Cross-thread GUI call

OK... no.

If you aren't on the GUI thread, you cannot do this. Just because your
user can't do anything doesn't change it; the user is not the only
thing using that thread. In fact, only a slim minority of the events
that a form gets are directly caused by the user.

In 2.0 the implementation will (correctly) catch you doing this and
snigger at you (right before it throws an exception at your background
thread); so you must either use Invoke/BeginInvoke to get back at the
UI thread, else obtain the information you need *first* (before
starting the second thread).

Marc

It is not safe. Use the BackgroundWorker component, which uses BeginInvoke
and EndInvoke to marshal an object to the UI thread, then execute it's
parameters there, usually info to update progress bars, text, etc.

"Jake Weller" <no_spam@_nospam.comwrote in message
news:eZ**************@TK2MSFTNGP05.phx.gbl...

Hi everyone,

Is it safe to call a GUI control's members directly from another thread.
That is, if I launch a background thread when the user clicks a button on
my form, can I safely retrieve info from one of its controls on that
thread. I assume that behind the scenes the call will occur back on the
GUI thread which should be fine since I have a "Work in progress" dialog
running at the time (so its message pump can handle the cross-thread call
accordingly). AFAIK then, synchronization shouldn't be an issue under
these circumstances. Can someone confirm this is safe. Thanks for your
help.

"Chris Bordeman"
<RE*********************************************** ***@hhoottmmaaiill.com>
wrote in message news:eo**************@TK2MSFTNGP04.phx.gbl...

It is not safe. Use the BackgroundWorker component, which uses
BeginInvoke and EndInvoke to marshal an object to the UI thread, then
execute it's parameters there, usually info to update progress bars, text,
etc.

Thanks for the feedback. I already am using the "BackgroundWorker" component
but need to read data from my form on the worker thread. The form itself is
completely off-limits to the user during this time since a "work in
progress" (modal) dialog sits on top of it while my thread runs (as
mentioned earlier). You're saying this still isn't safe though? I've read
the following:

http://msdn2.microsoft.com/en-us/library/ms171728.aspx

and I'm not receiving the "InvalidOperationException" exception they refer
to. Ok, maybe it's potentially dangerous anyway (not sure which is why I'm
here) but given that I'm only reading (not writing) data from a dialog that
can't be altered by the user during this time (only by my worker thread),
you're still saying it's not safe?