asp.net控制項開發基礎(2)

 一個有Onclick事件的button例子：

using System;
using System.Collections.Generic;
using System.Text;
using System.Web.UI;
using System.ComponentModel;

namespace ComponentControl
{
    [DefaultProperty("Text")]
    [ToolboxData("<{0}:MyButton runat=server></{0}:MyButton>")]
    public class Ctrl4 : Control, IPostBackEventHandler
    {
        public event EventHandler Click;//定義事件,EventHandler為系統委託名

        IPostBackEventHandler 成員IPostBackEventHandler 成員IPostBackEventHandler 成員#region IPostBackEventHandler 成員

        //該方法用於註冊事件
        public void RaisePostBackEvent(string eventArgument)
        {
            if (Click != null)
            {
                Click(this, EventArgs.Empty); //實現委託方法
            }
        }

        #endregion

        public string Text         //設定屬性Text的值
        {
            get { return ViewState["text"] == null ? "Button" : ViewState["text"].ToString(); }
            set { ViewState["text"] = value; }
        }

        protected override void Render(HtmlTextWriter writer)
        {
              writer.AddAttribute(HtmlTextWriterAttribute.Type, "Submit");
            writer.AddAttribute(HtmlTextWriterAttribute.Name, this.UniqueID);  //跟下面一句代碼實現同樣效果，觸發伺服器端事件，屬性必須是Name，不能為ID
            //writer.AddAttribute(HtmlTextWriterAttribute.Onclick, Page.GetPostBackEventReference(this));
            writer.AddAttribute(HtmlTextWriterAttribute.Value, Text);
            writer.RenderBeginTag(HtmlTextWriterTag.Input);
            writer.RenderEndTag();
            
            //writer.Write("<INPUT TYPE=submit name=" + this.UniqueID +" Value='Button' />");
        }
    }
}

另外一種最佳化的事件實現
EventHandlerList 類提供一個簡單的委託列表來添加和刪除委託,下面來看看更改後的代碼,
AddHandler有兩個參數事件對象和添加的委託,在OnClick事件中必須顯示將委託轉換為EventHandler類型

using System;
using System.Collections.Generic;
using System.Text;
using System.Web.UI;

namespace ComponentControl
{
    public class Ctrl5:Control,IPostBackEventHandler
    {
        // 聲明Click事件委託
        private static readonly object obj = new object();

        public virtual event EventHandler Click
        {
            add {
                Events.AddHandler(obj, value);
            }
            remove
            {
                Events.RemoveHandler(obj, value);
            }
        }

        protected override void Render(HtmlTextWriter writer)
        {
            writer.Write("<input type=submit name="+this.UniqueID+" value=Button />");
        }

        IPostBackEventHandler 成員IPostBackEventHandler 成員#region IPostBackEventHandler 成員

        public void RaisePostBackEvent(string eventArgument)
        {
            EventHandler child = (EventHandler)Events[obj];
            if (child != null)
                child(this, EventArgs.Empty);
        }

        #endregion
    }
}