我想在文本框中显示textfile中的文本.我怎么能这样做..在C#中

using System;
using System.IO;
using System.Windows.Forms;

public class Form1 : Form
{
    private TextBox textBox1;

    public Form1()
    {
        textBox1 = new TextBox();
        textBox1.Multiline = true;
        textBox1.Dock = DockStyle.Fill;
        Controls.Add(textBox1);
    }

    public void ShowTextFile(string filePath)
    {
        if (File.Exists(filePath))
        {
            try
            {
                string text = File.ReadAllText(filePath);
                textBox1.Text = text;
            }
            catch (Exception ex)
            {
                MessageBox.Show("Error: Could not read file. Original error: " + ex.Message);
            }
        }
        else
        {
            MessageBox.Show("Error: File not found.");
        }
    }

    [STAThread]
    static void Main()
    {
        Application.EnableVisualStyles();
        Application.SetCompatibleTextRenderingDefault(false);
        Application.Run(new Form1());
    }
}

Form1 form = new Form1();
form.ShowTextFile("textfile.txt");
Application.Run(form);