[UWP]コードからバインディングを設定してLocalSettingsの読み書きを行う

trick1___MainPage.xaml

    <Grid>
        <StackPanel Width="400" Margin="50">
            <!--First name-->
            <TextBlock Text="First name:" />
            <TextBox Text="{x:Bind ViewModel.FirstName, Mode=TwoWay}"/>

            <!--Last name-->
            <TextBlock Text="Last name:"  />
            <TextBox Text="{x:Bind ViewModel.LastName, Mode=TwoWay}" />

            <!--Age-->
            <TextBlock Text="Age:" />
            <TextBox Text="{x:Bind ViewModel.Age, Mode=TwoWay}" />
            
        </StackPanel>
    </Grid>

trick1___MainPage.xaml.cs

    public sealed partial class MainPage : Page
    {

        public PersonViewModel ViewModel { get; set; } = new PersonViewModel();

        public MainPage()
        {
            this.InitializeComponent();
        }

    }

trick1___PersonViewModel.cs

    public class PersonViewModel
    {

        private string _FirstName;
        private string _LastName;
        private int _Age;

        //個別に更新

        public string FirstName {
            get { return _FirstName; }
            set { _FirstName = value;
                localSettings.Values[firstNameKey] = FirstName;
            }
        }
        public string LastName
        {
            get { return _LastName; }
            set { _LastName = value;
                localSettings.Values[lastNameKey] = _LastName;
            }
        }
        public int Age
        {
            get { return _Age; }
            set { _Age = value;
                localSettings.Values[ageKey] = _Age;
            }
        }

        // The rest of the class definition
        private ApplicationDataContainer localSettings =
                ApplicationData.Current.LocalSettings;

        private string firstNameKey = nameof(FirstName);
        private string lastNameKey = nameof(LastName);
        private string ageKey = nameof(Age);

        /// <summary>
        /// 全部Write　　
        /// </summary>
        public void StoreInSettings()
        {
            localSettings.Values[firstNameKey] = FirstName;
            localSettings.Values[lastNameKey] = LastName;
            localSettings.Values[ageKey] = Age;

        }
        /// <summary>
        /// ctor
        /// </summary>
        public PersonViewModel()
        {
            if (IsPersonDataStoredInSettings())
            {
                FirstName = localSettings.Values[firstNameKey]?.ToString();
                LastName = localSettings.Values[lastNameKey]?.ToString();
                Age = (int)localSettings.Values[ageKey];
            }
        }
        /// <summary>
        /// データの存在確認
        /// </summary>
        /// <returns>1つでも見つからなかったらFalse</returns>
        private bool IsPersonDataStoredInSettings()
        {
            string[] keys = { firstNameKey, lastNameKey, ageKey };

            var isPersonDataStoredInSettings = true;

            foreach (var key in keys)
            {
                if (!localSettings.Values.ContainsKey(key))
                {
                    isPersonDataStoredInSettings = false;
                    break;
                }
            }

            return isPersonDataStoredInSettings;
        }
    }