SaveFileDialog在c#中使用streamwriter出现问题

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

public class SaveFileDialogExample
{
    public static void Main()
    {
        SaveFileDialog saveFileDialog = new SaveFileDialog();
        saveFileDialog.Filter = "文本文件|*.txt";
        saveFileDialog.Title = "保存文件";
        saveFileDialog.FileName = "未命名";
        saveFileDialog.DefaultExt = ".txt";

        if (saveFileDialog.ShowDialog() == DialogResult.OK)
        {
            string filePath = saveFileDialog.FileName;
            using (StreamWriter writer = new StreamWriter(filePath))
            {
                writer.WriteLine("这是一个示例文本。");
            }
        }
    }
}