System.Windows.Forms.OpenFileDialog openFileDialog;
            openFileDialog = new OpenFileDialog();
            //初始显示目录
            openFileDialog.InitialDirectory = @"C:\";
            //下次打开对话框是否定位到上次打开的目录
            openFileDialog.RestoreDirectory = true;
            //过滤文件类型
            openFileDialog.Filter = "map documents(*.mxd)|*.mxd|所有文件 (*.*)|*.*";
            //FilterIndex 与 Filter 关联对应，用于设置默认显示的文件类型
            openFileDialog.FilterIndex = 1;//默认是1，则默认显示的文件类型为*.mxd；如果设置为2，则默认显示的文件类型是*.*
            if (openFileDialog.ShowDialog() == DialogResult.OK)
            {
                if (System.IO.File.Exists(Application.StartupPath + openFileDialog.FileName))
                {
                    m_pApp.LoadMxd(Application.StartupPath + openFileDialog.FileName, "", 0);

                }
            }