public Form1()
        {
            InitializeComponent();
            SetEvents();
        }

        /// <summary>
        /// 注册事件
        /// </summary>
        void SetEvents()
        {
            foreach (Control ctl in this.groupBox.Controls)
            {
                if (ctl is TextBox)
                {
                    TextBox txtBox = ctl as TextBox;
                    txtBox.Click += new System.EventHandler(txtBox_Click);
                    txtBox.TextChanged += new EventHandler(txtBox_TextChanged);
                }
            }
        }

        private void txtBox_Click(object sender, EventArgs e)
        {
            //选中当前文本框所有文本
            //类似实现if(txtBox1.Focus())
            //               txtBox1.SelectAll();
        }

        private void txtBox_TextChanged(object sender, EventArgs e)
        {
            //文本框内文本改变触发事件
        }

Textbox textbox1 = (Textbox)sender;
switch(textbox1.name){
case "textbox1":{

}
}

------解决方案--------------------
查看sender参数

------解决方案--------------------
没问题。事件里面用sender获取执行的控件，如
TextBox txtBox = sender as TextBox;
if(txtBox.Focus())
   txtBox.SelectAll();