OpenFileDialog过滤文件

   OpenFileDialog ofd = new OpenFileDialog();

   ofd.InitialDirectory = System.Windows.Forms.Application.StartupPath ;
// ofd.Filter = "Microsoft Excel files (*.xls)|*.xls|CSV files (*.csv)|*.csv|All files (*.*)|*.*" ;
   ofd.Filter = "Microsoft Excel files (*.xls;*.csv)|*.xls;*.csv|All files (*.*)|*.*" ;
   ofd.FilterIndex = 0 ;
   ofd.RestoreDirectory = true ;

   if(ofd.ShowDialog() == System.Windows.Forms.DialogResult.OK)
   {
    return ofd.FileName;
   }
   return string.Empty;

注意：Microsoft Excel files (*.xls)|*.xls是一个整体，|前为显示说明信息，|后为文件类型；
如需同时过滤多个文件类型，文件类型间采用;分隔，如Microsoft Excel files (*.xls;*.csv)|*.xls;*.csv