C#

induur wrote:

I can't modify the source codes of that external library

ExternalLibraryClass.ThemeChanged -= Yourhandler

induur wrote:

, but I have problems since the event is static

class ExternalLibraryProxy
{
     List<EventHandler> subscriptions = new List<EventHandler>();
     public event EventHandler ThemeChanged
     {
        add
        {
            ExternalLibrary.ThemeChanged += value;
            subscriptions.Add(value);
        }
        remove
        {
            ExternalLibrary.ThemeChanged -= value;
            subscriptions.Remove(value);
        }
     }

     public void ClearInvocationList()
     {
         foreach(EventHandler handler in subscriptions)
             ExternalLibrary.ThemeChanged -= handler;
         subscriptions.Clear();
     }
}

class ExternalLibrayProxy
{
   public event EventHandler ThemeChanged; // event which is mimicked
   public ExternalLibrayProxy(){
        ExternalLibray.ThemeChanged += EventHandlerMethod;
   }

   ~ExternalLibrayProxy(){
        ExternalLibray.ThemeChanged -= EventHandlerMethod;
   }

   void EventHandlerMethod(object sender,EventArgs args){
       if(ThemeChanged != null)
           ThemeChanged(sender,args);
   }
}