I have a class named as test which triggers an event using the Timer class, the code for which is given below.




The problem that I am facing with, is that the Event runs in a seperate thread and doesn't allow any kind of operation on the Form's controls. The code for the form is given below.

It's a new design change either with VS2005 or with the .NET Framework 2.0 to eliminate alot of concurrency bugs. When the exception handler pops up in VS, click the "more info" link...it will take you to an MSDN article explaining how to properly use delegates to do what you want to do in a thread-safe manner.

Cross Thread Operations
Help Needed @ C#: Cross-thread Operation Not Valid

Yes , you cannot access a windows forms control or a windows forms component from a different thread. What you need to do in order to access the form controls is to invoke the control using a delegate with the help of control.BeginInvoke(). I have posted an article on the issue with sample code on my blog at http://asadsiddiqi.Wordpress.Com/2007/12/24/responsive-user-interfaces-with-ui-threads/
Hope this helps .

Thanks

-reply by Muhammad Asad Siddiqi

I have forgotten how the whole sample did.
Just remember that you have to use
Control.InvokeRequired to check that
if you are not on the right thread.

If so, skill to the next method call and try
to update the control UI.

Wish this help

Eric

Here I am posting the full solution to my own problem. Maybe this will help out some beginners. And no, it didn't take me a year and a half to figure this one out, thanks to MSDN. Its just that I didn't bother to look into this once I had the answer. Anyways, here goes it.

As said by Muhammad, the trick is in using the Control.BeginInvoke (or Control.Invoke) method to force the method to be executed in the same thread as that of the control. The difference between Invoke and BeginInvoke is that the former is synchronous while the latter is asynchronous. Using BeginInvoke makes more sense as the whole idea is to create efficient multi-threaded application. BeginInvoke starts a new thread passing along a delegate object of the method to be invoked and the parameters to be passed to it.

In this case, the BeginInvoke method of the owner Form has to be called from the test class. So, we include an ISynchronizeInvoke parameter in the constructor of the class which is then stored in a member variable. The ISynchronizeInvoke Interface must be implemented in-order to execute a delegate asynchronously. Thankfully, this has been done in the System.Windows.Forms.Control class, so it doesn't require any work on our part.



We add a new delegate with the same signature as that of the method Tick (the event handler for the System.Timers.Timer's elapsed event).



The Tick method makes sure that it is running in the same thread as that of the Synchronizing object passed to the class's constructor using the Control.InvokeRequired property. If it is not, it calls the BeginInvoke method of the SyncObject passing along a delegate to itself and an object array of it's parameters. No further work is done in this call to the Tick method. After a while, the Tick method is invoked again, only this time on the owner form's thread. The InvokeRequired property returns false and the actual work of the method is done.



Only one change needs to be made in the Form class - a reference to itself must be passed to the contstructor of the test class. For this, the instantiation of the object is now done inside the constructor (this keyword is only valid inside a non-static property, method, or constructor).



Full code for the two classes:-

Test class



Form Class



This post has been edited by turbopowerdmaxsteel: Jun 22 2008, 02:34 AM