How to: Determine If an Event Source Exists 

Once you identify a source for a particular event log, this information is stored in the server's registry files until you remove that source. If you try to re-register a source that has already been registered as a valid source for a given log, the system raises a run-time error. You can use the SourceExists method to determine whether or not a particular source has already been registered.

To determine if a source has already been registered

• Call the SourceExists method, specifying the source name to query.

  The following example shows how to determine if a source using the string MyApp1 is already registered, and to register it with the Application log if it is not.

  If Not EventLog.SourceExists("MyApp1") Then
      EventLog.CreateEventSource("MyApp1", "Application")
  End If
  

  if (!System.Diagnostics.EventLog.SourceExists("MyApp1"))
      System.Diagnostics.EventLog.CreateEventSource(
         "MyApp1", "Application");
  

  if (!System.Diagnostics.EventLog.SourceExists("MyApp1"))
  {
     System.Diagnostics.EventLog.CreateEventSource("MyApp1",
         "Application");
  }
  

  To determine if a source is registered on a remote computer, specify the computer name as a second parameter. The following code shows an example:

  If Not EventLog.SourceExists("MyApp1", "myserver") Then
      Dim create As New EventSourceCreationData("MyApp1", "Application")
      create.MachineName = "myserver"
      EventLog.CreateEventSource(create)
  End If
  

  EventSourceCreationData sourceData = new EventSourceCreationData("MyApp1", "Application");
  sourceData.MachineName = "myserver";
  if (!System.Diagnostics.EventLog.SourceExists("MyApp1", "myserver"))
      System.Diagnostics.EventLog.CreateEventSource(sourceData);
  

  if (!System.Diagnostics.EventLog.SourceExists("MyApp1", "myserver"))
  {
     System.Diagnostics.EventLog.CreateEventSource(
        "MyApp1", "Application", "myserver");
  }
  

See Also

Tasks

How to: Remove an Event Source
How to: Add Your Application as a Source of Event Log Entries
Walkthrough: Exploring Event Logs, Event Sources, and Entries