探讨对Web控件的异常处理
在使用ASP.NET时,常常使用Page的错误事件Error进行错误捕捉和处理。这种方式可以集中处理所有异常,这种方式有利有弊。集中处理的好处就不用啰嗦了,这里只说明一下这种方式的局限,就是当页面中的某个控件发生异常之后,整个页面执行都会中断,然后处理异常,这样一来,页面就无法显示。
在实际开发中,常常有这样的需求,即页面是由多个相对独立的控件组成,其中一个控件的错误不能影响到其它控件的正常显示。这就需要在控件内部捕捉错误,并自行处理错误,然而控件基类并没有提供这样的错误捕捉功能。如何用简单有效方法来实现呢?
其实我们可以实现一个基类,并把所有在控件生命期中会调用到的方法都封装起来,这样只要继承这个控件,就可以方便地实现在控件内部自行捕捉错误的功能。请看下面的代码:
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public abstract class AbstractControl: Control
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{
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/// <summary>
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/// 异常栈
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/// </summary>
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public Stack Exceptions
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{
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get
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{
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if (exceptions == null)
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{
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exceptions = new Stack();
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}
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return exceptions;
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}
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}
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protected override void CreateChildControls()
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{
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try
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{
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CreateChildControlsByCatchedException();
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}
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catch (HttpUnhandledException)
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{
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throw;
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}
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catch (Exception ex)
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408_436_Open_Image.style.display='inline'; Codehighlighter1_408_436_Open_Text.style.display='inline';" src="/Images/OutliningIndicators/ContractedSubBlock.gif" align=top> {
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Exceptions.Push(ex);
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}
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}
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/// <summary>
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/// 创建子控件(已进行异常捕捉处理)
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/// </summary>
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protected virtual void CreateChildControlsByCatchedException()
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{
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}
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/// <summary>
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///
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/// </summary>
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/// <param name="e"></param>
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protected override void OnPreRender(EventArgs e)
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{
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try
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{
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OnPreRenderByCatchedException(e);
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}
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catch (HttpUnhandledException)
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{
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throw;
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}
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catch (Exception ex)
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{
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Exceptions.Push(ex);
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}
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}
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/// <summary>
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/// 呈现前事件(已进行错误捕捉处理)
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/// </summary>
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/// <param name="e"></param>
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protected virtual void OnPreRenderByCatchedException(EventArgs e)
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{
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base.OnPreRender (e);
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}
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/// <summary>
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/// 设计时的呈现前事件
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/// </summary>
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/// <param name="e"></param>
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protected virtual void DesigningOnPreRenderByCatchedException(EventArgs e)
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{
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}
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/// <summary>
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/// 呈现
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/// </summary>
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/// <param name="writer"></param>
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protected override void Render(HtmlTextWriter writer)
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{
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if (Exceptions.Count > 0)
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{
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while (Exceptions.Count > 0 )
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{
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Exception ex = (Exception) Exceptions.Pop();
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RenderException(writer, ex);
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}
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return;
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}
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try
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{
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RenderByCatchedException(writer);
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}
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catch (HttpUnhandledException)
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{
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throw;
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}
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catch (Exception ex)
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{
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RenderException(writer, ex);
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}
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}
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/// <summary>
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/// 呈现(已进行错误捕捉处理)
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/// </summary>
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/// <param name="writer"></param>
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protected virtual void RenderByCatchedException(HtmlTextWriter writer)
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{
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base.Render (writer);
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}
116![](https://www.cnblogs.com/Images/OutliningIndicators/InBlock.gif)
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/// <summary>
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/// 呈现异常
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/// </summary>
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/// <param name="writer"></param>
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/// <param name="ex"></param>
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private void RenderException(HtmlTextWriter writer, Exception ex)
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{
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writer.AddAttribute(HtmlTextWriterAttribute.Title, BuildExceptionInfomation(ex));
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writer.AddStyleAttribute("font-weight", "700");
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writer.AddStyleAttribute("color", "#f00");
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writer.AddStyleAttribute("border", "1px solid #ddd");
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writer.AddStyleAttribute("cursor", "pointer");
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writer.AddStyleAttribute("padding", "0px 3px 0px 3px");
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writer.AddStyleAttribute("background-color", "#ffe");
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writer.RenderBeginTag(HtmlTextWriterTag.Span);
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writer.Write("!");
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writer.RenderEndTag();
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}
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/// <summary>
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/// 生成异常信息
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/// </summary>
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/// <param name="ex"></param>
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/// <returns></returns>
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private string BuildExceptionInfomation(Exception ex)
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{
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StringBuilder sb = new StringBuilder();
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sb.Append(ex.Message);
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sb.Append(Environment.NewLine);
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sb.Append(ex.GetType().FullName);
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sb.Append(Environment.NewLine);
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sb.Append(ex.StackTrace);
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return sb.ToString();
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}
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/// <summary>
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/// 中断程序的执行
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/// </summary>
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/// <param name="ex"></param>
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protected virtual void Interrupt(Exception ex)
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{
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throw new HttpUnhandledException(ex.Message, ex);
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}
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}
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上面的代码只重载了OnPreRender、Render和CreateChildControls三个方法,实际上还有OnInit、OnLoad等,可以视实际需要而重载,这样重载之后,所有错误都被捕捉,并存放在错误栈中,并在呈现时将错误以某种格式呈现在界面上。注意,继承AbstractControl基类的控件应重载如RenderByCatchedException之类的方法。
如果某些错误不希望被捕捉,而是直接抛出到页面上,这时候还可以调用Interrupt方法来将错误直接抛出到页面上,并中断整个页面的执行。