限制打开一个应用程序，多次打开则显示界面

阻止程序多次重复运行，多次点击会显示原界面

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading;
using System.Windows.Forms;

namespace WindowsFormsApplication1
{
    public partial class Form1 : Form
    {
        public Form1（）
        {
            InitializeComponent（）;
            Thread.Sleep（1000）;
        }
    }
}

 属性            大小     日期    时间   名称
----------- ---------  ---------- -----  ----
     目录           0  2019-08-10 08:53  WindowsFormsApplication1\
     目录           0  2019-08-10 08:53  WindowsFormsApplication1\.vs\
     目录           0  2019-08-10 08:53  WindowsFormsApplication1\.vs\WindowsFormsApplication1\
     目录           0  2019-08-10 08:53  WindowsFormsApplication1\.vs\WindowsFormsApplication1\v14\
     文件       35328  2019-08-10 09:28  WindowsFormsApplication1\.vs\WindowsFormsApplication1\v14\.suo
     目录           0  2019-08-10 09:27  WindowsFormsApplication1\WindowsFormsApplication1\
     文件        1039  2019-08-10 08:53  WindowsFormsApplication1\WindowsFormsApplication1.sln
     目录           0  2019-08-10 08:53  WindowsFormsApplication1\WindowsFormsApplication1\bin\
     目录           0  2019-08-10 08:55  WindowsFormsApplication1\WindowsFormsApplication1\bin\Debug\
     文件        9216  2019-08-10 09:27  WindowsFormsApplication1\WindowsFormsApplication1\bin\Debug\WindowsFormsApplication1.exe
     文件       22016  2019-08-10 09:27  WindowsFormsApplication1\WindowsFormsApplication1\bin\Debug\WindowsFormsApplication1.pdb
     文件       22688  2019-08-11 01:04  WindowsFormsApplication1\WindowsFormsApplication1\bin\Debug\WindowsFormsApplication1.vshost.exe
     文件         490  2018-04-12 07:35  WindowsFormsApplication1\WindowsFormsApplication1\bin\Debug\WindowsFormsApplication1.vshost.exe.manifest
     文件         432  2019-08-10 09:00  WindowsFormsApplication1\WindowsFormsApplication1\Form1.cs
     文件        1417  2019-08-10 08:55  WindowsFormsApplication1\WindowsFormsApplication1\Form1.Designer.cs
     文件        5817  2019-08-10 08:55  WindowsFormsApplication1\WindowsFormsApplication1\Form1.resx
     目录           0  2019-08-10 08:53  WindowsFormsApplication1\WindowsFormsApplication1\obj\
     目录           0  2019-08-10 08:55  WindowsFormsApplication1\WindowsFormsApplication1\obj\Debug\
     文件        1020  2019-08-10 08:55  WindowsFormsApplication1\WindowsFormsApplication1\obj\Debug\DesignTimeResolveAssemblyReferences.cache
     文件        7042  2019-08-11 01:04  WindowsFormsApplication1\WindowsFormsApplication1\obj\Debug\DesignTimeResolveAssemblyReferencesInput.cache
     目录           0  2019-08-10 08:53  WindowsFormsApplication1\WindowsFormsApplication1\obj\Debug\TempPE\
     文件        1242  2019-08-11 01:05  WindowsFormsApplication1\WindowsFormsApplication1\obj\Debug\WindowsFormsApplication1.csproj.FileListAbsolute.txt
     文件        1012  2019-08-10 08:55  WindowsFormsApplication1\WindowsFormsApplication1\obj\Debug\WindowsFormsApplication1.csproj.GenerateResource.Cache
     文件        2210  2019-08-10 08:55  WindowsFormsApplication1\WindowsFormsApplication1\obj\Debug\WindowsFormsApplication1.csprojResolveAssemblyReference.cache
     文件        9216  2019-08-10 09:27  WindowsFormsApplication1\WindowsFormsApplication1\obj\Debug\WindowsFormsApplication1.exe
     文件         180  2019-08-10 08:55  WindowsFormsApplication1\WindowsFormsApplication1\obj\Debug\WindowsFormsApplication1.Form1.resources
     文件       22016  2019-08-10 09:27  WindowsFormsApplication1\WindowsFormsApplication1\obj\Debug\WindowsFormsApplication1.pdb
     文件         180  2019-08-10 08:55  WindowsFormsApplication1\WindowsFormsApplication1\obj\Debug\WindowsFormsApplication1.Properties.Resources.resources
     文件        2032  2019-08-10 09:27  WindowsFormsApplication1\WindowsFormsApplication1\Program.cs
     目录           0  2019-08-10 08:53  WindowsFormsApplication1\WindowsFormsApplication1\Properties\
     文件        1370  2019-08-10 08:53  WindowsFormsApplication1\WindowsFormsApplication1\Properties\AssemblyInfo.cs
............此处省略6个文件信息