How to cancel with button?

Question

Hi I have written a c# windowsapplication to convert an ASCII file. First I select an input file-->with a button a method() reads and converts the content of the file (with for loops) and writes the new content to a new file. How can I cancel this method() with a button? When the methods() runs I can't escape it or use the exit button of the form Greetzzz G

Sam Hobbs · Answer

If you are closing in a thread different from the thread that opens the file then that might be the problem.

Zoran Horvat · Answer

How does the code which reports that file is in use look like? I suppose that you've tried to delete the file before fileout.Close() was executed since Close method should be synchronous i.e. does not exit before file handle has been released.

Gerben Schmidt · Answer

Thanx It works now! I use the async thread. I also want to delete the written files that were cancelled However when I break my loop that writes with the if CancellationPending the last file is still open. how can I close this file? I tried to close the files in this if statement that is breaking my for loop But then the form hangs.... if (bw_Async.CancellationPending) { // Pause for bit to demonstrate that there is time between // Cancelling... and Canceled. Thread.Sleep(1200); //Close file that is cancelled fileout.Close(); // Set the e.Cancel flag so that the WorkerCompleted event // knows that the process was canceled. e.Cancel = true; return; } Someone got an idea?

Sam Hobbs · Answer

Yes there is nothing you can do in the form while the other processing (the processing of the text from the file) is executing if they are all in the same thread. So you need to do as Zoran says; do the other processing in anoher thread. You can do that using the BackgroundWorker class; search this web site's articles and previous answers in the forums for help with the BackgroundWorker class.

Zoran Horvat · Answer

These are general guidelines how to create a stoppable operation: 1. Run operation on a separate thread. This leaves main application thread responsive and ready to process button click and other GUI events. 2. Provide manual reset event to the function which performs operation (initially not set). Owner will set this event when operation should be stopped. 3. Implement button click event handler and in that handler set the event. Then invoke Join method on the thread object which performs operation. This will wait for the thread to terminate. 4. Thread procedure which performs operation must check the event very often e.g. once in every iteration. This is done using WaitOne method with timeout set to zero - in this case method will exit immediately returning true if event is set i.e. thread should quit operation and terminate. 5. When terminating the operation do not forget to cleanup unfinished work. For instance you may want to delete incomplete file.