Xamarin新的可绑定选择器控件

Question

https://blog.xamarin.com/new-bindable-picker-control-for-xamarin-forms/

我对Xamarin和C＃还是很陌生，不知怎么对我不起作用...

 public class RegistrationPageViewModel : INotifyPropertyChanged
    {

        List<string> _countries = new List<string>
{
    "Afghanistan",
    "Albania",
    "Algeria",
    "Andorra",
    "Angola",

};
        public List<string> Countries => _countries;

        public event PropertyChangedEventHandler PropertyChanged;




    }
    public partial class RegistrationPage : ContentPage
    {
        RegistrationPageViewModel vm;

        public RegistrationPage()
        {
            InitializeComponent();
            this.BindingContext = vm = new RegistrationPageViewModel();
        }

        private void InitializeComponent()
        {
            throw new NotImplementedException();
        }
    }



    int countriesSelectedIndex;
            public int CountriesSelectedIndex
            {
                get
                {
                    return countriesSelectedIndex;
                }
                set
                {
                    if (countriesSelectedIndex != value)
                    {
                        countriesSelectedIndex = value;

                        // trigger some action to take such as updating other labels or fields
                        OnPropertyChanged(nameof(CountriesSelectedIndex));
                        SelectedCountry = Countries[countriesSelectedIndex];
                    }
                }
            }

        public string SelectedCountry { get; private set; }
    }

我收到一个错误：名称“国家”在当前上下文中不存在

我在做什么错？ 有人有可行的例子吗

Answer 1

这是我的写法（使用Fody而不是INotifyPropertyChanged ）：

public class Country
    {
        public string Name { get; }
        public Country(string name) => Name = name;
        public static Country Afghanistan = new Country("Afghanistan");
        public static Country Albania = new Country("Albania");
        public static Country Algeria = new Country("Algeria");
        public static Country Andorra = new Country("Andorra");
        public static Country Angola = new Country("Angola");

        public static IList<Country> Countries = new List<Country> { Afghanistan, Albania, Algeria, Andorra, Andorra, Angola };
    }

    [ImplementPropertyChanged]
    public class RegistrationPageViewModel
    {
        public Country SelectedCountry { get; set; }
    }

    public class RegistrationPage : ContentPage
    {
        public RegistrationPage()
        {
            var vm = new RegistrationPageViewModel();
            BindingContext = vm;
            var picker = new Picker();
            foreach (var country in Country.Countries) picker.Items.Add(country.Name);
            picker.SetBinding<RegistrationPageViewModel>(Picker.SelectedIndexProperty, x => x.SelectedCountry, converter: new PickerItemsToTypeConverter<Country>(Country.Countries));
            Content = picker;
        }
    }

    public class PickerItemsToTypeConverter<T> : IValueConverter
    {
        private readonly IList<T> _pickerItemsList;

        public PickerItemsToTypeConverter(IList<T> pickerItemsList) => _pickerItemsList = pickerItemsList;

        public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
        {
            var itemType = (T)value;
            return _pickerItemsList.IndexOf(itemType);
        }

        public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
        {
            var selectedIndex = value as int?;
            if (selectedIndex == null) throw new Exception("No selection");
            return _pickerItemsList[selectedIndex.Value];
        }
    }