How to use a memory-mapped file with C# in WinCE

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Text;
using System.Windows.Forms;
using Common.WinCEAPI;
using System.Runtime.InteropServices;
using LPIGeneral;
using LPISerializeData;

namespace ShareB
{
    public partial class frmMain : Form
    {
        const string MapName = "OrzCloud";
        const int MapSize = 1024;
        IntPtr m_pMapFile;
        IntPtr m_pBuff;

        public frmMain()
        {
            InitializeComponent();
            m_pMapFile = IntPtr.Zero;
            m_pBuff = IntPtr.Zero;
        }

        private void btnGet_Click(object sender, EventArgs e)
        {
            int t_i4Error = 0;
            try
            {
                if (m_pMapFile == IntPtr.Zero)
                {
                    // open map file
                    //m_pMapFile = WinCE.CreateFileMapping(WinCEConst.INVALID_HANDLE_VALUE, null,
                    //    WinCEConst.PAGE_READWRITE, 0, 0, MapName);
                    m_pMapFile = WinCE.OpenFileMapping(WinCEConst.FILE_MAP_ALL_ACCESS, false, MapName);
                    // check error code
                    t_i4Error = Marshal.GetLastWin32Error();

                    // get map file
                    m_pBuff = WinCE.MapViewOfFile(m_pMapFile, WinCEConst.FILE_MAP_ALL_ACCESS, 0, 0, MapSize);
                }

                byte[] bytData = new byte[MapSize];
                // read data from map file
                Marshal.Copy(m_pBuff, bytData, 0, MapSize);
                // change byte array to string
                txtData.Text = Encoding.ASCII.GetString(bytData,0,MapSize).Trim();
            }
            catch (Exception ex)
            {
                t_i4Error = Marshal.GetLastWin32Error();
                MessageBox.Show(ex.Message);
            }
        }

        private void frmMain_Closing(object sender, CancelEventArgs e)
        {
            try
            {
                WinCE.UnmapViewOfFile(m_pBuff);
                WinCE.CloseHandle(m_pMapFile);
            }
            catch (Exception ex)
            {
                MessageBox.Show(ex.Message);
            }
        }
    }
}