问保存变量wp7

EN

NavigationService.Navigate(new Uri("/PanoramaPage1.xaml?selected=item2", UriKind.Relative));

protected override void OnNavigatedTo(System.Windows.Navigation.NavigationEventArgs e)
    {
        string selected = String.Empty;

        //check to see if the selected parameter was passed.
        if (NavigationContext.QueryString.ContainsKey("selected"))
        {
            //get the selected parameter off the query string from MainPage.
            selected = NavigationContext.QueryString["selected"];
        }

        //did the querystring indicate we should go to item2 instead of item1?
        if (selected == "item2")
        {
            //item2 is the second item, but 0 indexed. 
            myPanorama.DefaultItem = myPanorama.Items[1];
        }
        base.OnNavigatedTo(e);
    }

using System.Collections.Generic;

public static Dictionary<string,object> PageContext = new Dictionary<string,object>;

MyComplexObject obj;
int four = 4;
...

App.PageContext.Add("mycomplexobj",obj);
App.PageContext.Add("four",four);

MyComplexObj obj = App.PageContext["mycomplexobj"] as MyComplexObj;
int four = (int)App.PageContext["four"];

if (App.PageContext.ContainsKey("four"))
int four = (int)App.PageContext["four"];

public interface IPhoneApplicationService : IApplicationService
{
     string Name {get; set;}
     object Deactivating();
     void Activating(object state);
}

public class AuthenticationService : IPhoneApplicationService
{
    public static AuthenticationService Current {get; private set; }

    public void StartService(ApplicationServiceContext context)
    {
        Current = this;
    }

    public void StopService()
    {
        Current = null;
    }

    public string Name {get; set;}

    public object Deactivating()
    {
        // Return an serialisable object such as a Dictionary if necessary.
        return UserID;
    }

    public void Activating(object state)
    {
        UserID = (int)state;
    }

    public int UserID { get; private set; }

    public void Logon(string username, string password)
    {
        // Code here that eventually assigns to UserID.
    }
}

<Application.ApplicationLifetimeObjects>
    <!--Required object that handles lifetime events for the application-->

    <shell:PhoneApplicationService 
        Launching="Application_Launching" Closing="Application_Closing" 
        Activated="Application_Activated" Deactivated="Application_Deactivated"/>

    <local:AuthenticationService Name="AuthServ" />

</Application.ApplicationLifetimeObjects>

    private void Application_Activated(object sender, ActivatedEventArgs e)
    {
        var state = PhoneApplicationService.Current.State;
        foreach (var service in ApplicationLifetimeObjects.OfType<IPhoneApplicationService>())
        {
            if (state.ContainsKey(service.Name))
            {
                service.Activating(state[service.Name]);
            }
        }
    }

    private void Application_Deactivated(object sender, DeactivatedEventArgs e)
    {
        var state = PhoneApplicationService.Current.State;
        foreach (var service in ApplicationLifetimeObjects.OfType<IPhoneApplicationService>())
        {
            if (state.ContainsKey(service.Name))
            {
                state[service.Name] = service.Deactivating();
            }
            else
            {
                state.Add(service.Name, service.Deactivating());
            }
        }
    }

 AuthenticationService.Current.UserID