TraceSource Class

Note: This class is new in the .NET Framework version 2.0.

Provides a set of methods and properties that enable applications to trace the execution of code and associate trace messages with their source.

Namespace: System.Diagnostics
Assembly: System (in system.dll)

public class TraceSource
public class TraceSource
public class TraceSource

The TraceSource class is used by applications to produce traces that can be associated with the application. TraceSource provides tracing methods that allow you to easily trace events, trace data, and issue informational traces. Trace output from TraceSource can be controlled by configuration file settings. The configuration file is located in the folder with the application executable and has the name of the application with the .config file name extension added. For example, the name of the configuration file for TraceSourceSample.exe is TraceSourceSample.exe.config. The configuration file can be used to determine where the trace information is to be sent and what levels of activity are to be traced. The following example shows the contents of a sample application configuration file.

      <source name="TraceTest" switchName="SourceSwitch" 
        switchType="System.Diagnostics.SourceSwitch" >
          <add name="console" />
          <remove name ="Default" />
      <!-- You can set the level at which tracing is to occur -->
      <add name="SourceSwitch" value="Warning" />
        <!-- You can turn tracing off -->
        <!--add name="SourceSwitch" value="Off" -->
      <add name="console" 
    <trace autoflush="true" indentsize="4">
        <add name="console" />

The TraceSource class is identified by the name of a source, typically the name of the application. The trace messages coming from a particular component can be initiated by a particular trace source, allowing all messages coming from that component to be easily identified.

TraceSource defines tracing methods but does not actually provide any specific mechanism for generating and storing tracing data. The tracing data is produced by trace listeners, which are plug-ins that can be loaded by trace sources.

You can customize the tracing output's target by adding or removing TraceListener instances to or from the collection stored in the TraceSource.Listeners property. By default, trace output is produced using an instance of the DefaultTraceListener class. The preceding configuration file example demonstrates removing the DefaultTraceListener and adding a ConsoleTraceListener to produce the trace output for the trace source. For more information, see <listeners> Element for <source> and <sharedListeners> Element.

The SourceSwitch class provides the means to dynamically control the tracing output. The preceding configuration file example shows how you can turn off tracing from a trace source and control the level at which tracing occurs. You can modify the value of the source switch without recompiling your application. For information on using the configuration file to set a switch, see Switch and How to: Configure Trace Switches.


If you modify a configuration file while an application is executing, the application must be stopped and restarted or the Refresh method must be called before the new settings take effect.

The TraceEventType enumeration is used to define the event type of the trace message. Trace filters use the TraceEventType to determine if a trace listener should produce the trace message.

The trace listeners can optionally have an additional layer of filtering through a trace filter. If a trace listener has an associated filter, the listener calls the ShouldTrace method on that filter to determine whether or not to produce the trace information.

The trace listeners use the values of the Trace class properties Indent, IndentSize, and AutoFlush to format trace output. You can use configuration file attributes to set the Indent, IndentSize, and AutoFlush properties. The following example sets the AutoFlush property to false and the IndentSize property to 3.

    <trace autoflush="false" indentsize="3" />

The following code example shows the use of the TraceSource class to forward traces to listeners. The example also demonstrates switch and filter usage.

// The following configuration file can be used with this sample.
// When using a configuration file #define ConfigFile.
//    <system.diagnostics>
//        <sources>
//            <source name="TraceTest" switchName="SourceSwitch" switchType="System.Diagnostics.SourceSwitch" >
//                <listeners>
//                    <add name="console" type="System.Diagnostics.ConsoleTraceListener" initializeData="false" />
//                    <remove name ="Default" />
//                </listeners>
//            </source>
//        </sources>
//        <switches>
//            <!-- You can set the level at which tracing is to occur -->
//            <add name="SourceSwitch" value="Warning" />
//            <!-- You can turn tracing off -->
//            <!--add name="SourceSwitch" value="Off" -->
//        </switches>
//        <trace autoflush="true" indentsize="4"></trace>
//    </system.diagnostics>
#define TRACE
#define ConfigFile

using System;
using System.Collections;
using System.Diagnostics;
using System.Reflection;
using System.IO;
using System.Security.Permissions;

namespace Testing
    class TraceTest
        // Initialize the trace source.
        static TraceSource ts = new TraceSource("TraceTest");
        [SwitchAttribute("SourceSwitch", typeof(SourceSwitch))]
        static void Main()
                // Initialize trace switches.
                SourceSwitch sourceSwitch = new SourceSwitch("SourceSwitch", "Verbose");
                ts.Listeners["console"].TraceOutputOptions |= TraceOptions.Callstack;
                ts.TraceEvent(TraceEventType.Warning, 1);
                ts.Listeners["console"].TraceOutputOptions = TraceOptions.DateTime;
                // Issue file not found message as a warning.
                ts.TraceEvent(TraceEventType.Warning, 2, "File Test not found");
                // Issue file not found message as a verbose event using a formatted string.
                ts.TraceEvent(TraceEventType.Verbose, 3, "File {0} not found.", "test");
                // Issue file not found message as information.
                ts.TraceInformation("File {0} not found.", "test");
                ts.Listeners["console"].TraceOutputOptions |= TraceOptions.LogicalOperationStack;
                // Issue file not found message as an error event.
                ts.TraceEvent(TraceEventType.Error, 4, "File {0} not found.", "test");
                // Test the filter on the ConsoleTraceListener.
                ts.Listeners["console"].Filter = new SourceFilter("No match");
                ts.TraceData(TraceEventType.Error, 5,
                    "SourceFilter should reject this message for the console trace listener.");
                ts.Listeners["console"].Filter = new SourceFilter("TraceTest");
                ts.TraceData(TraceEventType.Error, 6,
                    "SourceFilter should let this message through on the console trace listener.");
                ts.Listeners["console"].Filter = null;
                // Use the TraceData method. 
                ts.TraceData(TraceEventType.Warning, 7, new object());
                ts.TraceData(TraceEventType.Warning, 8, new object[] { "Message 1", "Message 2" });
                // Activity tests.
                ts.TraceEvent(TraceEventType.Start, 9, "Will not appear until the switch is changed.");
                ts.Switch.Level = SourceLevels.ActivityTracing | SourceLevels.Critical;
                ts.TraceEvent(TraceEventType.Suspend, 10, "Switch includes ActivityTracing, this should appear");
                ts.TraceEvent(TraceEventType.Critical, 11, "Switch includes Critical, this should appear");
                Console.WriteLine("Press any key to exit.");
            catch (Exception e)
                // Catch any unexpected exception.
                Console.WriteLine("Unexpected exception: " + e.ToString());
        public static void DisplayProperties(TraceSource ts)
            Console.WriteLine("SourceSwitch name = " + ts.Name);
            Console.WriteLine("TraceSource switch level = " + ts.Switch.Level);
            Console.WriteLine("TraceSource switch = " + ts.Switch.DisplayName);
            SwitchAttribute[] switches = SwitchAttribute.GetAll(Assembly.GetExecutingAssembly());
            for (int i = 0; i < switches.Length; i++)
                Console.WriteLine("Switch name = " + switches[i].SwitchName);
                Console.WriteLine("Switch type = " + switches[i].SwitchType);
            // Get the custom attributes for the TraceSource.
            Console.WriteLine("Number of custom trace source attributes = "
                + ts.Attributes.Count);
            foreach (DictionaryEntry de in ts.Attributes)
                Console.WriteLine("Custom trace source attribute = "
                    + de.Key + "  " + de.Value);
            // Get the custom attributes for the trace source switch.
            foreach (DictionaryEntry de in ts.Switch.Attributes)
                Console.WriteLine("Custom switch attribute = "
                    + de.Key + "  " + de.Value);
            Console.WriteLine("Number of listeners = " + ts.Listeners.Count);
            foreach (TraceListener traceListener in ts.Listeners)
                Console.Write("TraceListener: " + traceListener.Name + "\t");
                // The following output can be used to update the configuration file.
                Console.WriteLine("AssemblyQualifiedName = " +


Any public static (Shared in Visual Basic) members of this type are thread safe. Any instance members are not guaranteed to be thread safe.

Windows 98, Windows 2000 SP4, Windows Millennium Edition, Windows Server 2003, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP SP2, Windows XP Starter Edition

The .NET Framework does not support all versions of every platform. For a list of the supported versions, see System Requirements.

.NET Framework

Supported in: 2.0