event - object referance is not set to an instanse of an object windows forms C# -

i trying raise event in dll file refrenced windows forms project.

i have following message when run program "object not set instace of object":

namespace server {

public delegate void messagehnadler();   public class classserver {       public event messagehnadler messageforchat         public string message { get; set; }      public socket listenersocket;     public binaryformatter transbinary;      public thread threadingserver;     public tcplistener listenerserver;         private list<tcpclient> connectedclients = new list<tcpclient>();       public bool openserver(string ipaddress, int portnumber)     {          try         {             listenerserver = new tcplistener(ipaddress.parse(ipaddress), portnumber);//creating listener clients connect              listenerserver.start();              threadingserver = new thread(loopthroughclients);             threadingserver.start();              threadingserver = new thread(getmessage);             threadingserver.start();               return true;         }         catch (exception)         {              return false;         }     }      public void loopthroughclients()     {         listenersocket = listenerserver.acceptsocket();      }        public void getmessage()     {         while (true)         {             if (listenersocket != null)             {                 networkstream streamwithclient = new networkstream(listenersocket);                 transbinary = new binaryformatter();                 string stringfromclient = (string)transbinary.deserialize(streamwithclient);                 if (stringfromclient != null)                 {                     message = stringfromclient;                     messageforchat();                 }                  streamwithclient = new networkstream(listenersocket);                 binaryformatter tranbinary = new binaryformatter();                   tranbinary.serialize(streamwithclient, stringfromclient);                 stringfromclient = null;             }         }     } 

in windows forms project signed event function:

namespace chat_project_server_ui { public partial class severui : form { openserverform openserver = new openserverform(); classserver serverforevent = new classserver();

    public severui()     {         initializecomponent();          openserver.showdialog();          serverforevent.messageforchat += new messagehnadler(serverforevent_messageforchat);            openningserver();       }      public void openningserver()     {           if(openserver.isconnected)         {             chattextbox.appendtext("server open!\n");         }         else         {             chattextbox.appendtext("faild open server...\n");         }      }     private void test_click(object sender, eventargs e)     {          chattextbox.appendtext("aaaaa");      }      public void eventholder()     {      }      void serverforevent_messageforchat()     {         chattextbox.appendtext(serverforevent.message);      }    } 

always check if handler has been assigned first follows:

var handler = messageforchat; if (handler != null)     handler()