建一个WPF文件，给出txt文档的路径，将其显示在textbox中

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Imaging;
using System.Windows.Navigation;
using System.Windows.Shapes;
using Microsoft.Win32;
using System.IO;
namespace Cambridge
{
    /// <summary>
    /// MainWindow.xaml 的交互逻辑
    /// </summary>
    public partial class MainWindow : Window
    {
        private OpenFileDialog openFileDialog = null;
        public MainWindow()
        {
            InitializeComponent();
            openFileDialog = new OpenFileDialog();
            openFileDialog.FileOk += openFileDialogFileOk;
        }
        private void Quit_Click(object sender, RoutedEventArgs e)
        {
            this.Close();
        }
        private void openFile_Click(object sender, RoutedEventArgs e)
        {
            openFileDialog.ShowDialog();
        }
        private void openFileDialogFileOk(object sender, System.ComponentModel.CancelEventArgs e)
        {
            string fullPathname = openFileDialog.FileName;
            FileInfo src = new FileInfo(fullPathname);
            filename.Text = src.Name;
            source.Text = "";
            TextReader reader = src.OpenText();
            string line = reader.ReadLine();
            while (line != null)
            {
                source.Text += line + '\n';
                line = reader.ReadLine();
            }
            reader.Close();
        }
    }
}