private void PrintExecute() { try { //we check if user enter valid value for number of coppies if (!ValidationClass.NumberOfCoppiesIsValid(numberOfCopies)) { MessageBox.Show("Morate uneti pozitivan ceo broj manji od 100."); return; } //we check if user enter valid value for number of coppies if (Int32.Parse(numberOfCopies) <= 0 || Int32.Parse(numberOfCopies) >= 100) { MessageBox.Show("Morate uneti pozitivan ceo broj manji od 100."); return; } //if the Background is running we cant call Print commad //program will print a message to user and command will end here if (worker.IsBusy) { MessageBox.Show("Stampanje je vec u toku."); return; } firstPrinting = false; if (!worker.IsBusy) { //this method call DoWork method of Background Worker DoStuff(); } } catch (Exception ex) { MessageBox.Show(ex.ToString()); } }