Thread problem with control delegate

[jecheney@gmail.com]

Hi,

>From the code below, I have this method/delegate which is called from

another thread, Debug_Console is a listbox control on my main form, i
created the delegate to avoid the cross threading error. Now the
strange thing is, when i call the method from my other thread, the
entry string is added to the listbox, but it also throws an exception
after the string is added. I cant work out why.

The exception is:
=============== ==========
System.InvalidO perationExcepti on: Cross-thread operation not valid:
Control 'DebugConsole' accessed from a thread other than the thread it
was created on.
at System.Windows. Forms.Control.g et_Handle()
at System.Windows. Forms.Control.S endMessage(Int3 2 msg, Int32
wparam, String lparam)
at System.Windows. Forms.ListBox.N ativeAdd(Object item)
at System.Windows. Forms.ListBox.O bjectCollection .AddInternal(Ob ject
item)
at System.Windows. Forms.ListBox.O bjectCollection .Add(Object item)
at UsenetProject.M ainForm.Debug_C onsole_Add_Item (String entry) in C:
\Users\Jack\Doc uments\Misc Stuff\My Programs\Usenet Project
\UsenetProject\ UsenetProject\F orm1.cs:line 46
=============== ==========

I thought the whole point of invoking the new delgate is to avoid the
cross threading problem, what am i doing wrong?

My code:
public delegate void UpdateDebugCons oleDelegate(str ing entry);

public void Debug_Console_A dd_Item(string entry)
{
if (this.DebugCons ole.InvokeRequi red)
{
UpdateDebugCons oleDelegate theDelegate = new
UpdateDebugCons oleDelegate(thi s.Debug_Console _Add_Item);
this.Invoke(the Delegate, new object[] { entry });
}

try
{
DebugConsole.It ems.Add(entry);
}
catch(Exception e)
{
MessageBox.Show (e.ToString());
}
}


Thanks very much for any help,
Jack

[Peter Duniho]

Re: Thread problem with control delegate

On Wed, 04 Apr 2007 15:46:05 -0700, <jecheney@gmail .comwrote:

[...]
I thought the whole point of invoking the new delgate is to avoid the
cross threading problem, what am i doing wrong?

Looks to me like you left out an "else". :)

Your method should only do the real work in the
!this.DebugCons ole.InvokeRequi red case. Put the whole try/catch block
where you do the real work in the else clause of your if statement and
everything should be fine.

Pete

[jecheney@gmail.com]

Re: Thread problem with control delegate

On 4 Apr, 23:46, jeche...@gmail. com wrote:

Hi,
>

From the code below, I have this method/delegate which is called from

>
another thread, Debug_Console is a listbox control on my main form, i
created the delegate to avoid the cross threading error. Now the
strange thing is, when i call the method from my other thread, the
entry string is added to the listbox, but it also throws an exception
after the string is added. I cant work out why.
>
The exception is:
=============== ==========
System.InvalidO perationExcepti on: Cross-thread operation not valid:
Control 'DebugConsole' accessed from a thread other than the thread it
was created on.
at System.Windows. Forms.Control.g et_Handle()
at System.Windows. Forms.Control.S endMessage(Int3 2 msg, Int32
wparam, String lparam)
at System.Windows. Forms.ListBox.N ativeAdd(Object item)
at System.Windows. Forms.ListBox.O bjectCollection .AddInternal(Ob ject
item)
at System.Windows. Forms.ListBox.O bjectCollection .Add(Object item)
at UsenetProject.M ainForm.Debug_C onsole_Add_Item (String entry) in C:
\Users\Jack\Doc uments\Misc Stuff\My Programs\Usenet Project
\UsenetProject\ UsenetProject\F orm1.cs:line 46
=============== ==========
>
I thought the whole point of invoking the new delgate is to avoid the
cross threading problem, what am i doing wrong?
>
My code:
public delegate void UpdateDebugCons oleDelegate(str ing entry);
>
public void Debug_Console_A dd_Item(string entry)
{
if (this.DebugCons ole.InvokeRequi red)
{
UpdateDebugCons oleDelegate theDelegate = new
UpdateDebugCons oleDelegate(thi s.Debug_Console _Add_Item);
this.Invoke(the Delegate, new object[] { entry });
}
>
try
{
DebugConsole.It ems.Add(entry);
}
catch(Exception e)
{
MessageBox.Show (e.ToString());
}
}
>
Thanks very much for any help,
Jack

Brilliant thanks very much, that fixed it.

[jecheney@gmail.com]

Re: Thread problem with control delegate

Given the above (working) code, i now have the problem that if i close
the main form/program while the new thread is working, I get an
exception that it cannot access a disposed object.

what's the best way to avoid this problem? i.e stopping the thread
before the main form object is disposed.

[gshzheng]

Re: Thread problem with control delegate

this.DebugConso le.InvokeRequir ed

should be

this.InvokeRequ ired

<jecheney@gmail .com>
??????:11757290 42.134981.26625 0@n76g2000hsh.g ooglegroups.com ...

Given the above (working) code, i now have the problem that if i close
the main form/program while the new thread is working, I get an
exception that it cannot access a disposed object.
>
what's the best way to avoid this problem? i.e stopping the thread
before the main form object is disposed.
>
>
>
>
>

[Peter Duniho]

Re: Thread problem with control delegate

On Wed, 04 Apr 2007 16:24:02 -0700, <jecheney@gmail .comwrote:

Given the above (working) code, i now have the problem that if i close
the main form/program while the new thread is working, I get an
exception that it cannot access a disposed object.
>
what's the best way to avoid this problem? i.e stopping the thread
before the main form object is disposed.

Hard to say for sure. It depends on what exactly your form and your
thread do and are doing when the form is closed. However, the two usual
approaches would be to either alert the thread to stop processing and exit
before you close the form, or to have the thread check to see if the form
is still around before trying to use it (in the invoking method, for
example).

Pete