : System.Web.UI.Page, IViewCustomerView
{
	private ViewCustomerPresenter presenter;

	protected override void OnInit(EventArgs e)
    	{
        	base.OnInit(e);
        	presenter = new ViewCustomerPresenter(this);
        	this.customerDropDownList.SelectedIndexChanged += delegate
                                                                  {
                                                                  	presenter.DisplayCustomerDetails();
                                                              	  };
    	}

	// ...
}

public class ViewCustomerPresenter
{
	private readonly IViewCustomerView view;
	private readonly ICustomerTask task;

	public ViewCustomerPresenter(IViewCustomerView view) : this(view, new CustomerTask()) {}

        public ViewCustomerPresenter(IViewCustomerView view, ICustomerTask task)
        {
            this.view = view;
            this.task = task;
        }

        public void DisplayCustomerDetails()
        {
            int? customerId = SelectedCustomerId;

            if (customerId.HasValue)
            {
                CustomerDTO customer = task.GetDetailsForCustomer(customerId.Value);
                UpdateViewFrom(customer);
            }
        }

        private void UpdateViewFrom(CustomerDTO customer)
        {
            view.CompanyName = customer.CompanyName;
            view.ContactName = customer.ContactName;
            view.ContactTitle = customer.ContactTitle;
            view.Address = customer.Address;
            view.City = customer.City;
            view.Region = customer.Region;
            view.Country = customer.CountryOfResidence.Name;
            view.Phone = customer.Phone;
            view.Fax = customer.Fax;
            view.PostalCode = customer.PostalCode;
        }



	// ...
}

public class CustomerTask : ICustomerTask
{
	...
}