Question

I am building an app for Windows Phone 7.1 using c#.

when the app is opening, if the user is the first time using it, then go to the “set up a password” page, else go to the “login page”.

I wanted to use NavigationService.Navigate(Uri), but I don’t know where should i call this function?

Answer 1

I suggest to save the password to some sort of (encrypted) persistent storage, and try to retrieve it when the app starts.

Then add this code in the App.xaml and it should do the trick

void RootFrame_Navigating(object sender, NavigatingCancelEventArgs e)
{
    // Only care about MainPage 
    if (e.Uri.ToString().Contains("/MainPage.xaml") != true) 
         return;

    var password = GetPasswordFromSomePersistentStorage();

    // Cancel current navigation and schedule the real navigation for the next tick 
    // (we can't navigate immediately as that will fail; no overlapping navigations 
    // are allowed) 
    e.Cancel = true; 
    RootFrame.Dispatcher.BeginInvoke(delegate 
    { 
        if (string.IsNullOrWhiteSpace(password)) 
            RootFrame.Navigate(new Uri("/InputPassword.xaml", UriKind.Relative)); 
        else 
            RootFrame.Navigate(new Uri("/ApplicationHome.xaml", UriKind.Relative)); 
    });
}

Make sure you have added the handler on the App() constructor

RootFrame.Navigating += new NavigatingCancelEventHandler(RootFrame_Navigating);

And also, the MainPage.xaml, is just and empty page (set it up as you begin page) that will be used to catch the initial navigation event.

Hope its helps.