Going through a Pivot control really fast crashes - silverlight

Question

I have a pivot control and a button which does selectedIndex++ and when the selectedIndex has gone passed the last entry it will open up a messagebox asking the user if they want to quiz.
But during testing if you spam the button it will create a 0x8000ffff error when you open the MessageBox.
How do I stop this from happening? is it something to do with the ui thread being too busy or continuing to move the pivot? is the button event still running after I try to navigate out of the page?
this is what the code that does the selectedIndex++
void gotoNextQuestion()
{
if (quizPivot.SelectedIndex < App.settings.currentTest.Questions.Count() - 1)
{
//xScroll -= scrollAmount;
//moveBackground(xScroll);
if (!stoppedPaging)
{
quizPivot.SelectedIndex++;
}
//App.PlaySoundKey("next");
}
else
{
if (App.settings.testMode == App.TestModes.TrainingRecap)
{
MessageBoxResult result;
if (countAnsweredQuestions() == App.settings.currentTest.Questions.Count())
{
stoppedPaging = true;
result = MessageBox.Show("You have reviewed every training question, would you like to go back to the main menu?", "Training Over", MessageBoxButton.OKCancel);
stoppedPaging = false;
if (result == MessageBoxResult.OK)
{
positionableSpriteRadioButton.IsAnswered -= new Action<bool>(Answers_IsAnsweredCompleted);
spriteRadioButton.IsAnswered -= new Action<bool>(Answers_IsAnsweredCompleted);
App.settings.currentTest = null;
NavigationService.Navigate(new Uri("/MainPage.xaml", UriKind.Relative));
return;
}
}
}
else
{
MessageBoxResult result;
if (countAnsweredQuestions() == App.settings.currentTest.Questions.Count())
{
stoppedPaging = true;
result = MessageBox.Show("You have answered all of the questions, are you sure you want to finish?", "Are you sure you want to finish?", MessageBoxButton.OKCancel);
stoppedPaging = false;
}
else
{
checkFinishConditions();
}
}
quizPivot.SelectedIndex = 0;
//App.PlaySoundKey("begin");
}
App.settings.currentTest.currentQuestion = quizPivot.SelectedIndex;
}

Answer 1

Well, one thing is for sure
positionableSpriteRadioButton.IsAnswered -= new Action<bool>(Answers_IsAnsweredCompleted);
That isn't going to work. You're creating a new Action every time. So nothing will have the same reference id, and thus nothing will be removed.
Instead you should remove the Action<bool> and simply subscribe/unsubscribe with
positionableSpriteRadioButton.IsAnswered -= Answers_IsAnsweredCompleted;
And when you subscribe
positionableSpriteRadioButton.IsAnswered += Answers_IsAnsweredCompleted;
That way you can actually remove it again.
But I would recommend you not to use a pivot for this type of "wizard". It's abuse of the control, and going to give a really poor user experience.
Also, just because you navigate to another page, it doesn't mean the code stops running. All code in the same expression is executed, unless you add a return statement after the call to NavigationService.Navigate.
Also, always make sure that Navigation is on the UI thread by wrapping all calls to NavigationService.Navigate in a call to Dispatcher.BeginInvoke.