C#

string sourceFile, destinationFile;

       private void ShowLoadingIcon()
       {
           if (InvokeRequired)
           {
               this.Invoke(new MethodInvoker(ShowLoadingIcon));

           }
           else
           {
               pixLoadingIcon.Visible = true;
           }
       }



       private void btnConvert_Click(object sender, EventArgs e)
       {
           ShowLoadingIcon();

           //start thread to process long running task
           System.Threading.Thread t = new System.Threading.Thread(() =>
           {
               ConvertFiles(sourceFile, destinationFile);
           });

           t.Start();

       }


       private void ConvertFiles(string src, string dest)
       {
           //long running task to convert files
       }