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private void btn1_Click(object sender, EventArgs e)
        {
            if (!backgroundWorker1.IsBusy)
            {
                backgroundWorker1.RunWorkerAsync();
            }
        }

        private void button1_Click(object sender, EventArgs e)
        {
            if (backgroundWorker1.IsBusy)
            {
                backgroundWorker1.CancelAsync();
                 //hier mein code der bei Abbruch ausgeführt werden soll.Wird allerdings nur kurz ausgeführt!!!

             }
        }
 private void backgroundWorker1_DoWork(object sender, DoWorkEventArgs e)
        {
            //for schleife mit 10 durchgängen, die jederzeit abgebrochen werden soll
         }                    

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private void backgroundWorker1_DoWork(object sender, DoWorkEventArgs e)
        {
            int percentFinished = (int)e.Argument;
            while (!backgroundWorker1.CancellationPending && percentFinished < 100) 
            {
                percentFinished++;
                backgroundWorker1.ReportProgress(percentFinished);
                System.Threading.Thread.Sleep(50);
            }
            e.Result = percentFinished; 
        }