Problem getting events from C# to VJ++

From: Jeff Van Epps (jve86_at_lordbah.com)
Date: 11/12/04 

Date: 12 Nov 2004 04:53:45 -0800

We've been unable to get events working going from C# to VJ++. We
think that the C# component is being exposed properly as a
ConnectionPoint, and the Advise() from the VJ++ side seems to be
working, because the delegate on the C# side has 1 item in its
invocation list after the Advise(). However when we try to make the
callback, we get:

System.NullReferenceException: Object reference not set to an instance
of an object
  at System.RuntimeType.InvokeDispMethod(String name, BindingFlags
invokeAttr, Object target, Object[] args, Boolean[] byrefModifiers,
Int32 culture, String[] namedParameters)
   at System.RuntimeType.InvokeMember(String name, BindingFlags
invokeAttr, Binder binder, Object target, Object[] args,
ParameterModifier[] modifiers, CultureInfo culture, String[]
namedParameters)
   at System.RuntimeType.ForwardCallToInvokeMember(String memberName,
BindingFlags flags, Object target, Int32[] aWrapperTypes, MessageData&
msgData)
   at IWeatherEvents.OnWeatherChanged(Int32 nTemperature)
   at TemperatureComponent.StateChange(Object sender, EventArgs args)
   at System.Windows.Forms.Timer.OnTick(EventArgs e)
   at System.Windows.Forms.Timer.DebuggableCallback(IntPtr hWnd, Int32
msg, IntPtr idEvent, IntPtr dwTime)

We'd appreciate help. We have a significant code base of VJ++ and
we've determined that the JCLA has too many issues, so we're going to
have to be hybrid for a little while. I think this is supposed to
work.

ITemp.idl
---------
/////

import "oaidl.idl";

 interface ITemp; // defined below
 interface IWeatherEvents; // defined below

[
 uuid(ABA21482-DDE2-4cf8-9BF9-D95464AC77C2),
 helpstring("ITemp type library"),
 version(1.0)
]
library LTempLib
{
 importlib ("stdole2.tlb");

 // out going interface ///////////////////////
 [
  object,
  uuid(36EAE5EA-633E-474f-B6F1-5CDE5552487E),
  helpstring("IWeatherEvents"),
  oleautomation
 ]
 interface IWeatherEvents : IUnknown
 {
  [helpstring("IWeatherEvents callback")]
   HRESULT OnWeatherChanged( [in] long nTemperature );
 }

 [
  object,
  uuid(9F0C939C-99E2-4a07-94AC-9D84E25AF8EF),
  helpstring("ITemp"),
  oleautomation,
  pointer_default(unique)
 ]
 interface ITemp : IUnknown
 {
  [propput,helpstring("Set the temp")]
   HRESULT Temperature([in] float t);
  [propget,helpstring("Get the temp")]
   HRESULT Temperature([out,retval] float *t);
  [helpstring("Display temp")]
   HRESULT DisplayCurrentTemperature();
 };

 //////////////////////////////////////////////
 interface ITemp;
 [
  uuid(33FE55E3-C85B-4475-B7B4-0B5196FAB0E7)
 ]
 coclass InsideCOM
 {
  interface ITemp;
  [source] interface IWeatherEvents;
 }
}

Class1.cs
---------
using System;
using System.Windows.Forms;
using System.Runtime.InteropServices;

// Outgoing interface which the sink implements
[InterfaceType(ComInterfaceType.InterfaceIsIDispatch)]
[GuidAttribute("36EAE5EA-633E-474f-B6F1-5CDE5552487E")]
public interface IWeatherEvents
{
 void OnWeatherChanged( int nTemperature );
}

// delegate representing the OnWeatherChanged method
// of the outgoing exposed to COM aware clients.
public delegate void WeatherChangedDelegate( int nTemperature );

// [InterfaceType(ComInterfaceType.InterfaceIsDual)]
//public interface ITemperature
//{
// float Temperature { get; set; }
// void DisplayCurrentTemperature();
//
//}

// this is required to tell typelibrary generation tool REGASM.EXE
// to export the public members of TemperatureComponent into a default
// Class Interface in the generated typelibrary
[
 //ComSourceInterfacesAttribute(typeof(IWeatherEvents)),
 ComSourceInterfaces("IWeatherEvents"),
 GuidAttribute("33FE55E3-C85B-4475-B7B4-0B5196FAB0E7"),
 ProgId("TemperatureComponent.TemperatureComponentInterface")
]

// this tells the type lib generation tools to add this class
// along with all of its methods and properties to the typelib file.
//[ClassInterface(ClassInterfaceType.AutoDual)]
public class TemperatureComponent : LTempLib.ITemp
{
 private float m_fTemperature = 0;
 private Timer _t;

 // define an event associated with the WeatherChangedDelegate
 private event WeatherChangedDelegate OnWeatherChanged;
   
 // Public Constructor
 public TemperatureComponent()
 {
  m_fTemperature = 30.0f;
  _t = new Timer();
  _t.Interval = 1000; // 1 seconds
  _t.Tick += new EventHandler(StateChange);
  _t.Enabled = true;
 }

 private void StateChange(object sender, EventArgs args)
 {
  m_fTemperature++;
  if( null != OnWeatherChanged )
  {
   System.Delegate[] foo = OnWeatherChanged.GetInvocationList(); //
just used to check in debugger that there is one thing to invoke
   Object bar = OnWeatherChanged.Target; // didn't tell me anything
helpful just _ComObject
   OnWeatherChanged( (int)m_fTemperature ); // This call causes the
exception
  }
 }
 
 //WeatherIndications GetWeatherIndications();

 //Public Property Accessors (Defines get/set methods)
 public float Temperature
 {
  get { return m_fTemperature; }
  set { m_fTemperature = value;}
 }/* end Temperature get/set property */

 // Public Method that displays the Current Temperature
 public void DisplayCurrentTemperature()
 {
  String strTemp = String.Format("The current temperature at
Marlinspike is : " +
   "{0:####} degrees fahrenheit", m_fTemperature);
  MessageBox.Show(strTemp,"Today's Temperature");
 }/* end DisplayCurrentTemperature */
 
 // Another public method that returns an enumerated type
 //public WeatherIndications GetWeatherIndications()
 //{
 // if(m_fTemperature > 70)
 // {
 // return WeatherIndications.Sunny;
 // }
 // else
 // {
 // // Let's keep this simple and just return Cloudy
 // return WeatherIndications.Cloudy;
 // }
 //}/* end GetWeatherIndications */

}/* end class Temperature */

Form1.java (VJ++)
----------
import com.ms.wfc.app.*;
import com.ms.wfc.core.*;
import com.ms.wfc.ui.*;
import com.ms.wfc.html.*;
import com.ms.com.*;

import itemp.ITemp;
import itemp.IWeatherEvents;
import itemp.InsideCOM;
       
 
/**
 * This class can take a variable number of parameters on the command
 * line. Program execution begins with the main() method. The class
 * constructor is not invoked unless an object of type 'Form1' is
 * created in the main() method.
 */
public class Form1 extends Form implements itemp.IWeatherEvents
{
 Object o;
 ITemp it;
 private int cookie = -1;

 private IWeatherEvents m_iEventListener = null;

 public Form1()
 {
  System.setOut( com.ms.debug.Debugger.out );
  System.setErr( com.ms.debug.Debugger.out );
  // Required for Visual J++ Form Designer support
  initForm();
  try
  {
  //TemperatureComponent t = new TemperatureComponent();
  com.ms.com._Guid g = new com.ms.com._Guid(
"{33FE55E3-C85B-4475-B7B4-0B5196FAB0E7}" );
  o = com.ms.win32.Ole32.CoCreateInstance(
       g,
       null,
       com.ms.win32.win.CLSCTX_INPROC_SERVER,
       InsideCOM.iid );
  it = (ITemp)o;

  IConnectionPoint cp = null;
  
  IConnectionPointContainer container = (IConnectionPointContainer)o;
  cp = container.FindConnectionPoint( IWeatherEvents.iid );
  //cookie = cp.Advise( (IUnknown)
com.ms.com.ComLib.makeProxyRef(this) );
  cookie = cp.Advise( this ); // didn't seem to matter whether
proxyref or not

  } catch( Exception e )
  {
   e.printStackTrace();
   String s = e.getMessage();
   com.ms.wfc.util.Debug.println( s );
  }

  // TODO: Add any constructor code after initForm call
 }
 public void OnWeatherChanged( int nTemperature )
 {
  // nTemperature;
  MessageBox.show("got change event"); // Never reaches this point
  label1.setText( String.valueOf(nTemperature) );
 }
                
                
 /**
  * Form1 overrides dispose so it can clean up the
  * component list.
  */
 public void dispose()
 {
  super.dispose();
  components.dispose();

  // CUnknown iun = (CUnknown)o;
  // iun.Release();
  IConnectionPoint cp = null;
  IConnectionPointContainer container = (IConnectionPointContainer)o;
  cp = container.FindConnectionPoint( IWeatherEvents.iid );
  cp.Unadvise(cookie);
  
 }

 private void button1_click(Object source, Event e)
 {
  it.setTemperature( (float) 12.3 );
  float x = it.getTemperature();
  it.DisplayCurrentTemperature();
 }

 /**
  * NOTE: The following code is required by the Visual J++ form
  * designer. It can be modified using the form editor. Do not
  * modify it using the code editor.
  */
 Container components = new Container();
 Button button1 = new Button();
 Label label1 = new Label();

 private void initForm()
 {
  this.setText("Form1");
  this.setAutoScaleBaseSize(new Point(5, 13));
  this.setClientSize(new Point(292, 273));

  button1.setLocation(new Point(24, 24));
  button1.setSize(new Point(136, 23));
  button1.setTabIndex(0);
  button1.setText("Help me...");
  button1.addOnClick(new EventHandler(this.button1_click));

  label1.setLocation(new Point(24, 80));
  label1.setSize(new Point(168, 32));
  label1.setTabIndex(1);
  label1.setTabStop(false);
  label1.setText("help m. . . . . ");

  this.setNewControls(new Control[] {
       label1,
       button1});
 }

 /**
  * The main entry point for the application.
  *
  * @param args Array of parameters passed to the application
  * via the command line.
  */
 public static void main(String args[])
 {
  Application.run(new Form1());
 }
}