设置文本框高亮显示

一般常常会设置高亮选中，供用户重新输入：

        private void textBox1_MouseDown(object sender, MouseEventArgs e)
        {

            //No.1
            string str = this.textBox1.Text;
            if (!string.IsNullOrEmpty(str) && !string.IsNullOrEmpty(str.Trim()))      
            {
                str = str.Trim();
                this.textBox1.SelectionStart = 0;  //设置选中的开始为止
                this.textBox1.SelectionLength = this.textBox1.Text.Length; //设置选中文本长度

                //No.2

                //this.textBox1.Select(0,this.textBox1.Text.Length);
                //this.textBox1.SelectAll();       

                this.textBox1.Focus();
            }

         }