สอบถามเรื่องการให้ textBox.Text แสดงค่าอย่างต่อเนื่อง เป็นตัวเลขต่างๆต่อกัน

        protected void btnOne_Click(object sender, EventArgs e)
        {
            this.txtTexbox.Text = "1";
        }

        protected void btnTwo_Click(object sender, EventArgs e)
        {
            this.txtTexbox.Text = "12";
        }

protected void btnOne_Click(object sender, EventArgs e)
{
    this.txtTexbox.Text = "1";
}

protected void btnTwo_Click(object sender, EventArgs e)
{
    this.txtTexbox.Text &= "2";
}

protected void btnOne_Click(object sender, EventArgs e)
{
    this.txtTexbox.Text = "1";
}

protected void btnTwo_Click(object sender, EventArgs e)
{
    this.txtTexbox.Text += "2";
}

protected void btnOne_Click(object sender, EventArgs e)
{
    this.txtTexbox.Text += "1";
}

protected void btnTwo_Click(object sender, EventArgs e)
{
    this.txtTexbox.Text += "2";
}