Xamarin窗体调试错误

<?xml version="1.0" encoding="utf-8" ?>
<ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
             x:Class="MyApp.MainPage">
    <StackLayout>
        <Label Text="{Binding Greeting}" FontSize="24" HorizontalOptions="Center" />
        <Entry Text="{Binding UserInput, Mode=TwoWay}" Placeholder="Enter text here" />
        <Button Text="Submit" Clicked="OnSubmitClicked" />
    </StackLayout>
</ContentPage>

using Xamarin.Forms;

namespace MyApp
{
    public partial class MainPage : ContentPage
    {
        public MainPage()
        {
            InitializeComponent();
            BindingContext = new MainViewModel();
        }

        private void OnSubmitClicked(object sender, EventArgs e)
        {
            // Handle submit logic here
        }
    }

    public class MainViewModel : INotifyPropertyChanged
    {
        private string _greeting = "Hello, Xamarin!";
        private string _userInput;

        public string Greeting
        {
            get { return _greeting; }
            set
            {
                if (_greeting != value)
                {
                    _greeting = value;
                    OnPropertyChanged(nameof(Greeting));
                }
            }
        }

        public string UserInput
        {
            get { return _userInput; }
            set
            {
                if (_userInput != value)
                {
                    _userInput = value;
                    OnPropertyChanged(nameof(UserInput));
                }
            }
        }

        public event PropertyChangedEventHandler PropertyChanged;

        protected virtual void OnPropertyChanged(string propertyName)
        {
            PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
        }
    }
}