using WinAPI functions in C#

If the process is so long that it holds up your program between calls to Application.DoEvents(), then you should probably put it in a thread. When a working process is in its own thread, the main window will always respond to events in a timely manner.

Thanks for your interest first but I tried it and it didn't work.At last I did it by using another table with a status field.Program looks for the value of the status field in that table before the processing of every file .I know it is not efficient but it helps me.

I think that it should respond to the button's click. I think what you're looking for is the Application.DoEvents() method, which calls the program's message loop to process messages such as a WM_LBTNCLICK and such. Stick it in any loop that may run for more than a few hundred milliseconds. That would cause the button click to take effect, and your thread will then be able to cancel the operation. Does that help?

Sorry,I couldn't explain the problem properly.My program reads the files from a local table and controls the each row one by one and then transfers the file to the real database if any problem doesn't exist.During this process I show the progress of each file with a progress bar.And I want to stop this process when I click the button.Program should end the process of the file which has already been read but shouldn't read any more files from the local table. My problem is that system doesn't accept the button's click.I have already done what you advise me but it didn't work.

Why do you need to intercept messages sent by this button? You can just set a boolean value in the onclick event of the button that will tell the thread that it is time to terminate. Consider this... private static isaborted = false; private void cmdstart_Click(object sender, System.EventArgs e) { ThreadStart mythreadstart = new ThreadStart(threadproc); Thread mythread = new Thread( mythreadstart ); isaborted = false; mythread.Start(); } private void cmdstop_Click(object sender, System.EventArgs e) { isaborted = true; } private threadproc() { while (!isaborted) { /* dostuff */ } }