C#读写文件的自定义函数，写文件不全的问题的解决方法

/// <summary>
/// winform 读文件 by www.yongfa365.com
/// </summary>
/// <param name="filename">默认读取的文件名</param>
/// <returns></returns>
public string ReadFile(string filename)
{
    ////////////////////////读文件操作////////////////////////
    string html = "";
    OpenFileDialog dlg = new OpenFileDialog();
    dlg.Title = "打开一个文本文件";
    dlg.FileName = filename;
    dlg.Filter = "所有文件(*.*)|*.*|文本文件 (*.txt)|*.txt;*.ini;*.sql";
    if (dlg.ShowDialog() == DialogResult.OK)
    {
        filename = dlg.FileName;
        StreamReader din = new StreamReader(filename, System.Text.Encoding.Default);
        while (din.Peek() > -1)
        {
            html = html + din.ReadToEnd();
        }
        din.Close();
    }
    return html;
}

/// <summary>
/// winform 写文件 by www.yongfa365.com
/// </summary>
/// <param name="filename">文件名</param>
/// <param name="content">文件内容</param>
public void WriteFile(string filename, string content)
{
    SaveFileDialog dlg = new SaveFileDialog();
    dlg.Title = "请选择保存路径";
    dlg.Filter = "所有文件(*.*)|*.*|文本文件 (*.txt)|*.txt;*.ini;*.sql";
    dlg.FileName = filename;
    if (dlg.ShowDialog() == DialogResult.OK)
    {
        filename = dlg.FileName;
        StreamWriter dout = new StreamWriter(filename);
        dout.Write(content);
        //必须写下边这句，关闭当前流，不然输入的文本文件内容不全，只有半截。
        dout.Close();
    }
}