Tombstoning a List on Windows Phone 8

Question

I am trying to save the state of a listbox on wp. I used this this method to tombstone the content of a textbox and it worked perfectly but I am having problems for a list of strings :

Basically I have a list of strings called beta and I have to click on a button to generate the list. So I would like that if I close or deactivate my application and then relaunch it, the list shows up without pressing the button

   List<string> beta;

   private void b_Click_1(object sender, RoutedEventArgs e)
   {
            List<string> beta = new List<string>{
                "string","string","string",
                "string","string","string",
                "string", };

            list.ItemsSource = beta;
            phoneAppService.State["_List"] = beta;
   }

   private void PhoneApplicationPage_Loaded_1(object sender, RoutedEventArgs e)
   {
            object myValue;

            if(phoneAppService.State.TryGetValue("_List", out List<myValue)> ){
                 list.ItemsSource  = myValue;
            }
   }

but a problem occurs at :

phoneAppService.State.TryGetValue("MyValue", out List<myValue)>

Although this method works with one string it does not with a list.

Which method should I use for a list of strings?

EDIT :

Here are my methods in my app.xaml.cs class that I call when the app is closed, deactivated, launched or opened :

 private void SaveState() {
            PhoneApplicationService phoneAppService = PhoneApplicationService.Current;

            IsolatedStorageSettings settings = IsolatedStorageSettings.ApplicationSettings;

            settings["MyValue"] = phoneAppService.State["MyValue"];

            if(settings.Contains("_List")){
                settings["_List"] = phoneAppService.State["_List"];
            }
        }

        private void LoadState() {
            PhoneApplicationService phoneAppService = PhoneApplicationService.Current;

            IsolatedStorageSettings settings = IsolatedStorageSettings.ApplicationSettings;

            string myValue = "";
            if(settings.TryGetValue<string>("MyValue", out myValue  )){

                phoneAppService.State["MyValue"] = myValue;
            }

           List<string> myValues;
            if (settings.TryGetValue<List<string>>("_List", out myValues))
            {
                phoneAppService.State["_List"] = myValues as List<string>;
            }
        }

As I said earlier this method works for a string which is properly restored in a textbox but not for a list of string

Answer 1

It appears that beta is already a List<string> when you add it to State. When you pull it out, it should already be a List<string>, so you don't need to turn it into a List<myvalue> in the TryGetValue call. It should look something much more straightforward, like:

private void PhoneApplicationPage_Loaded_1(object sender, RoutedEventArgs e)
{
    object myValue;
    if(phoneAppService.State.TryGetValue("_List", out myValue))
    {
        list.ItemsSource  = myValue as List<string>;
    }
}