Re: .InvokeRequired always resulting in true

RobKinney1 <RobKinney1@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote:

Here is my confession though... I have 3 seperate browsers in my program.

I presume they are in different windows? With the error below, are your
windows created on different threads? Do you mean to do this?

Contained within ResetAllDataFields(), I destroy and then recreate all of
them (along with resetting a lot of different data). I simply latched onto
myWebBrowser because it was contained withing ResetAllDataFields() and it was
originally the one throwing a COM error when I was calling this from a worker
thread.

I presume you know that you need to do all this work on your GUI thread,
since Windows' windows have thread affinity.

It seemed that in my function, if I just checked this object beforehand, I
would know if ResetAllDataFields needed to be invoked on the main thread..
But technically since I am grabbing all 3 browsers and destroying/creating
them within this function, I could have used any of them right there.

You should create them on the GUI thread, not in your worker thread,
IMO.

Is this sloppy? If so, how can I tell within a function like
ResetAllDataFieldsSafely() whether or not it is being run from a worker
thread or the main thread (without using a random control)?

In your situation, I'd make sure that everywhere that needs to
communicate with the UI has a reference to something which implements
ISynchronizeInvoke (every control does) and pass a delegate to its
Invoke() method.

Because of the way anonymous delegates capture variables from the outer
context, it's as simple as a 'using' block - Invoke + anonymous delegate
simply and relatively efficiently switches context to the GUI and you
can code on.

I put in your suggested code where my original function call was and it
yielded the following error when it came accross another browser object when
destroying and recreating it:

"Controls created on one thread cannot be parented to a control on a
different thread."

That's a pretty serious error. You need to create and parent controls
all on the GUI thread. There are ways to get separate top-level windows
to run on separate threads in WinForms, but it isn't recommended if it
can be avoided, for complexity reasons.

-- Barry

--
http://barrkel.blogspot.com/
.

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