有一道题完全不会，求大神帮助，明天就考试了T T

using System;
using System.Threading;
using System.Windows.Forms;

namespace WindowsFormsApplication1
{
    public partial class Form1 : Form
    {
        private System.Threading.Timer timer;
        private Random random;
        private SynchronizationContext context;

        public Form1()
        {
            InitializeComponent();
            random = new Random();
            timer = new System.Threading.Timer(CreadeRandom, null, Timeout.Infinite, Timeout.Infinite);
            context = SynchronizationContext.Current;
        }

        private void CreadeRandom(object obj)
        {
            context.Post((t) => { listBox1.Items.Add(random.Next(1, 101)); }, obj);
        }

        private void button1_Click(object sender, EventArgs e)
        {
            listBox1.Items.Clear();
            listBox1.Items.Add("随机数生成开始！");
            timer.Change(0, int.Parse(textBox1.Text));
        }

        private void button2_Click(object sender, EventArgs e)
        {
            timer.Change(Timeout.Infinite, Timeout.Infinite);
            listBox1.Items.Add("随机数生成结束！");
            
        }
    }
}

namespace WindowsFormsApplication1
{
    partial class Form1
    {
        /// <summary>
        /// 必需的设计器变量。
        /// </summary>
        private components = null;

        /// <summary>
        /// 清理所有正在使用的资源。
        /// </summary>
        /// <param name="disposing">如果应释放托管资源，为 true；否则为 false。</param>
        protected override void Dispose(bool disposing)
        {
            if (disposing && (components != null))
            {
                components.Dispose();
            }
            base.Dispose(disposing);
        }

        #region Windows 窗体设计器生成的代码

        /// <summary>
        /// 设计器支持所需的方法 - 不要
        /// 使用代码编辑器修改此方法的内容。
        /// </summary>
        private void InitializeComponent()
        {
            this.components = new ();
            this.serialPort1 = new (this.components);
            this.label1 = new System.Windows.Forms.Label();
            this.textBox1 = new System.Windows.Forms.TextBox();
            this.button1 = new System.Windows.Forms.Button();
            this.button2 = new System.Windows.Forms.Button();
            this.listBox1 = new System.Windows.Forms.ListBox();
            this.SuspendLayout();
            //
            // label1
            //
            this.label1.AutoSize = true;
            this.label1.Location = new System.Drawing.Point(22, 29);
            this.label1.Name = "label1";
            this.label1.Size = new System.Drawing.Size(137, 12);
            this.label1.TabIndex = 0;
            this.label1.Text = "生成时间间隔（毫秒）：";
            //
            // textBox1
            //
            this.textBox1.Location = new System.Drawing.Point(165, 26);
            this.textBox1.Name = "textBox1";
            this.textBox1.Size = new System.Drawing.Size(100, 21);
            this.textBox1.TabIndex = 1;
            this.textBox1.Text = "1000";
            //
            // button1
            //
            this.button1.Location = new System.Drawing.Point(291, 24);
            this.button1.Name = "button1";
            this.button1.Size = new System.Drawing.Size(75, 23);
            this.button1.TabIndex = 2;
            this.button1.Text = "开始";
            this.button1.UseVisualStyleBackColor = true;
            this.button1.Click += new System.EventHandler(this.button1_Click);
            //
            // button2
            //
            this.button2.Location = new System.Drawing.Point(372, 24);
            this.button2.Name = "button2";
            this.button2.Size = new System.Drawing.Size(75, 23);
            this.button2.TabIndex = 3;
            this.button2.Text = "停止";
            this.button2.UseVisualStyleBackColor = true;
            this.button2.Click += new System.EventHandler(this.button2_Click);
            //
            // listBox1
            //
            this.listBox1.FormattingEnabled = true;
            this.listBox1.ItemHeight = 12;
            this.listBox1.Location = new System.Drawing.Point(39, 80);
            this.listBox1.Name = "listBox1";
            this.listBox1.Size = new System.Drawing.Size(475, 340);
            this.listBox1.TabIndex = 4;
            //
            // Form1
            //
            this.AutoScaleDimensions = new System.Drawing.SizeF(6F, 12F);
            this.AutoScaleMode = System.Windows.Forms.AutoScaleMode.Font;
            this.ClientSize = new System.Drawing.Size(550, 453);
            this.Controls.Add(this.listBox1);
            this.Controls.Add(this.button2);
            this.Controls.Add(this.button1);
            this.Controls.Add(this.textBox1);
            this.Controls.Add(this.label1);
            this.Name = "Form1";
            this.Text = "Form1";
            this.ResumeLayout(false);
            this.PerformLayout();

        }

        #endregion

        private serialPort1;
        private System.Windows.Forms.Label label1;
        private System.Windows.Forms.TextBox textBox1;
        private System.Windows.Forms.Button button1;
        private System.Windows.Forms.Button button2;
        private System.Windows.Forms.ListBox listBox1;

    }
}