private void RunNavigationJob(NavigationJob nextJob)
{
// We're going to navigate.
IsNavigating = true;
// If the job allows it, checks if the back stack
// already has a page with this Uri. If so, removes
// all back entries before and navigates back to it.
if (nextJob.PreferBackNavigation)
{
// Only navigates back if the back stack contains
// an entry with the same Uri. If so, clears the back
// stack to but not including this entry.
if (this.ClearBackStackFor(nextJob.Uri))
{
// Navigates back to the right page.
RunNavigateBack();
return;
}
// If we're here, no similar entry was found in
// the back stack. So let's fallback to a forward
// navigation.
}
// Back or Forward navigation.
if (nextJob.IsForwardNavigation || nextJob.PreferBackNavigation)
{
RunNavigateForward(nextJob.Uri);
}
else
{
RunNavigateBack();
}
}
private bool CanJobRun(Job nextJob)
{
// Navigation job tests.
if (nextJob is NavigationJob)
{
NavigationJob navJob = (NavigationJob)nextJob;
// Checks if the navigation target is already on screen.
if (navJob.IsForwardNavigation &&
navJob.CancelIfCurrentSource &&
_rootFrame.CurrentSource.OriginalString == navJob.Uri.OriginalString)
{
return(false);
}
// Checks if the navigation initiator is not already on screen.
if (!navJob.IsForwardNavigation &&
navJob.CancelIfNotCurrentSource &&
_rootFrame.CurrentSource.OriginalString != navJob.Uri.OriginalString)
{
return(false);
}
// Checks if the previous page is valid (Back navigation only).
if (!navJob.IsForwardNavigation && !IsPreviousPageValid())
{
return(false);
}
}
// Checks if another navigation was scheduled after this one.
// If so, this job cannot run because the last navigation
// will take over and lead to a back stack conforming.
// (This is because game pages should be left alone on the stack,
// per Wherigo specifications.)
bool isLastJobInQueue;
lock (_syncRoot)
{
isLastJobInQueue = _queue.LastOrDefault() == nextJob;
}
if (!isLastJobInQueue)
{
return(false);
}
// Conditions are good for the job to run.
return(true);
}
