如何构建自定义控件

public class SubHeader : WebControl   //一定要继承于WebControl且为public类
    {
    // The URL to navigate to in case the user is not registered
        private string _register = string.Empty;

        public SubHeader()   //在构造函数中定义其大小及样式
        {
            // Initialize default values
            this.Width = new Unit(100, UnitType.Percentage);
            this.CssClass = "SubHeader";
        }

        // Property to allow the user to define the URL for the registration page
        public string RegisterUrl
        {
            get { return _register; }
            set { _register = value; }
        }

        // This method is called when the control is being built
        //重写CreateChildControls方法，从而在此控件内添加其他控件，这样可封装在一起
        protected override void CreateChildControls()
        {
            // Clear any previously loaded controls一定要先清除自定义控件内的所有控件后，才能添加其他控件。
            this.Controls.Clear();
            Label lbl;
            HyperLink reg = new HyperLink();

            if (_register == string.Empty)
            {
                reg.NavigateUrl = Context.Request.ApplicationPath + 
                    Path.AltDirectorySeparatorChar + "Secure" + 
                    Path.AltDirectorySeparatorChar + "NewUser.aspx";
            } 
            else
            {
                reg.NavigateUrl = _register;
            }

            if (Context.User.Identity.IsAuthenticated)
            {
                reg.Text = "Edit my profile";
                reg.ToolTip = "Modify your personal information";
                HyperLink signout = new HyperLink();
                signout.NavigateUrl = Context.Request.ApplicationPath + 
                    Path.AltDirectorySeparatorChar + "Logout.aspx";
                signout.Text = "Logout";
                signout.ToolTip = "Leave the application";
                this.Controls.Add(new LiteralControl(" | "));
                this.Controls.Add(signout);
            }
            else 
                reg.Text = "Register";

            this.Controls.AddAt(0, reg);

            // Add it before the logout control if it was added 
            this.Controls.AddAt(0, reg);
            this.Controls.Add(new LiteralControl(" - "));

            // Add a label with the current data
            lbl = new Label();
            lbl.Text = DateTime.Now.ToLongDateString();
            this.Controls.Add(lbl);
        }
    }