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EventInstance::CategoryId Property

Gets or sets the resource identifier that specifies the application-defined category of the event entry.

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

public:
property int CategoryId {
	int get ();
	void set (int value);
}

Property Value

Type: System::Int32
A numeric category value or resource identifier that corresponds to a string defined in the category resource file of the event source. The default is zero, which signifies that no category will be displayed for the event entry.

ExceptionCondition
ArgumentOutOfRangeException

The property is set to a negative value or to a value larger than UInt16::MaxValue.

Event log categories are application-defined values that help filter events, or provide further information about the event. For example, your application can define separate categories for different components or different operations.

Set the CategoryId property to specify the category that the Event Viewer displays for the entry. The Event Viewer can display the category as a numeric value, or it can use the CategoryId as a resource identifier to display a localized category string based on the current language settings.

To display localized category strings in the Event Viewer, you must use an event source configured with a category resource file, and set the CategoryId to a resource identifier in the category resource file. If the event source does not have a configured category resource file, or the specified CategoryId does not index a string in the category resource file, and then the Event Viewer displays the numeric category value for that entry.

You must register the source with the corresponding resource file before you write event categories using resource identifiers. Configure the category resource file, along with the number of category strings in the resource file, using the EventLogInstaller or the EventSourceCreationData class. When defining category strings in a resource file, the category resource identifiers must be numbered consecutively starting at 1, up to the configured CategoryCount property value.

Event categories are optional. If your application does not use categories, do not set the CategoryId for the event log entry.

For details about defining event messages and building event resource files, see the "Message Compiler" topic in the Platform SDK documentation at http://msdn.microsoft.com. For details about defining event categories in resource files, see the "Event Categories" topic in the Platform SDK

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

// Ensure that the source has already been registered using 
// EventLogInstaller or EventLog.CreateEventSource.
String^ sourceName = "SampleApplicationSource";
if ( EventLog::SourceExists( sourceName ) )
{
   // Define an informational event with no category. 
   // The message identifier corresponds to the message text in the 
   // message resource file defined for the source.
   EventInstance ^ myEvent = gcnew EventInstance( UpdateCycleCompleteMsgId,0 );

   // Write the event to the event log using the registered source.
   EventLog::WriteEvent( sourceName, myEvent, 0 );

   // Reuse the event data instance for another event entry. 
   // Set the entry category and message identifiers for 
   // the appropriate resource identifiers in the resource files 
   // for the registered source.  Set the event type to Warning.
   myEvent->CategoryId = RefreshCategoryMsgId;
   myEvent->EntryType = EventLogEntryType::Warning;
   myEvent->InstanceId = ServerConnectionDownMsgId;

   // Write the event to the event log using the registered source. 
   // Insert the machine name into the event message text. 
   array<String^>^ss = {Environment::MachineName};
   EventLog::WriteEvent( sourceName, myEvent, ss );
}
else
{
   Console::WriteLine( "Warning - event source {0} not registered", sourceName );
}

The code 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.
; // ********************************************************

MessageId=0x1
Severity=Success
SymbolicName=INSTALL_CATEGORY
Language=English
Installation
.

MessageId=0x2
Severity=Success
SymbolicName=QUERY_CATEGORY
Language=English
Database Query
.

MessageId=0x3
Severity=Success
SymbolicName=REFRESH_CATEGORY
Language=English
Data Refresh
.

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

MessageId = 1000
Severity = Success
Facility = Application
SymbolicName = AUDIT_SUCCESS_MESSAGE_ID_1000
Language=English
My application message text, in English, for message id 1000, called from %1.
.

MessageId = 1001
Severity = Warning
Facility = Application
SymbolicName = AUDIT_FAILED_MESSAGE_ID_1001
Language=English
My application message text, in English, for message id 1001, called from %1.
.


MessageId = 1002
Severity = Success
Facility = Application
SymbolicName = GENERIC_INFO_MESSAGE_ID_1002
Language=English
My generic information message in English, for message id 1002.
.


MessageId = 1003
Severity = Warning
Facility = Application
SymbolicName = GENERIC_WARNING_MESSAGE_ID_1003
Language=English
My generic warning message in English, for message id 1003, called from %1.
.


MessageId = 1004
Severity = Success
Facility = Application
SymbolicName = UPDATE_CYCLE_COMPLETE_MESSAGE_ID_1004
Language=English
The update cycle is complete for %%5002.
.


MessageId = 1005
Severity = Warning
Facility = Application
SymbolicName = SERVER_CONNECTION_DOWN_MESSAGE_ID_1005
Language=English
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
SymbolicName = EVENT_LOG_DISPLAY_NAME_MSGID
Language=English
Sample Event Log
.



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


MessageId = 5002
Severity = Success
Facility = Application
SymbolicName = EVENT_LOG_SERVICE_NAME_MSGID
Language=English
SVC_UPDATE.EXE
.

.NET Framework

Supported in: 4.5, 4, 3.5, 3.0, 2.0

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

Windows 8.1, Windows Server 2012 R2, Windows 8, Windows Server 2012, Windows 7, Windows Vista SP2, Windows Server 2008 (Server Core Role not supported), Windows Server 2008 R2 (Server Core Role supported with SP1 or later; Itanium not supported)

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

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