C# 定时无操作则退出登陆，回到登陆界面。

有时候根据需求需要为程序添加在规定的时间内无操作则退出当前的登陆程序的功能，如下代码模拟描述的需求功能。

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Text;
using System.Windows.Forms;
using System.Runtime.InteropServices;

namespace LockScreenMsg
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
            label1.Height = 200;
        }

        [StructLayout(LayoutKind.Sequential)]
        struct LASTINPUTINFO
        {
            [MarshalAs(UnmanagedType.U4)]
            public int cbSize;
            [MarshalAs(UnmanagedType.U4)]
            public uint dwTime;
        }

        [DllImport("user32.dll")]
        static extern bool GetLastInputInfo(ref LASTINPUTINFO plii);

        static long GetLastInputTime()
        {
            LASTINPUTINFO vLastInputInfo = new LASTINPUTINFO();
            vLastInputInfo.cbSize = Marshal.SizeOf(vLastInputInfo);
            if (!GetLastInputInfo(ref vLastInputInfo))
            {
                return 0;
            }
            return Environment.TickCount - (long)vLastInputInfo.dwTime;
        }

        private void Form1_Load(object sender, EventArgs e)
        {
            timer1.Enabled = true;
        }

        public string isNull = null;
        private void timer1_Tick(object sender, EventArgs e)
        {
           long time=GetLastInputTime()/1000;
            
            this.label1.Text = string.Format("用户已经{0}秒没有操作了", time);
           if (time >= 20)
           {
                this.Close();
           }
        }
    }
}