You could use the PhoneApplicationService class to store information about what page you were on last. For example, use OnNavigatedFrom on Page A:
void OnNavigatedFrom(object sender, Eventargs e)
{
PhoneApplicationService.Current.State["LastPage"] = "PageA";
}
And then check for that on the next page:
void OnNavigatedTo(object sender, Eventargs e)
{
if(PhoneApplicationService.Current.State["LastPage"].ToString() == "PageA")
{
// came from page A
}
else
{
// came from a different page
}
}
Hope this helps!
UPDATE:
One more thing I just saw that might be worth trying is using the NavigationService.BackStack property. I haven't tried this, but it seems like it should work. In your OnNavigatedTo event handler, you should be able to get the last entry from the stack to see your last page. This would be simpler and wouldn't require you to set any properties manually. Example:
protected override void OnNavigatedTo(System.Windows.Navigation.NavigationEventArgs e)
{
base.OnNavigatedTo(e);
var lastPage = NavigationService.BackStack.FirstOrDefault();
}
Found here.