【C#】ストップウォッチで処理途中の時間を取得する

namespace WinFormsApp2
{
    partial class Form1
    {
        /// <summary>
        ///  Required designer variable.
        /// </summary>
        private System.ComponentModel.IContainer components = null;

        /// <summary>
        ///  Clean up any resources being used.
        /// </summary>
        /// <param name="disposing">true if managed resources should be disposed; otherwise, false.</param>
        protected override void Dispose(bool disposing)
        {
            if (disposing && (components != null))
            {
                components.Dispose();
            }
            base.Dispose(disposing);
        }

        #region Windows Form Designer generated code

        /// <summary>
        ///  Required method for Designer support - do not modify
        ///  the contents of this method with the code editor.
        /// </summary>
        private void InitializeComponent()
        {
            textBox1 = new TextBox();
            button1 = new Button();
            textBox2 = new TextBox();
            label1 = new Label();
            label2 = new Label();
            textBox3 = new TextBox();
            label3 = new Label();
            SuspendLayout();
            // 
            // textBox1
            // 
            textBox1.Font = new Font("Yu Gothic UI", 11.25F);
            textBox1.Location = new Point(154, 37);
            textBox1.Name = "textBox1";
            textBox1.Size = new Size(138, 27);
            textBox1.TabIndex = 0;
            // 
            // button1
            // 
            button1.Location = new Point(154, 4);
            button1.Name = "button1";
            button1.Size = new Size(138, 27);
            button1.TabIndex = 1;
            button1.Text = "button1";
            button1.UseVisualStyleBackColor = true;
            button1.Click += button1_Click;
            // 
            // textBox2
            // 
            textBox2.Font = new Font("Yu Gothic UI", 11.25F);
            textBox2.Location = new Point(154, 70);
            textBox2.Name = "textBox2";
            textBox2.Size = new Size(138, 27);
            textBox2.TabIndex = 2;
            // 
            // label1
            // 
            label1.AutoSize = true;
            label1.Font = new Font("Yu Gothic UI", 14.25F, FontStyle.Regular, GraphicsUnit.Point, 128);
            label1.Location = new Point(12, 37);
            label1.Name = "label1";
            label1.Size = new Size(119, 25);
            label1.TabIndex = 3;
            label1.Text = "開始～処理A";
            // 
            // label2
            // 
            label2.AutoSize = true;
            label2.Font = new Font("Yu Gothic UI", 14.25F, FontStyle.Regular, GraphicsUnit.Point, 128);
            label2.Location = new Point(13, 103);
            label2.Name = "label2";
            label2.Size = new Size(107, 25);
            label2.TabIndex = 4;
            label2.Text = "開始～終了";
            // 
            // textBox3
            // 
            textBox3.Font = new Font("Yu Gothic UI", 11.25F);
            textBox3.Location = new Point(154, 103);
            textBox3.Name = "textBox3";
            textBox3.Size = new Size(138, 27);
            textBox3.TabIndex = 5;
            // 
            // label3
            // 
            label3.AutoSize = true;
            label3.Font = new Font("Yu Gothic UI", 14.25F, FontStyle.Regular, GraphicsUnit.Point, 128);
            label3.Location = new Point(12, 70);
            label3.Name = "label3";
            label3.Size = new Size(118, 25);
            label3.TabIndex = 6;
            label3.Text = "開始～処理B";
            // 
            // Form1
            // 
            AutoScaleDimensions = new SizeF(7F, 15F);
            AutoScaleMode = AutoScaleMode.Font;
            ClientSize = new Size(304, 141);
            Controls.Add(label3);
            Controls.Add(textBox3);
            Controls.Add(label2);
            Controls.Add(label1);
            Controls.Add(textBox2);
            Controls.Add(button1);
            Controls.Add(textBox1);
            Name = "Form1";
            Text = "Form1";
            ResumeLayout(false);
            PerformLayout();
        }

        #endregion

        private TextBox textBox1;
        private Button button1;
        private TextBox textBox2;
        private Label label1;
        private Label label2;
        private TextBox textBox3;
        private Label label3;
    }
}

using System.Diagnostics;

namespace WinFormsApp2
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void button1_Click(object sender, EventArgs e)
        {
            // Stopwatchインスタンスの作成
            Stopwatch stopwatch = new();

            // 計測開始
            stopwatch.Start();

            // 時間を計測したい処理
            Thread.Sleep(1000);

            // 計測時間を表示（処理開始～処理Aまで）
            textBox1.Text = stopwatch.Elapsed.ToString();

            // 時間を計測したい処理
            Thread.Sleep(3000);

            // 計測時間を表示（処理開始～処理Bまで）
            textBox2.Text = stopwatch.Elapsed.ToString();

            // 時間を計測したい処理
            Thread.Sleep(5000);

            // 計測終了
            stopwatch.Stop();

            // 計測時間を表示（処理開始～処理終了まで）
            textBox3.Text = stopwatch.Elapsed.ToString();
        }
    }
}