How to create custom error reporting pages in ASP.NET by using Visual C# .NET

New features in ASP.NET

How to use the Page_Error method

1. Follow these steps to add a new file named PageEvent.aspx to your project:
   
   1. Open Microsoft Visual Studio .NET.
   2. In Solution Explorer, right-click the project node, point to Add, and then click Add Web Form.
   3. In the Name text box, type PageEvent.aspx, and then click Open.
2. Add the following code to PageEvent.aspx:

   <script language=C# runat="server">
   void Page_Load(object sender, System.EventArgs e)
   {
   throw(new ArgumentNullException());
   }
   
   public void Page_Error(object sender,EventArgs e)
   {
   Exception objErr = Server.GetLastError().GetBaseException();
   string err ="<b>Error Caught in Page_Error event</b><hr><br>" + 
   "<br><b>Error in: </b>" + Request.Url.ToString() +
   "<br><b>Error Message: </b>" + objErr.Message.ToString()+
   "<br><b>Stack Trace:</b><br>" + 
                     objErr.StackTrace.ToString();
   Response.Write(err.ToString());
   Server.ClearError();
   }
   </script> 
   

   
   Note In this code sample, the AutoEventWireup attribute is not explicitly set. If you do not explicitly assign a value to the AutoEventWireup attribute, the default value true is used. If you are using Visual Studio .NET to develop your applications, the Web Form template code explicitly sets the AutoEventWireup attribute value to false. There is an important difference between the default value that ASP.NET uses, and the default value that the Visual Studio .NET template code assigns to this attribute. If the AutoEventWireup attribute value is set to false, the event handlers that are declared in the .ASPX page do not fire. This may be confusing if you do not know about this functionality.
3. From the File menu, click Save PageEvent.aspx.
4. Right-click the page, and then click View in Browser to run the page. Notice that the error is thrown and reported according to the code specifications.

How to use the Application_Error method

1. Add a new file named AppEvent.aspx to your project.
2. Add the following code to AppEvent.aspx:

   <script language=C# runat="server">
   void Page_Load(object sender, System.EventArgs e)
   {
   throw(new ArgumentNullException());
   }
   </script>
   

   
   Note The information discussed in the "Page_Error" section about the AutoEventWireup attribute also applies to the code sample in this step. See the information in the "Page_Error" section for more details.
3. From the File menu, click Save AppEvent.aspx.
4. Add the Application_Error event handler to the Global.asax file to trap the error that you throw in the Page_Load event handler of the AppEvent.aspx page. Notice that you must add another using statement for the System.Diagnostics namespace to Global.asax to use the event log.
   
   Add the following code to the Global.asax file:

   using System.Diagnostics;
   
   protected void Application_Error(object sender, EventArgs e)
   {
   Exception objErr = Server.GetLastError().GetBaseException();
   string err ="Error Caught in Application_Error event\n" +
   "Error in: " + Request.Url.ToString() +
   "\nError Message:" + objErr.Message.ToString()+ 
   "\nStack Trace:" + objErr.StackTrace.ToString();
   EventLog.WriteEntry("Sample_WebApp",err,EventLogEntryType.Error);
   Server.ClearError();
   //additional actions...
   } 
   

5. Save the Global.asax file.
6. In Visual Studio .NET, on the Build menu, click Build.
7. Right-click the page, and then click View in Browser. In this case the page will be blank, however, you should notice that a new entry has been added in the event log. This sample makes an entry in the Application log, which is accessible from the Event Viewer. After logging the error you might want to redirect the user to another more user-friendly error page, or perform some additional actions if needed.

How to use the Web.config file

1. Open the Global.asax file from the previous example.
2. Comment out the Server.ClearError line to ensure that the error surfaces in the Web.config file.
3. Save your changes to Global.asax. Your code should now appear similar to the following:

   using System.Diagnostics;
   
   protected void Application_Error(object sender, EventArgs e)
   {
   Exception objErr = Server.GetLastError().GetBaseException();
   string err ="Error Caught in Application_Error event\n" +
   "Error in: " + Request.Url.ToString() +
   "\nError Message:" + objErr.Message.ToString() + 
   "\nStack Trace:" + objErr.StackTrace.ToString();
   EventLog.WriteEntry("Sample_WebApp",err,EventLogEntryType.Error);
   //Server.ClearError();
   //additional actions...
   } 
   

4. Add the following code to the <customErrors> section to redirect the user to a custom page:

   <customErrors defaultRedirect="http://hostName/applicationName/errorStatus.htm" mode="On">
   </customErrors>
   

   Note You must modify the file path in defaultRedirect attribute so that it references the relevant Web server and application names.
5. Because the errors that are trapped at this level are sent to a default error page, you must create an error page named ErrorStatus.htm. Keep in mind that you are using this method to control what is presented to the user, so this example uses an .htm page for the error page. Add the following code to ErrorStatus.htm:

   <HTML>
   <HEAD>
   <TITLE></TITLE>
   <META NAME="GENERATOR" Content="Microsoft Visual Studio 7.0">
   </HEAD>
   <BODY>
        <b>Custom Error page!</b>
        <br>
        You have been redirected here from the <customErrors> section of the 
        Web.config file.
   </BODY>
   </HTML>
   

6. To test the code, save the files, build the project, and then view AppEvent.aspx in the browser. Notice that when the error is thrown, you are redirected to the ErrorStatus.htm page.

<customErrors defaultRedirect="http://hostName/applicationName/errorStatus.htm" mode="On">
<error statusCode="404" redirect="filenotfound.htm" />
</customErrors>

• On: Unhandled exceptions redirect the user to the specified defaultRedirect page. This mode is used mainly in production.
• Off: Users receive the exception information and are not redirected to the defaultRedirect page. This mode is used mainly in development.
• RemoteOnly: Only users who access the site on the local computer (by using localhost) receive the exception information. All other users are redirected to the defaultRedirect page. This mode is used mainly for debugging.

Troubleshooting