C# _lopen判断文件是否正在被使用

     今天很无语，要解决一个问题，Silverlight中无法对用户打开的文件进行判断，是否打开，沙箱模式运作，出于安全性考虑，是无法获得

本地文件的绝对路径，无法调用API来判断实现这功能，最后还是用Trycatch来解决。

     C#能够调用的API都能从以下网站查到：

          API查询网站：http://www.webtropy.com/articles/Win32-API-DllImport-art9.asp

      还是写下C# 调用系统API来实现文件判断效果:

         1.命名空间：using System.Runtime.InteropServices

         2.  API函数 _lopen(string pathfile,int ireadwriter)

/// <summary>
/// Description of UseAPI.
/// </summary>
    public class UseAPI
    {
        
        public UseAPI()
        {
        }
        
        private const int OF_READWRITE = 2;
        private const int OF_SHARE_DENY_NONE = 0x40;
        private static readonly IntPtr HFILE_ERROR = new IntPtr(-1);

        
        /// <summary>
/// 判断文件是否打开
/// </summary>
/// <param name="lpPathName">文件名称</param>
/// <param name="iReadWrite"></param>
/// <returns></returns>
        [DllImport("kernel32.dll")]
        private static extern IntPtr _lopen(string lpPathName, int iReadWrite);

        /// <summary>
/// 关闭文件句柄
/// </summary>
/// <param name="hObject"></param>
/// <returns></returns>
        [DllImport("kernel32.dll")]
        private static extern bool CloseHandle(IntPtr hObject);
        
        /// <summary>
/// 文件名称
/// </summary>
/// <param name="filename"></param>
/// <returns></returns>
        public static string IsOpen(string filename)
        {
            IntPtr vHandle = _lopen(filename, OF_READWRITE | OF_SHARE_DENY_NONE);
            if (vHandle == HFILE_ERROR)
            {
                CloseHandle(vHandle);
                return "文件被占用！";
            }
            else
                return "没有被占用！";
            
            //CloseHandle(vHandle);
        }
    }