Handling Callback Exceptions on Server

Oct 29, 2020
7 minutes to read

You can use the static ASPxWebControl.CallbackError event to delegate callback exception handling to the Application_Error event handler (via the Web Application project’s Global.asax file), so that it handles all application-level errors (e.g., to log information on all errors). In the Global.asax file, add the following code to the Application_Start event handler. (Note that prior to version v10.2 of DevExpress ASP.NET controls, errors occurring on callback events could not be handled via the Application_Error event handler.)

C#
VB.NET

void Application_Start(object sender, EventArgs e) { 
    // Assign Application_Error as a callback error handler for DevExpress web controls
    ASPxWebControl.CallbackError += new EventHandler(Application_Error); 
}

Protected Sub Application_Start(ByVal sender As Object, ByVal e As EventArgs)
    AddHandler DevExpress.Web.ASPxWebControl.CallbackError, AddressOf ASPxWebControl_CallbackError
End Sub

Use the following code within the Application_Error event handler to obtain and log exception details:

C#
VB.NET

void Application_Error(object sender, EventArgs e) { 
    // ... 
    // Use HttpContext.Current to get a Web request processing helper 
    HttpServerUtility server = HttpContext.Current.Server; 
    Exception exception = server.GetLastError(); 
    // Log an exception 
    AddToLog(exception.Message, exception.StackTrace); 
}

Private Sub ASPxWebControl_CallbackError(ByVal sender As Object, ByVal e As EventArgs)
    ' ...  
    ' Use HttpContext.Current to get a Web request processing helper  
    Dim server As HttpServerUtility = HttpContext.Current.Server
    Dim exception As Exception = server.GetLastError()

    ' Log an exception  
    AddToLog(exception.Message, exception.StackTrace)
End Sub

Example

This example demonstrates how the ASPxWebControl.CallbackError server static event can be used within the Global.asax file to delegate handling of exceptions that occur during processing of DevExpress web control callbacks to the Application_Error event handler.

Note

A complete sample project is available at https://github.com/DevExpress-Examples/how-to-handle-app-level-errors-occurred-inside-aspnet-webforms-controls-during-callbacks-e2398

<?xml version="1.0"?>
<configuration>
  <configSections>
    <sectionGroup name="devExpress">
      <section name="themes" type="DevExpress.Web.ThemesConfigurationSection, DevExpress.Web.v14.2, Version=14.2.3.0, Culture=neutral, PublicKeyToken=b88d1754d700e49a" requirePermission="false" />
      <section name="compression" type="DevExpress.Web.CompressionConfigurationSection, DevExpress.Web.v14.2, Version=14.2.3.0, Culture=neutral, PublicKeyToken=b88d1754d700e49a" requirePermission="false" />
      <section name="settings" type="DevExpress.Web.SettingsConfigurationSection, DevExpress.Web.v14.2, Version=14.2.3.0, Culture=neutral, PublicKeyToken=b88d1754d700e49a" requirePermission="false" />
      <section name="errors" type="DevExpress.Web.ErrorsConfigurationSection, DevExpress.Web.v14.2, Version=14.2.3.0, Culture=neutral, PublicKeyToken=b88d1754d700e49a" requirePermission="false" />
    </sectionGroup>
  </configSections>
  <system.web>
    <compilation debug="true" targetFramework="4.0">
      <assemblies>
        <add assembly="DevExpress.Data.v14.2, Version=14.2.3.0, Culture=neutral, PublicKeyToken=B88D1754D700E49A" />
        <add assembly="DevExpress.Web.v14.2, Version=14.2.3.0, Culture=neutral, PublicKeyToken=B88D1754D700E49A" />
        <add assembly="DevExpress.Printing.v14.2.Core, Version=14.2.3.0, Culture=neutral, PublicKeyToken=B88D1754D700E49A" />
        <add assembly="System.Data.Linq, Version=4.0.0.0, Culture=neutral, PublicKeyToken=B77A5C561934E089" />
        <add assembly="System.Design, Version=4.0.0.0, Culture=neutral, PublicKeyToken=B03F5F7F11D50A3A" />
        <add assembly="System.Windows.Forms, Version=4.0.0.0, Culture=neutral, PublicKeyToken=B77A5C561934E089" />
      </assemblies>
    </compilation>
    <pages validateRequest="false">
    </pages>
    <customErrors redirectMode="ResponseRedirect" defaultRedirect="~/ErrorPage.aspx" mode="On">
      <error statusCode="500" redirect="~/ErrorPage.aspx" />
    </customErrors>
    <httpModules>
      <add type="DevExpress.Web.ASPxHttpHandlerModule, DevExpress.Web.v14.2, Version=14.2.3.0, Culture=neutral, PublicKeyToken=b88d1754d700e49a" name="ASPxHttpHandlerModule" />
    </httpModules>
    <httpHandlers>
      <add type="DevExpress.Web.ASPxHttpHandlerModule, DevExpress.Web.v14.2, Version=14.2.3.0, Culture=neutral, PublicKeyToken=b88d1754d700e49a" verb="GET" path="DX.ashx" validate="false" />
    </httpHandlers>
  </system.web>
  <system.webServer>
    <modules>
      <add type="DevExpress.Web.ASPxHttpHandlerModule, DevExpress.Web.v14.2, Version=14.2.3.0, Culture=neutral, PublicKeyToken=b88d1754d700e49a" name="ASPxHttpHandlerModule" />
    </modules>
    <validation validateIntegratedModeConfiguration="false" />
    <handlers>
      <add type="DevExpress.Web.ASPxHttpHandlerModule, DevExpress.Web.v14.2, Version=14.2.3.0, Culture=neutral, PublicKeyToken=b88d1754d700e49a" verb="GET" path="DX.ashx" name="ASPxHttpHandlerModule" preCondition="integratedMode" />
    </handlers>
  </system.webServer>
  <devExpress>
    <themes enableThemesAssembly="true" styleSheetTheme="" theme="" customThemeAssemblies="" />
    <compression enableHtmlCompression="false" enableCallbackCompression="true" enableResourceCompression="true" enableResourceMerging="true" />
    <settings doctypeMode="Xhtml" rightToLeft="false" embedRequiredClientLibraries="false" ieCompatibilityVersion="edge" />
    <errors callbackErrorRedirectUrl="~/ErrorPage.aspx" />
  </devExpress>
</configuration>

using System;
using System.Web;
using System.Web.UI;

public partial class _Default: Page {
    protected void Page_Load(object sender, EventArgs e) {
        if (HttpContext.Current.Session["Log"] == null)
            HttpContext.Current.Session["Log"] = "";
    }
    protected void CallbackControl_Callback(object source, DevExpress.Web.CallbackEventArgs e) {
        Exception innerException = new Exception("NoReport");
        throw new Exception("This Exception is thrown to demonstrate the ASPxWebControl.CallbackError Event.", innerException);
    }
}

<%@ Application Language="C#" %>
<%@ Import Namespace="System.IO" %>
<%@ Import Namespace="DevExpress.Web" %>

<script RunAt="server">
    void Application_Start(object sender, EventArgs e) {
        // Assign Application_Error as a callback error handler
        ASPxWebControl.CallbackError += new EventHandler(Application_Error);
    }

    void Application_Error(object sender, EventArgs e) {
        // Use HttpContext.Current to get a Web request processing helper
        HttpServerUtility server = HttpContext.Current.Server;
        Exception exception = server.GetLastError();
        if (exception is HttpUnhandledException)
            exception = exception.InnerException;
        // Log an exception
        AddToLog(exception.Message, exception.StackTrace);
    }

    void AddToLog(string message, string stackTrace) {
        StringBuilder sb = new StringBuilder();
        sb.AppendLine(DateTime.Now.ToLocalTime().ToString());
        sb.AppendLine(message);
        sb.AppendLine();
        sb.AppendLine("Source File: " + HttpContext.Current.Request.RawUrl);
        sb.AppendLine();
        sb.AppendLine("Stack Trace: ");
        sb.AppendLine(stackTrace);
        for (int i = 0; i < 150; i++)
            sb.Append("-");
        sb.AppendLine();
        HttpContext.Current.Session["Log"] += sb.ToString();
        sb.AppendLine();
    }
</script>

<%@ Page Language="C#" AutoEventWireup="true" CodeFile="Default.aspx.cs" Inherits="_Default" %>
<%@ Register Assembly="DevExpress.Web.v14.2" Namespace="DevExpress.Web" TagPrefix="dx" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
    <title></title>
</head>
<body>
    <form id="form1" runat="server">
    <dx:ASPxButton ID="Button" runat="server" Text="Throw Exception on Callback" AutoPostBack="False" Width="120px">
        <ClientSideEvents Click="function(s, e) { CallbackControl.PerformCallback(); }" />
    </dx:ASPxButton>
    <dx:ASPxCallback ID="CallbackControl" ClientInstanceName="CallbackControl" runat="server" OnCallback="CallbackControl_Callback">
    </dx:ASPxCallback>
    </form>
</body>
</html>

<%@ Page Language="C#" AutoEventWireup="true" CodeFile="ErrorPage.aspx.cs" Inherits="Default2" %>
<%@ Register Assembly="DevExpress.Web.v14.2" Namespace="DevExpress.Web" TagPrefix="dx" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
    <title></title>
</head>
<body>
    <form id="form1" runat="server">
    <asp:LinkButton ID="BackLinkButton" runat="server" Text="Back to Example" PostBackUrl="~/Default.aspx"></asp:LinkButton><br />
    <br />
    Error log:
    <dx:ASPxMemo ID="Memo" runat="server" Height="500px" Width="100%">
    </dx:ASPxMemo>
    <asp:LinkButton ID="ClearLinkButton" runat="server" Text="Clear" OnClick="ClearLinkButton_Click"></asp:LinkButton>
    </form>
</body>
</html>

using System;
using System.Web;

public partial class Default2: System.Web.UI.Page {
    protected void Page_Load(object sender, EventArgs e) {
        if (HttpContext.Current.Session["Log"] != null)
            Memo.Text = HttpContext.Current.Session["Log"].ToString();
    }
    protected void ClearLinkButton_Click(object sender, EventArgs e) {
        HttpContext.Current.Session["Log"] = "";
        Memo.Text = "";
    }
}

<%@ Page Language="vb" AutoEventWireup="true" CodeFile="Default.aspx.vb" Inherits="_Default" %>
<%@ Register Assembly="DevExpress.Web.v14.2" Namespace="DevExpress.Web" TagPrefix="dx" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
    <title></title>
</head>
<body>
    <form id="form1" runat="server">
    <dx:ASPxButton ID="Button" runat="server" Text="Throw Exception on Callback" AutoPostBack="False" Width="120px">
        <ClientSideEvents Click="function(s, e) { CallbackControl.PerformCallback(); }" />
    </dx:ASPxButton>
    <dx:ASPxCallback ID="CallbackControl" ClientInstanceName="CallbackControl" runat="server" OnCallback="CallbackControl_Callback">
    </dx:ASPxCallback>
    </form>
</body>
</html>

Imports System
Imports System.Web

Partial Public Class Default2
    Inherits System.Web.UI.Page

    Protected Sub Page_Load(ByVal sender As Object, ByVal e As EventArgs)
        If HttpContext.Current.Session("Log") IsNot Nothing Then
            Memo.Text = HttpContext.Current.Session("Log").ToString()
        End If
    End Sub
    Protected Sub ClearLinkButton_Click(ByVal sender As Object, ByVal e As EventArgs)
        HttpContext.Current.Session("Log") = ""
        Memo.Text = ""
    End Sub
End Class

<%@ Page Language="vb" AutoEventWireup="true" CodeFile="ErrorPage.aspx.vb" Inherits="Default2" %>
<%@ Register Assembly="DevExpress.Web.v14.2" Namespace="DevExpress.Web" TagPrefix="dx" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
    <title></title>
</head>
<body>
    <form id="form1" runat="server">
    <asp:LinkButton ID="BackLinkButton" runat="server" Text="Back to Example" PostBackUrl="~/Default.aspx"></asp:LinkButton><br />
    <br />
    Error log:
    <dx:ASPxMemo ID="Memo" runat="server" Height="500px" Width="100%">
    </dx:ASPxMemo>
    <asp:LinkButton ID="ClearLinkButton" runat="server" Text="Clear" OnClick="ClearLinkButton_Click"></asp:LinkButton>
    </form>
</body>
</html>

<?xml version="1.0"?>
<configuration>
  <configSections>
    <sectionGroup name="devExpress">
      <section name="themes" type="DevExpress.Web.ThemesConfigurationSection, DevExpress.Web.v14.2, Version=14.2.3.0, Culture=neutral, PublicKeyToken=b88d1754d700e49a" requirePermission="false" />
      <section name="compression" type="DevExpress.Web.CompressionConfigurationSection, DevExpress.Web.v14.2, Version=14.2.3.0, Culture=neutral, PublicKeyToken=b88d1754d700e49a" requirePermission="false" />
      <section name="settings" type="DevExpress.Web.SettingsConfigurationSection, DevExpress.Web.v14.2, Version=14.2.3.0, Culture=neutral, PublicKeyToken=b88d1754d700e49a" requirePermission="false" />
      <section name="errors" type="DevExpress.Web.ErrorsConfigurationSection, DevExpress.Web.v14.2, Version=14.2.3.0, Culture=neutral, PublicKeyToken=b88d1754d700e49a" requirePermission="false" />
    </sectionGroup>
  </configSections>
  <system.web>
    <compilation debug="true" targetFramework="4.0">
      <assemblies>
        <add assembly="DevExpress.Data.v14.2, Version=14.2.3.0, Culture=neutral, PublicKeyToken=B88D1754D700E49A" />
        <add assembly="DevExpress.Web.v14.2, Version=14.2.3.0, Culture=neutral, PublicKeyToken=B88D1754D700E49A" />
        <add assembly="DevExpress.Printing.v14.2.Core, Version=14.2.3.0, Culture=neutral, PublicKeyToken=B88D1754D700E49A" />
        <add assembly="System.Data.Linq, Version=4.0.0.0, Culture=neutral, PublicKeyToken=B77A5C561934E089" />
        <add assembly="System.Design, Version=4.0.0.0, Culture=neutral, PublicKeyToken=B03F5F7F11D50A3A" />
        <add assembly="System.Windows.Forms, Version=4.0.0.0, Culture=neutral, PublicKeyToken=B77A5C561934E089" />
      </assemblies>
    </compilation>
    <pages validateRequest="false">
    </pages>
    <customErrors redirectMode="ResponseRedirect" defaultRedirect="~/ErrorPage.aspx" mode="On">
      <error statusCode="500" redirect="~/ErrorPage.aspx" />
    </customErrors>
    <httpModules>
      <add type="DevExpress.Web.ASPxHttpHandlerModule, DevExpress.Web.v14.2, Version=14.2.3.0, Culture=neutral, PublicKeyToken=b88d1754d700e49a" name="ASPxHttpHandlerModule" />
    </httpModules>
    <httpHandlers>
      <add type="DevExpress.Web.ASPxHttpHandlerModule, DevExpress.Web.v14.2, Version=14.2.3.0, Culture=neutral, PublicKeyToken=b88d1754d700e49a" verb="GET" path="DX.ashx" validate="false" />
    </httpHandlers>
  </system.web>
  <system.webServer>
    <modules>
      <add type="DevExpress.Web.ASPxHttpHandlerModule, DevExpress.Web.v14.2, Version=14.2.3.0, Culture=neutral, PublicKeyToken=b88d1754d700e49a" name="ASPxHttpHandlerModule" />
    </modules>
    <validation validateIntegratedModeConfiguration="false" />
    <handlers>
      <add type="DevExpress.Web.ASPxHttpHandlerModule, DevExpress.Web.v14.2, Version=14.2.3.0, Culture=neutral, PublicKeyToken=b88d1754d700e49a" verb="GET" path="DX.ashx" name="ASPxHttpHandlerModule" preCondition="integratedMode" />
    </handlers>
  </system.webServer>
  <devExpress>
    <themes enableThemesAssembly="true" styleSheetTheme="" theme="" customThemeAssemblies="" />
    <compression enableHtmlCompression="false" enableCallbackCompression="true" enableResourceCompression="true" enableResourceMerging="true" />
    <settings doctypeMode="Xhtml" rightToLeft="false" embedRequiredClientLibraries="false" ieCompatibilityVersion="edge" />
    <errors callbackErrorRedirectUrl="~/ErrorPage.aspx" />
  </devExpress>
</configuration>

<%@ Application Language="vb" %>
<%@ Import Namespace="System.IO" %>
<%@ Import Namespace="DevExpress.Web" %>

<script RunAt="server">
    Sub Application_Start(ByVal sender As Object, ByVal e As EventArgs)
        ' Assign Application_Error as a callback error handler
        AddHandler ASPxWebControl.CallbackError, AddressOf Application_Error
    End Sub

    Sub Application_Error(ByVal sender As Object, ByVal e As EventArgs)
        ' Use HttpContext.Current to get a Web request processing helper
        Dim exception As Exception = HttpContext.Current.Server.GetLastError()
        If TypeOf exception Is HttpUnhandledException Then
            exception = exception.InnerException
        End If
        ' Log an exception
        AddToLog(exception.Message, exception.StackTrace)
    End Sub

    Sub AddToLog(ByVal message As String, ByVal stackTrace As String)
        Dim sb As New StringBuilder()
        sb.AppendLine(Date.Now.ToLocalTime().ToString())
        sb.AppendLine(message)
        sb.AppendLine()
        sb.AppendLine("Source File: " & HttpContext.Current.Request.RawUrl)
        sb.AppendLine()
        sb.AppendLine("Stack Trace: ")
        sb.AppendLine(stackTrace)
        For i As Integer = 0 To 149
            sb.Append("-")
        Next i
        sb.AppendLine()
        HttpContext.Current.Session("Log") += sb.ToString()
        sb.AppendLine()
    End Sub
</script>

Imports System
Imports System.Web
Imports System.Web.UI

Partial Public Class _Default
    Inherits Page

    Protected Sub Page_Load(ByVal sender As Object, ByVal e As EventArgs)
        If HttpContext.Current.Session("Log") Is Nothing Then
            HttpContext.Current.Session("Log") = ""
        End If
    End Sub
    Protected Sub CallbackControl_Callback(ByVal source As Object, ByVal e As DevExpress.Web.CallbackEventArgs)
        Dim innerException As New Exception("NoReport")
        Throw New Exception("This Exception is thrown to demonstrate the ASPxWebControl.CallbackError Event.", innerException)
    End Sub
End Class

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