如何关闭已经打开的txt文本

using using System.Runtime.InteropServices;

[DllImport("kernel32.dll")]
public static extern IntPtr _lopen(string lpPathName, int iReadWrite);

[DllImport("kernel32.dll")]
public static extern bool CloseHandle(IntPtr hObject);

public const int OF_READWRITE = 2;
public const int OF_SHARE_DENY_NONE = 0x40;
public readonly IntPtr HFILE_ERROR = new IntPtr(-1);
private void button1_Click(object sender, EventArgs e)
{
    string vFileName = @"c:\temp\temp.bmp";
    if (!File.Exists(vFileName))
    {
        return;
    }
    IntPtr vHandle = _lopen(vFileName, OF_READWRITE | OF_SHARE_DENY_NONE);
    if (vHandle == HFILE_ERROR)
    {
        //文件被占用
          using (Process p = new Process())
             {
                 p.StartInfo = new ProcessStartInfo("C:\\a.txt");
                 p.Start();
                 p.WaitForExit();
             }
    }
   
    CloseHandle(vHandle);
}