C#文字的複製，剪切，撤銷

namespace WindowsFormsApplication1
{
    partial class Form1
    {
        /// <summary>
        /// 必需的設計器變量。
        /// </summary>
        private System.ComponentModel.IContainer components = null;

        /// <summary>
        /// 清理所有正在使用的資源。
        /// </summary>
        /// <param name="disposing">如果應釋放託管資源，爲 true；否則爲 false。</param>
        protected override void Dispose(bool disposing)
        {
            if (disposing && (components != null))
            {
                components.Dispose();
            }
            base.Dispose(disposing);
        }

        #region Windows 窗體設計器生成的代碼

        /// <summary>
        /// 設計器支持所需的方法 - 不要
        /// 使用代碼編輯器修改此方法的內容。
        /// </summary>
        private void InitializeComponent()
        {
            this.button1 = new System.Windows.Forms.Button();
            this.button2 = new System.Windows.Forms.Button();
            this.button3 = new System.Windows.Forms.Button();
            this.textBox1 = new System.Windows.Forms.TextBox();
            this.textBox2 = new System.Windows.Forms.TextBox();
            this.SuspendLayout();
            // 
            // button1
            // 
            this.button1.Location = new System.Drawing.Point(340, 60);
            this.button1.Name = "button1";
            this.button1.Size = new System.Drawing.Size(75, 23);
            this.button1.TabIndex = 0;
            this.button1.Text = "button1";
            this.button1.UseVisualStyleBackColor = true;
            this.button1.Click += new System.EventHandler(this.button1_Click);
            // 
            // button2
            // 
            this.button2.Location = new System.Drawing.Point(340, 134);
            this.button2.Name = "button2";
            this.button2.Size = new System.Drawing.Size(75, 23);
            this.button2.TabIndex = 1;
            this.button2.Text = "button2";
            this.button2.UseVisualStyleBackColor = true;
            this.button2.Click += new System.EventHandler(this.button2_Click);
            // 
            // button3
            // 
            this.button3.Location = new System.Drawing.Point(340, 215);
            this.button3.Name = "button3";
            this.button3.Size = new System.Drawing.Size(75, 23);
            this.button3.TabIndex = 2;
            this.button3.Text = "button3";
            this.button3.UseVisualStyleBackColor = true;
            this.button3.Click += new System.EventHandler(this.button3_Click);
            // 
            // textBox1
            // 
            this.textBox1.Location = new System.Drawing.Point(91, 61);
            this.textBox1.Name = "textBox1";
            this.textBox1.Size = new System.Drawing.Size(189, 21);
            this.textBox1.TabIndex = 3;
            // 
            // textBox2
            // 
            this.textBox2.Location = new System.Drawing.Point(91, 158);
            this.textBox2.Name = "textBox2";
            this.textBox2.Size = new System.Drawing.Size(189, 21);
            this.textBox2.TabIndex = 4;
            // 
            // Form1
            // 
            this.AutoScaleDimensions = new System.Drawing.SizeF(6F, 12F);
            this.AutoScaleMode = System.Windows.Forms.AutoScaleMode.Font;
            this.ClientSize = new System.Drawing.Size(484, 335);
            this.Controls.Add(this.textBox2);
            this.Controls.Add(this.textBox1);
            this.Controls.Add(this.button3);
            this.Controls.Add(this.button2);
            this.Controls.Add(this.button1);
            this.Name = "Form1";
            this.Text = "Form1";
            this.Load += new System.EventHandler(this.Form1_Load);
            this.ResumeLayout(false);
            this.PerformLayout();

        }

        #endregion

        private System.Windows.Forms.Button button1;
        private System.Windows.Forms.Button button2;
        private System.Windows.Forms.Button button3;
        private System.Windows.Forms.TextBox textBox1;
        private System.Windows.Forms.TextBox textBox2;
    }
}

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

namespace WindowsFormsApplication1
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void Form1_Load(object sender, EventArgs e)
        {
            button1.Text = "複製";
            button2.Text = "剪切";
            button3.Text = "撤銷";
            textBox1.Multiline = true;
            textBox2.Multiline = true;
            textBox1.Size = new Size(189, 50);
            textBox2.Size = new Size(189, 50);

        }

        private void button1_Click(object sender, EventArgs e)
        {
            textBox1.Select(textBox1.SelectionStart,textBox1.SelectionLength);
            textBox2.Text = textBox1.SelectedText;
        }
        private void button2_Click(object sender, EventArgs e)
        {
            textBox1.Select(textBox1.SelectionStart, textBox1.SelectionLength);
            textBox2.Text = textBox1.SelectedText;
            textBox1.Select(0, textBox1.SelectionStart-1);
            textBox1.Text = textBox1.SelectedText;
        }
        private void button3_Click(object sender, EventArgs e)
        {
            textBox2.Undo();
        }   
    }
}