c#, wpf, tab control change

Question

if some function is running, when u want to change other tabs it should not happen, i need to give pop up like "please stop test and change tab"... how to do this 

 

i trid this code but it is continuosly looping and giving pop up 

 

private async  void TabControl_SelectionChanged(object sender, SelectionChangedEventArgs e)

{

  if (e.OriginalSource == MainTabControl)

    {

        if (MainTabControl.SelectedIndex != -1)

          {

             if (SharedInfo.TestInProgress)

                {

                   //e.Handled = true;

                   if (MainTabControl.SelectedIndex != 0)

                       {

                          MainTabControl.SelectedIndex = 0;

                     

                             await this.ShowMessageAsync(

                             "Test is in Progress...",

                             "Let the test be completed...");

                          return;

                       }

               }

         }

     }

}