C# WinForm 檢測文件是否被佔用

#region 檢測文件狀態及操作方式選擇
[DllImport("kernel32.dll")]
private static extern IntPtr _lopen(string lpPathName, int iReadWrite);
[DllImport("kernel32.dll")]
private static extern bool CloseHandle(IntPtr hObject);
private const int OF_READWRITE = 2;
private const int OF_SHARE_DENY_NONE = 0x40;
private static readonly IntPtr HFILE_ERROR = new IntPtr(-1);
/// <summary>
/// 檢測文件是否只讀或被使用
/// </summary>
/// <param name="FileNames">要檢測的文件</param>
/// <returns>true可用，false在用或只讀</returns>
public static bool CheckFilesState(string fileName)
{
    if (!File.Exists(fileName))
        return true;//文件不存在
    if ((File.GetAttributes(fileName) & FileAttributes.ReadOnly) == FileAttributes.ReadOnly)
        return false;       //文件只讀
    IntPtr vHandle = _lopen(fileName, OF_READWRITE | OF_SHARE_DENY_NONE);
    if (vHandle == HFILE_ERROR)
        return false;       //文件被佔用
    CloseHandle(vHandle);   //文件沒被佔用
    return true;
}
/// <summary>
/// 檢測文件是否只讀或被使用，並由用戶選擇是否繼續操作
/// </summary>
/// <param name="fileFullName">要檢測的文件</param>
/// <returns>true已在用，false未用</returns>
public static bool FileHasOpened(string fileFullName)
{
    bool lOpened = false;
    bool lRetry = true;
    do
    {
        if (!CheckFilesState(fileFullName))
        {
            if (DialogResult.Cancel == MessageBox.Show("文件只讀或已經被打開，請處理後再操作！", "系統錯誤！", MessageBoxButtons.RetryCancel, MessageBoxIcon.Warning))
            {
                lRetry = false;
                lOpened = true;
            }
        }
        else
            lRetry = false;
    } while (lRetry);
    return lOpened;
}
#endregion