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Asked: 2026-05-21T02:28:15+00:00

I have a .NET remoting client activated object type client-server application. I’m using Visual

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I have a .NET remoting client activated object type client-server application. I’m using Visual Studio 2010 targeting the .NET Framework 4. When I run without debugging, the program works fine – the clients can connect no problem. But when I try to debug, on the line in the client code where I have the ‘new’ operator, the server (I think) throws an exception.

What I want to do is keep references to the remote objects created in the server code. So in my Remote Object’s constructor I have this line: 

Cache.GetInstance().addFireFighter(this);

When I debug, this code runs fine too. But when it goes back to the remote object’s line to call the addFireFighter method, that’s when it crashes. Here’s the addFireFighter method:

public static IServer _server;

public void addFireFighter(FireFighter ff)
{
    _server.addFireFighter(ff);
}

And the _server.addFireFighter method:

public void addFireFighter(FireFighterResponder.FireFighter ff)
{
    _ffList.Add(ff); // -> works fine :S
    Console.WriteLine("FireFighterResponder addFireFighter added");
    lstBox.Items.Add(ff); //-> CRASH!!
}

Observation: When I run the server without debugging but run the client in debug mode, it still works fine.

This is a school project and I’m new to C# .NET remoting. I implemented the same in Java and had no issue. So I can give my whole project if somebody wants to look at it. Maybe I have a design flaw.

Here’s the stack trace:

System.Reflection.TargetInvocationException: Exception has been thrown by the target of an invocation. ---> System.InvalidOperationException: Cross-thread operation not valid: Control 'lstBox' accessed from a thread other than the thread it was created on.
   at System.Windows.Forms.Control.get_Handle()
   at System.Windows.Forms.ListBox.NativeAdd(Object item)
   at System.Windows.Forms.ListBox.ObjectCollection.AddInternal(Object item)
   at System.Windows.Forms.ListBox.ObjectCollection.Add(Object item)
   at FirefighterMonitorSystem.BaseStation.addFireFighter(FireFighter ff) in C:\Users\Dula\Documents\My Dropbox\Firefighter\453\FirefighterMonitorSystem\FirefighterMonitorSystem\BaseStation.cs:line 35
   at FireFighterResponder.Cache.addFireFighter(FireFighter ff) in C:\Users\Dula\Documents\My Dropbox\Firefighter\453\FirefighterMonitorSystem\FireFighterResponder\Cache.cs:line 33
   at FireFighterResponder.FireFighter..ctor() in C:\Users\Dula\Documents\My Dropbox\Firefighter\453\FirefighterMonitorSystem\FireFighterResponder\FireFighter.cs:line 20
   --- End of inner exception stack trace ---

The lstBox is a .NET ListBox in my server code where I add each Remote object. But what still confuses me is why it works when not in debug mode.

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1 Answer

  1. Editorial Team

    You have to look at the exception’s InnerException property to know what went really wrong.

    You are accessing a control from a thread other than the main thread (aka UI thread). This is illegal, windows are not thread-safe. You must use Control.Begin/Invoke(). You don’t get the exception without the debugger because this thread checking is only enabled by default when a debugger is attached. That doesn’t mean it is safe to run code without a debugger, it will randomly cause paint problems or deadlock, although you may have to wait a day or a week for that to happen.

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