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description title ms.date f1_keywords helpviewer_keywords ms.assetid
Learn more about: <add> Element for <listeners> for <source>
<add> Element for <listeners> for <source>
03/30/2017
initializeData attribute
add element for <listeners> for <source>
<add> element for <listeners> for <source>
4ce36ac1-81ef-48e8-b8b2-b5a5b0e2adcb

<add> Element for <listeners> for <source>

Adds a listener to the Listeners collection for a trace source.

<configuration>
  <system.diagnostics>
    <sources>
      <source>
        <listeners>
          <add>

Syntax

<add name="name"
  type="TraceListenerClassName, Version, Culture, PublicKeyToken"  
  initializeData="data"/>

Attributes and Elements

The following sections describe attributes, child elements, and parent elements.

Attributes

Attribute Description
type Required attribute, unless you're referencing a listener in the sharedListeners collection, in which case you only need to refer to it by name (see the Example).

Specifies the type of the listener. You must use a string that meets the requirements specified in Specifying Fully Qualified Type Names.
initializeData Optional attribute.

The string passed to the constructor for the specified class. A xref:System.Configuration.ConfigurationException is thrown if the class does not have a constructor that takes a string.
name Optional attribute.

Specifies the name of the listener.
traceOutputOptions Optional attribute.

Specifies the xref:System.Diagnostics.TraceListener.TraceOutputOptions%2A property value for the trace listener.
[custom attributes] Optional attributes.

Specifies the value for listener-specific attributes identified by the xref:System.Diagnostics.TraceListener.GetSupportedAttributes%2A method for that listener. xref:System.Diagnostics.DelimitedListTraceListener.Delimiter%2A is an example of an extra attribute unique to the xref:System.Diagnostics.DelimitedListTraceListener class.

Child Elements

Element Description
<filter> Adds a filter to a listener in the Listeners collection for a trace source.

Parent Elements

Element Description
configuration The root element in every configuration file used by the common language runtime and .NET Framework applications.
system.diagnostics Specifies trace listeners that collect, store, and route messages and the level where a trace switch is set.
sources Contains trace sources that initiate tracing messages.
source Specifies a trace source that initiates tracing messages.
listeners Specifies listeners that collect, store, and route messages.

Remarks

The listener classes shipped with the .NET Framework derive from the xref:System.Diagnostics.TraceListener class.

If you do not specify the name attribute of the trace listener, the xref:System.Diagnostics.TraceListener.Name%2A property of the trace listener defaults to an empty string (""). If your application has only one listener, you can add it without specifying a name, and you can remove it by specifying an empty string for the name. However, if your application has more than one listener, you should specify a unique name for each trace listener, which allows you to identify and manage individual trace listeners in the xref:System.Diagnostics.TraceSource.Listeners%2A?displayProperty=nameWithType collection.

Note

Adding more than one trace listener of the same type and with the same name results in only one trace listener of that type and name being added to the Listeners collection. However, you can programmatically add multiple identical listeners to the Listeners collection.

The value for the initializeData attribute depends on the type of listener you create. Not all trace listeners require that you specify initializeData.

Note

When you use the initializeData attribute, you may get the compiler warning "The 'initializeData' attribute is not declared." This warning occurs because the configuration settings are validated against the abstract base class xref:System.Diagnostics.TraceListener, which does not recognize the initializeData attribute. Typically, you can ignore this warning for trace listener implementations that have a constructor that takes a parameter.

The following table shows the trace listeners that are included with the .NET Framework and describes the value of their initializeData attributes.

Trace listener class initializeData attribute value
xref:System.Diagnostics.ConsoleTraceListener?displayProperty=nameWithType The useErrorStream value for the xref:System.Diagnostics.ConsoleTraceListener.%23ctor%2A constructor. Set the initializeData attribute to "true" to write trace and debug output to the standard error stream; set it to "false" to write to the standard output stream.
xref:System.Diagnostics.DelimitedListTraceListener?displayProperty=nameWithType The name of the file the xref:System.Diagnostics.DelimitedListTraceListener writes to.
xref:System.Diagnostics.EventLogTraceListener?displayProperty=nameWithType The name of an existing event log source.
xref:System.Diagnostics.EventSchemaTraceListener?displayProperty=nameWithType The name of the file that the xref:System.Diagnostics.EventSchemaTraceListener writes to.
xref:System.Diagnostics.TextWriterTraceListener?displayProperty=nameWithType The name of the file that the xref:System.Diagnostics.TextWriterTraceListener writes to.
xref:System.Diagnostics.XmlWriterTraceListener?displayProperty=nameWithType The name of the file that the xref:System.Diagnostics.XmlWriterTraceListener writes to.

Configuration File

This element can be used in the machine configuration file (Machine.config) and the application configuration file.

Example

The following example shows how to use <add> elements to add the listeners console and textListener to the Listeners collection for the trace source TraceSourceApp. The textListener listener writes trace output to the file myListener.log.

<configuration>  
  <system.diagnostics>  
    <sources>  
      <source name="TraceSourceApp" switchName="sourceSwitch"
        switchType="System.Diagnostics.SourceSwitch">  
        <listeners>  
          <add name="console"
            type="System.Diagnostics.ConsoleTraceListener"/>  
          <add name="textListener"/>  
          <remove name="Default"/>  
        </listeners>  
      </source>  
    </sources>  
    <sharedListeners>  
      <add name="textListener"
        type="System.Diagnostics.TextWriterTraceListener"
        initializeData="myListener.log"/>  
    </sharedListeners>  
    <switches>  
      <add name="sourceSwitch" value="Warning"/>  
    </switches>  
  </system.diagnostics>  
</configuration>

See also