Effective C# 原則 22：用事件定義對外介面（三）

事件記錄器實作範例

另一個類別直接輸出到系統事件日誌：

class EventLogger
{
    private static string eventSource;
    private static EventLog logDest;
    static EventLogger()
    {
        logger.Log += new AddMessageEventHandler(Event_Log);
    }
    public static string EventSource
    {
        get { return eventSource; }
        set
        {
            eventSource = value;
            if (!EventLog.SourceExists(eventSource))
                EventLog.CreateEventSource(eventSource, "ApplicationEventLogger");
            if (logDest != null) logDest.Dispose();
            logDest = new EventLog();
            logDest.Source = eventSource;
        }
    }
    private static void Event_Log(object sender, LoggerEventArgs msg)
    {
        if (logDest != null)
            logDest.WriteEntry(msg.Message, EventLogEntryType.Information, msg.Priority);
    }
}