C# Mdi窗体：一个是不管点击多少次子窗体都只会弹出一个窗体，并且前置；两个窗体控件之间的联动，修改一个另外一个跟着作出相应的改变！

Program：

using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.Linq;
using System.Runtime.InteropServices;
using System.Threading;
using System.Windows.Forms;
namespace SASPGCalcBookTool
{
    public static class Program
    {
        public static int Msp { get; set; }
        [DllImport("user32.dll")]
        private static extern bool SetForegroundWindow(IntPtr hWnd);
        [DllImport("user32.dll")]
        private static extern bool ShowWindowAsync(IntPtr hWnd, int nCmdShow);
        [DllImport("user32.dll")]
        private static extern bool IsIconic(IntPtr hWnd);
        private const int SW_RESTORE = 9;
        /// <summary>
        /// c# 进程窗口显示并前置
        /// </summary>
        public static void RaiseOtherProcess()
        {
            Process proc = Process.GetCurrentProcess();
            Process.GetProcesses();
            foreach (Process otherProc in Process.GetProcessesByName(proc.ProcessName))
            {
                //ignore "this" process
                if (proc.Id != otherProc.Id)
                {
                    // Found a "same named process".
                    // Assume it is the one we want brought to the foreground.
                    // Use the Win32 API to bring it to the foreground.
                    IntPtr hWnd = otherProc.MainWindowHandle;
                    if (IsIconic(hWnd))
                    {
                        ShowWindowAsync(hWnd, 9);
                    }
                    SetForegroundWindow(hWnd);
                    break;
                }
            }
        }
        /// <summary>
        /// 应用程序的主入口点。
        /// </summary>
        [STAThread]
        static void Main()
        {
            Application.EnableVisualStyles();
            Application.SetCompatibleTextRenderingDefault(false);
            bool createdNew;
            Mutex instance = new Mutex(true, "MainFrm", out createdNew);
            if (createdNew)
            {
                Application.Run(new MainFrm());
                instance.ReleaseMutex();
                //如果需要窗体重启，并出现问题，将这句改为
                //instance.Dispose();
            }
            else
            {
                RaiseOtherProcess();
                Application.Exit();
            }
        }
    }
}

主窗体：

using SASPGCalcBookTool.SubFrms;
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
namespace SASPGCalcBookTool
{
    public partial class MainFrm : Form
    {
        public static Form Mdifrm { set; get; }
        public static Form Sdfrm { set; get; }
        public static Form Hdfrm { set; get; }
        public MainFrm()
        {
            InitializeComponent();
        }
        private void toolStripMenuItem2_Click(object sender, EventArgs e)
        {
            if (Mdifrm == null || Mdifrm.IsDisposed)
            {
                Mdifrm = new MainDataIn
                {
                    MdiParent = this
                };
                Mdifrm.Show();
            }
            else
            {
                if (Mdifrm.WindowState == FormWindowState.Minimized)
                {
                    Mdifrm.WindowState = FormWindowState.Normal;
                }
            }
            Mdifrm.Activate();
        }
        private void toolStripMenuItem3_Click(object sender, EventArgs e)
        {
            if (Sdfrm == null || Sdfrm.IsDisposed)
            {
                Sdfrm = new ShellData
                {
                    MdiParent = this
                };
                Sdfrm.Show();
            }
            else
            {
                if (Sdfrm.WindowState == FormWindowState.Minimized)
                {
                    Sdfrm.WindowState = FormWindowState.Normal;
                }
            }
            Sdfrm.Activate();
        }
    }
}

子窗体1：

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Text.RegularExpressions;
using System.Windows.Forms;
namespace SASPGCalcBookTool.SubFrms
{
    public partial class MainDataIn : Form
    {
        public int Msp { get; set; }
        public MainDataIn()
        {
            InitializeComponent();
        }
        private void MainDataIn_Load(object sender, EventArgs e)
        {
            MainShellPart.SelectedIndex = 0;
        }
        private void MainShellPart_SelectedIndexChanged(object sender, EventArgs e)
        {
            Program.Msp= int.Parse(MainShellPart.Text);
            if (MainFrm.Sdfrm == null || MainFrm.Sdfrm.IsDisposed)
            {
                return;
            }
            DataGridView ShlPartData = (DataGridView)MainFrm.Sdfrm.Controls["ShlPartData"];
            int rown = int.Parse(MainShellPart.Text), n = ShlPartData.Rows.Count;
            if (rown > n)
            {
                for (int i = n + 1; i <= rown; i++)
                {
                    int index = ShlPartData.Rows.Add();
                    ShlPartData.Rows[index].Cells[0].Value = "筒体段" + i;
                }
            }
            else if (rown < n)
            {
                for (int i = n; i > rown; i--)
                {
                    ShlPartData.Rows.RemoveAt(i-1);
                }
            }
        }
    }
}

子窗体2：

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using SASPGCalcBookTool.SubFrms;
namespace SASPGCalcBookTool.SubFrms
{
    public partial class ShellData : Form
    {
        public ShellData()
        {
            InitializeComponent();
        }
        private void ShellData_Load(object sender, EventArgs e)
        {
            for (int i = 1; i <= Program.Msp; i++)
            {
                int index = ShlPartData.Rows.Add();
                ShlPartData.Rows[index].Cells[0].Value = "筒体段" + i;
            }
        }
        public void _ChangShlPartDataRow(int rown)
        {
            int n = ShlPartData.Rows.Count;
            if (rown > n)
            {
                for (int i = n+1; i <= rown; i++)
                {
                    int index = ShlPartData.Rows.Add();
                    ShlPartData.Rows[index].Cells[0].Value = "筒体段" + i;
                }
            }
            else if (rown < n)
            {
                for (int i = n; i > rown; i--)
                {
                   ShlPartData.Rows.RemoveAt(i);
                }
            }
        }
    }
}