打造防止重复提交按钮

现在，我们就来改写AddAttributesToRender方法，ASP.NET在渲染该控件到输出时，会调用该方法我们所改写的方法，以达到将JS代码发送到客户端的目的。具体代码如下：

protected override void AddAttributesToRender(HtmlTextWriter writer)         {             System.Text.StringBuilder ClientSideEventReference = new System.Text.StringBuilder();             if (((this.Page != null) && this.CausesValidation) && (this.Page.Validators.Count > 0))             {                 ClientSideEventReference.Append("if (typeof(Page_ClientValidate) == 'function'){if (Page_ClientValidate() == false){return false;}}");             }             //ShowMessageBox?             if (this.ShowMessageBox)             {                 ClientSideEventReference.Append("if (!confirm('" + this.WarningText + "')){return false}");             }             ClientSideEventReference.AppendFormat("this.value = '{0}';", (string)this.ViewState["afterSubmitText"]);             ClientSideEventReference.Append("this.disabled = true;");             ClientSideEventReference.Append(this.Page.ClientScript.GetPostBackEventReference(this, string.Empty));             writer.AddAttribute(HtmlTextWriterAttribute.Onclick, ClientSideEventReference.ToString(), true);             base.AddAttributesToRender(writer);         }

我们把发送到客户端的js代码看作是一个字符串，为了提高性能，用StringBuilder来对象来构造这个字符串。
首先根据页面对象存在且控件启用了验证（该属性从父继承），且页面对象的验证器内计数大于0来决定输出一段引发验证的js代码，
根据ShowMessageBox属性来决定输出一个弹出提示的代码，并且弹出提示的内容由WarningText属性给出。
书写一个js脚本为按钮赋值为提交后文本，并且将按钮设置为禁用以变灰色。
最后附加一段由ASP.NET提供的用于影射回调事件引用的js脚本（this.Page.ClientScript.GetPostBackEventReference(this, string.Empty)方法将返回一个回送事件引用的js脚本字符串）

将StringBuilder对象内构造的字符串用HtmlTextWriter对象的AddAttribute方法写入按钮的OnClick事件中。

调用父类的AddAttributesToRender方法让父类有机会完成其他的配置等操作。


完整的ClickOnceButton代码如下：

using System; using System.Collections.Generic; using System.ComponentModel; using System.Text; using System.Web; using System.Web.UI; using System.Web.UI.WebControls; namespace BlogLan.Web.Controls {     /// <summary>     /// 表示一个防止重复提交的按钮。当用户单击按钮以后，该按钮变灰，不能再次单击，直到重新加载页面或者跳转。     /// </summary>     [DefaultProperty("Text")]     [ToolboxData("<{0}:ClickOnceButton runat=server></{0}:ClickOnceButton>")]     public class ClickOnceButton : System.Web.UI.WebControls.Button     {         /// <summary>         /// 默认的构造函数。         /// </summary>         public ClickOnceButton()         {             this.ViewState["afterSubmitText"] = "正在提交，请稍候...";             base.Text = "ClickOnceButton";             this.ViewState["showMessageBox"] = false;             this.ViewState["warningText"] = "确定要提交吗？";         }         /// <summary>         /// 获取或设置单击按钮后，按钮上所显示的文本。         /// </summary>         [Bindable(true),         Category("Appearance"),         DefaultValue("正在提交，请稍候..."),         Description("指示单击提交后，按钮上所显示的文本。")]         public string AfterSubmitText         {             get             {                 string afterSubmitText = (string)this.ViewState["afterSubmitText"];                 if (afterSubmitText != null)                 {                     return afterSubmitText;                 }                 else                 {                     return string.Empty;                 }             }             set             {                 this.ViewState["afterSubmitText"] = value;             }         }         [Bindable(true),         Category("Appearance"),         DefaultValue(false),         Description("指示是否要显示一个提示框。")]         public bool ShowMessageBox         {             get             {                 return (bool)this.ViewState["showMessageBox"];             }             set             {                 this.ViewState["showMessageBox"] = value;             }         }         [Bindable(true),         Category("Appearance"),         DefaultValue("确定要提交吗？"),         Description("指示提示框内所包含的内容。")]         public string WarningText         {             get             {                 return (string)this.ViewState["warningText"];             }             set             {                 this.ViewState["warningText"] = value;             }         }         /// <summary>         /// AddAttributesToRender         /// </summary>         /// <param name="writer">HtmlTextWriter</param>         protected override void AddAttributesToRender(HtmlTextWriter writer)         {             System.Text.StringBuilder ClientSideEventReference = new System.Text.StringBuilder();             if (((this.Page != null) && this.CausesValidation) && (this.Page.Validators.Count > 0))             {                 ClientSideEventReference.Append("if (typeof(Page_ClientValidate) == 'function'){if (Page_ClientValidate() == false){return false;}}");             }             //ShowMessageBox?             if (this.ShowMessageBox)             {                 ClientSideEventReference.Append("if (!confirm('" + this.WarningText + "')){return false}");             }             ClientSideEventReference.AppendFormat("this.value = '{0}';", (string)this.ViewState["afterSubmitText"]);             ClientSideEventReference.Append("this.disabled = true;");             ClientSideEventReference.Append(this.Page.ClientScript.GetPostBackEventReference(this, string.Empty));             writer.AddAttribute(HtmlTextWriterAttribute.Onclick, ClientSideEventReference.ToString(), true);             base.AddAttributesToRender(writer);         }     } }

你可以把它编译为dll，放置在工具箱中，随意拖放到网页上即可使用。因为继承了Button控件，它拥有Button的全部特性，并且自动继承了Button的设计时支持。