How to change a Windows Phone start page programmatically?

Question

FYI, I know the title is similar to many posts in this forum, but they don't address this specific problem.
I have the following line in the App.xaml.cs file:
if (!rootFrame.Navigate(typeof(Page1), e.Arguments))
When I change MainPage to Page1, it changes the page you see on startup. So far so good. The problem is:
On Page1 I have checkbox so a user can check "do not show this page again". When a user clicks continue, on the button click event if the box is checked every time the program starts going forward it should load MainPage.
I am working with the following I have found:
To fix this you need to do the following in your tutorial page's button click
// Inside the Button click event of TutorialPage.xaml
// Change the mapping so that MainPage points to itself
((UriMapper)App.RootFrame.UriMapper).UriMappings[0].MappedUri =
new Uri("/MainPage.xaml", UriKind.Relative);
// Since RootFrame.CurrentSource is still set to MainPage, you need to pass
// some dummy query string to force the navigation
App.RootFrame.Navigate(new Uri("/MainPage.xaml?dummy=1", UriKind.Relative));
// Remove back entry so that if user taps the back button
// you won't get back to tutorial
App.RootFrame.RemoveBackEntry();
This seems like what I want, but I get two errors I can't solve.  Error 1 The type or namespace name 'UriMapper' could not be found (are you missing a using directive or an assembly reference?) and Error 2 'My.App' does not
contain a definition for 'RootFrame' 
I can't find a using statement or anything that will remove the URI error. as far as RootFrame, that is used in App.xaml.cs with no errors. It's spelled rootFrame but when I change it in Page1 it doesn't make a difference. I still get the same error. Using
statements are the same for both pages.
I would appreciate any help or a point in the right direction.  I'm using Visual Studio 2013 with the blank Windows Phone template.

Answer 1

I hope I'm not missing something because this is a very obvious solution...
Store a user setting and test it when the app launches.
if(usersetting == true)
if (!rootFrame.Navigate(typeof(Page1), e.Arguments))
else
if (!rootFrame.Navigate(typeof(MainPage), e.Arguments))
That user setting would have to be stored in the local user settings (consider the first line of my code to be pseudo-code).
This works perfectly for a scenario where you have a page that should only launch the first time an app is run or an optional landing page.
I'm a self-taught noob amateur. Please take this into account when responding to my posts or when taking advice from me.