EventInstance.CategoryId Property

Definition

Namespace:

System.Diagnostics

Assembly:

System.Diagnostics.EventLog.dll

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

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

public int CategoryId { get; set; }

member this.CategoryId : int with get, set

Public Property CategoryId As Integer

Property Value

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.

Exceptions

ArgumentOutOfRangeException

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

Examples

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 );
}

// 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 = new EventInstance(UpdateCycleCompleteMsgId, 0);

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

    // 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.
    EventLog.WriteEvent(sourceName, myEvent, Environment.MachineName);
}
else
{
    Console.WriteLine("Warning - event source {0} not registered",
        sourceName);
}

' Ensure that the source has already been registered using
' EventLogInstaller or EventLog.CreateEventSource.
Dim sourceName as String = "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.
    Dim myEvent As EventInstance = New EventInstance(UpdateCycleCompleteMsgId, 0)
    ' Write the event to the event log using the registered source.
    EventLog.WriteEvent(sourceName, myEvent)

    ' 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.
    EventLog.WriteEvent(sourceName, myEvent, Environment.MachineName)

Else 
    Console.WriteLine("Warning - event source {0} not registered", _
        sourceName)
End If

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  
.  

Remarks

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 article in the Platform SDK documentation. For details about defining event categories in resource files, see the "Event Categories" topic in the Platform SDK

See also

• WriteEvent
• CategoryNumber
• CategoryResourceFile
• CategoryResourceFile