Best way to show a passcode screen everytime an app is launched/activated - windows-phone-8

Question

I am working on a Windows Phone 8 App which should be protected with a passcode. What is the best way to show the passcode screen everytime the app is lauchend or activated?
I think the central point of action shoule be the App.xaml.cs with its Launch and Activation event handlers. But how exactly can I show the passcode screen?
The problem is, that one never know which pages will be displayed when the app launches or is reactivated. It is either the main page or any other page which was last displayed when the app was deactivated.
I tried to intercept the navigation to the first page, cancel it and show the passcode page instead:
// App.xaml.cs
private void InitializePhoneApplication() {
...
RootFrame.Navigating += HandleFirstNavigation;
...
}
private void HandleFirstNavigation(object sender, NavigatingCancelEventArgs e) {
RootFrame.Navigating -= HandleFirstNavigation;
e.Cancel = true;
RootFrame.Dispatcher.BeginInvoke(new Action(this.OpenPasscodePage));
}
private void OpenPasscodePage() {
RootFrame.Navigate(PasscodePageUri);
}
This works, but only when the app lauchend. When the app reactivated (dormant or tombstoned) the e.Cancel is irgnored. Although the navigation to the passcode page is called the original page is shown.
Moving the navigation the the passcode page from Navigating to Navigated does not worth either:
private void InitializePhoneApplication() {
...
RootFrame.Navigated += PasscodePageAfterFirstNavigation;
...
}
private void PasscodePageAfterFirstNavigation(object sender, EventArgs e) {
RootFrame.Navigated-= PasscodePageAfterFirstNavigation;
RootFrame.Navigate(PasscodePageUri);
}
This seems to be some kind of race condition: Sometimes the passcode page is shown, sometimes the original page. Even if the passcode pages comes up this looks bad because one first see the original page for the fraction of a second before the app navigates further to the passcode page.
Both solution do not work. Any idea what is the right way to implement this?
EDIT: Meanwhile I tried a third solution which does not work either. This solution uses the Uri Mapper:
App.xaml.cs
public bool PasscodeWasConfirmed; private void Application_Launching(object sender, LaunchingEventArgs e) {
...
PasscodeWasConfirmed = false;
...
}
private void Application_Activated(object sender, ActivatedEventArgs e) {
...
PasscodeWasConfirmed = false;
...
}
public Uri InitialPageUri;
public bool ShouldRedirectToPasscodePage(Uri uri) {
if (PasswordWasConfirmend == false) {
InitialPageUri = uri;
return true;
}
return false;
}
UriMapper
public class AppUriMapper : UriMapperBase {
public override Uri MapUri(Uri uri) {
App app = (Application.Current as App);
if (app != null) {
if (app.ShouldRedirectToPasscodePage(uri))
return PasscodeQueryPage.PageUri;
}
// default
return uri;
}
}
PasscodePage
public partial class PasscodePage : PhoneApplicationPage {
...
private void PasscodeConfirmed() {
App app = (Application.Current as App);
app.PasscodeWasConfirmed = true;
NavigationService.Navigate(app.InitialPageUri);
}
}
The Logic is working without any problem, but the app does not navigate to InitialPageUri after the passcode was confirmed. The Uri Mapper is called and correctly and returns the InitialPageUri (no redirect any more). But no navigation happens...
There are no errors, exceptions or debug output. simply nothing happes...
Biggest problem when using Uri Mapper:
When the app is reactivated from Dormant state there is no navigation which could be mapped or redirected...

Answer 1

(I've edited previous answer instead of adding a new one)
I've spend a little time trying to find a solution, and I don't see why your code doesn't run.
In my case it's enough if I do such a change in App.xaml:
private void CompleteInitializePhoneApplication(object sender, NavigationEventArgs e)
{
// Set the root visual to allow the application to render
if (RootVisual != RootFrame)
RootVisual = RootFrame;
// Remove this handler since it is no longer needed
RootFrame.Navigated -= CompleteInitializePhoneApplication;
App.RootFrame.Navigate(new Uri("/passPage.xaml", UriKind.RelativeOrAbsolute));
}
This works on my example which is under the link http://sdrv.ms/1ajH40E
But - I cannot prevent user from seeing last screen when he holds back buton and is chosing to which app return, and then for a blink he can see the last page before leaving the app. I don't know if it is possible to change this behaviour after clicking MS Button:
windows phone change deactivated app image
Second edit
Ok - maybe I've found solution why it sometiems work and sometimes not in your code. After pressing the Start or Search buton the App can go to two cases: Tombstone and non-tombsone. After return different events happen. Code above works with Tombstone case but not with non-tombstone. To work it with the second you need to add (because page is not initialized again) - (of course it can be different solution):
bool afterActivation = false;
private void Application_Activated(object sender, ActivatedEventArgs e)
{
afterActivation = true;
}
private void CheckForResetNavigation(object sender, NavigationEventArgs e)
{
// If the app has received a 'reset' navigation, then we need to check
// on the next navigation to see if the page stack should be reset
if (e.NavigationMode == NavigationMode.Reset)
RootFrame.Navigated += ClearBackStackAfterReset;
if (afterActivation)
{
afterActivation = false;
App.RootFrame.Navigate(new Uri("/passPage.xaml", UriKind.RelativeOrAbsolute));
}
}
Please also ensure of your debug properties in VS: Project->Properties->Debug->Tombstone upon deactiovation checkbox.
You can also find some information here (if you haven't seen it before):
http://blogs.msdn.com/b/ptorr/archive/2010/12/11/how-to-correctly-handle-application-deactivation-and-reactivation.aspx