this.textBox1.Location = new System.Drawing.Point(12, 5);
this.textBox1.Multiline = true;
this.textBox1.Name = "textBox1";
this.textBox1.Size = new System.Drawing.Size(548, 188);
this.textBox1.TabIndex = 0;
this.textBox1.TextChanged += new System.EventHandler(this.textBox1_TextChanged);
this.textBox1.KeyDown += new System.Windows.Forms.KeyEventHandler(this.textBox1_KeyDown);//添加鍵盤事件

public Form1()
        {
            InitializeComponent();
            textBox1.TextChanged += new EventHandler(textBox1_TextChanged);
            textBox1.KeyDown+=new KeyEventHandler(textBox1_KeyDown);//添加鍵盤事件
        }

        /// <summary>
        /// 控件事件
        /// </summary>
        /// <param name="sender"></param>
        /// <param name="e"></param>
        private void textBox1_KeyDown(object sender, System.Windows.Forms.KeyEventArgs e)
        {
            if (e.KeyCode == Keys.A && e.Control)
            {
                textBox1.SelectAll();
            }
        }