EventLog.WriteEvent Method (String, EventInstance, Byte[], Object[])

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

Writes an event log entry with the given event data, message replacement strings, and associated binary data, and using the specified registered event source.

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

Public Shared Sub WriteEvent ( _
	source As String, _
	instance As EventInstance, _
	data As Byte(), _
	ParamArray values As Object() _
Dim source As String
Dim instance As EventInstance
Dim data As Byte()
Dim values As Object()

EventLog.WriteEvent(source, instance, data, values)
public static void WriteEvent (
	String source, 
	EventInstance instance, 
	byte[] data, 
	Object[] values
public static function WriteEvent (
	source : String, 
	instance : EventInstance, 
	data : byte[], 
	... values : Object[]



The name of the event source registered for the application on the specified computer.


An EventInstance instance that represents a localized event log entry.


An array of bytes that holds the binary data associated with the entry.


An array of strings to merge into the message text of the event log entry.

Exception typeCondition


The source value is an empty string ("").

- or -

The source value is a null reference (Nothing in Visual Basic) (Nothing in Visual Basic).

- or -

instance.InstanceId is less than zero or greater than UInt16.MaxValue.

- or -

values has more than 256 elements.

- or -

One of the values elements is longer than 32766 bytes.

- or -

The source name results in a registry key path longer than 254 characters.


instance is a null reference (Nothing in Visual Basic) (Nothing in Visual Basic).


The registry key for the event log could not be opened.


The operating system reported an error when writing the event entry to the event log. A Windows error code is not available.

Use this method to write a localized entry with additional event-specific data to the event log, using a source already registered as an event source for the appropriate log. You specify the event properties with resource identifiers rather than string values. The Event Viewer uses the resource identifiers to display the corresponding strings from the localized resource file for the source. You must register the source with the corresponding resource file before you write events using resource identifiers.

The input instance instance specifies the event message and properties. Set the InstanceId of the instance input for the defined message in the source message resource file. You can optionally set the CategoryId and EntryType of the instance input to define the category and event type of your event entry. You can also specify an array of language-independent strings to insert into the localized message text. Set values to a null reference (Nothing in Visual Basic) (Nothing in Visual Basic) if the event message does not contain formatting placeholders for replacement strings.

Specify binary data with an event when it is necessary to provide additional details for the event. For example, use the data parameter to include information on a specific error. The Event Viewer does not interpret the associated event data; it displays the data in a combined hexadecimal and text format. Use event-specific data sparingly; include it only if you are sure it will be useful. You can also use event-specific data to store information the application can process independently of the Event Viewer. For example, you could write a viewer specifically for your events, or write a program that scans the event log and creates reports that include information from the event-specific data.

The specified source must be registered for an event log before using WriteEvent. The specified source must be configured for writing localized entries to the log; the source must at minimum have a message resource file defined.

You must create and configure the event source before writing the first entry with the source. Create the new event source during the installation of your application. This allows time for the operating system to refresh its list of registered event sources and their configuration. If the operating system has not refreshed its list of event sources, and you attempt to write an event with the new source, the write operation will fail. You can configure a new source using an EventLogInstaller, or using the CreateEventSource method. You must have administrative rights on the computer to create a new event source.

The source must be configured either for writing localized entries or for writing direct strings. Use the WriteEntry method if your application writes string values directly to the event log.

If your application writes entries using both resource identifiers and string values, you must register two separate sources. For example, configure one source with resource files, and then use that source in the WriteEvent method to write entries using resource identifiers to the event log. Then create a different source without resource files, and use that source in the WriteEntry method to write strings directly to the event log using that source.

The following example writes an informational event entry and a warning event entry to an existing event log. The event message text is specified using a resource identifier in a resource file. The example assumes the corresponding resource file has been registered for the source.

Dim sourceName As String = "SampleApplicationSource"
If EventLog.SourceExists(sourceName)
    ' Define an informational event and a warning event.

    ' The message identifiers correspond to the message text in the
    ' message resource file defined for the source.
    Dim myInfoEvent As EventInstance = new EventInstance(InformationMsgId, 0, EventLogEntryType.Information)
    Dim myWarningEvent As EventInstance = new EventInstance(WarningMsgId, 0, EventLogEntryType.Warning)

    ' Insert the method name into the event log message.
    Dim insertStrings() As String = {"EventLogSamples.WriteEventSample2"}

    ' Write the events to the event log.

    EventLog.WriteEvent(sourceName, myInfoEvent, insertStrings)

    ' Append binary data to the warning event entry.
    Dim binaryData() As Byte = { 7, 8, 9, 10 }
    EventLog.WriteEvent(sourceName, myWarningEvent, binaryData, insertStrings)
    Console.WriteLine("Warning - event source {0} not registered", _
End If

The example uses the following message text file, built into the resource library EventLogMsgs.dll. A message text file is the source from which the message resource file is created. The message text file defines the resource identifiers and text for the category, event message, and parameter insertion strings.

; // EventLogMsgs.mc
; // ********************************************************

; // Use the following commands to build this file:

; //   mc -s EventLogMsgs.mc
; //   rc EventLogMsgs.rc
; //   link /DLL /SUBSYSTEM:WINDOWS /NOENTRY /MACHINE:x86 EventLogMsgs.Res 
; // ********************************************************

; // - Event categories -
; // Categories must be numbered consecutively starting at 1.
; // ********************************************************


Database Query

Data Refresh

; // - Event messages -
; // *********************************

MessageId = 1000
Severity = Success
Facility = Application
My application message text, in English, for message id 1000, called from %1.

MessageId = 1001
Severity = Warning
Facility = Application
My application message text, in English, for message id 1001, called from %1.

MessageId = 1002
Severity = Success
Facility = Application
My generic information message in English, for message id 1002.

MessageId = 1003
Severity = Warning
Facility = Application
My generic warning message in English, for message id 1003, called from %1.

MessageId = 1004
Severity = Success
Facility = Application
The update cycle is complete for %%5002.

MessageId = 1005
Severity = Warning
Facility = Application
The refresh operation did not complete because the connection to server %1 could not be established.

; // - Event log display name -
; // ********************************************************

MessageId = 5001
Severity = Success
Facility = Application
Sample Event Log

; // - Event message parameters -
; //   Language independent insertion strings
; // ********************************************************

MessageId = 5002
Severity = Success
Facility = Application

Windows 98, Windows 2000 SP4, 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