为什么我的矩形不显示？

Question

我不明白为什么我的矩形没有被显示出来。 我制作了xaml，数据绑定了画布，并正确初始化。 我错过了什么，它只显示一个空白屏幕。 它应该显示数字图8.

MODEL：

namespace Final
{
    class Model : INotifyPropertyChanged
    {
        // define our property chage event handler, part of data binding
        public event PropertyChangedEventHandler PropertyChanged;

        // implements method for data binding to any and all properties
        private void OnPropertyChanged(string propertyName)
        {
            if (PropertyChanged != null)
            {
                PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
            }

        }

        private double _topTopHorizontal;
        public double topTopHorizontal
        {
            get { return _topTopHorizontal; }
            set
            {
                _topTopHorizontal = value;
                OnPropertyChanged("topTopHorizontal");
            }
        }

        private double _leftTopHorizontal;
        public double leftTopHorizontal
        {
            get { return _leftTopHorizontal; }
            set
            {
                _leftTopHorizontal = value;
                OnPropertyChanged("leftTopHorizontal");
            }
        }


        public void initModel()
        {
            topTopHorizontal = 50;
            leftTopHorizontal = 50;
        }








    }
}

主要

    public partial class MainWindow : Window
    {
        private Model model;
        public MainWindow()
        {
            InitializeComponent();


        }

        private void WindowLoaded(object sender, RoutedEventArgs e)
        {
            // create an instance of our Model
            model = new Model();
            model.initModel();



        }






    }
}