在C＃中打开一个空列表

Question

I'm making an app, that use one list's content, to open another list. But to make the app work, it needs to open up a list from IsolatedStorage that contains nothing, the list exists, but it's empty.

In the first MainPage.xaml.cs i create a new list, save the list to IsolatedStorage and then i pass the list's name to the other SecondPage.xaml.cs page:

String listName; //Declared global in class

IsolatedStorageSettings settings = IsolatedStorageSettings.ApplicationSettings;

List<String> emptyList = new List<String>();
settings.Add(listName, emptyList);
settings.Save();

//Here i'm passing it to the second page

NavigationService.Navigate(new Uri("/subjectsPage.xaml?key=" + listName, UriKind.Relative));

Here is the second class that handles this information and tries to open the empty list

IsolatedStorageSettings settings; //Declared global in class

settings = IsolatedStorageSettings.ApplicationSettings; //Executed in public secondPage() method

Helper method:

        private static object readSetting(string key)
    {
        return IsolatedStorageSettings.ApplicationSettings.Contains(key) ? IsolatedStorageSettings.ApplicationSettings[key] : null;
    }

Code to open the list itself, but it fails here, and the exception is called where the "//Failed" line is:

List List; //Declared global in class

protected override void OnNavigatedTo(NavigationEventArgs e)
    {
        if (NavigationContext.QueryString.ContainsKey("key"))
        {
            string listName= NavigationContext.QueryString["key"];
            try
            {
                //Clear listBoxjust in case
                listBox.Clear();

                List = readSetting(listName) != null ? (List<String>)readSetting(listName) : new List<String>();
            }
            catch (Exception)
            {
              //Failed
            }
        }
    }

Do you have any ideas on how to fix this issue? Could i for instance add an empty string to the list, and then remove it after the list is loaded when the other page executes onNavigatedTo()???

Answer 1

I actually found out, that the error was that i tried to clear an un-initialized list like this:

            //Clear listBoxjust in case
            listBox.Clear();