asp.net的DropDownList的使用

 protected void Page_Load(object sender, EventArgs e)
    {
        private string selectCourse;
        if (!IsPostBack)
        {
          
            TextBox1.Text = "20";
            TextBox2.Text = "80";
            
        }
        selectCourse = DropDownList1.SelectedItem.Value;
    }
protected void DropDownList1_SelectedIndexChanged1(object sender, EventArgs e)
    {
        if (selectCourse == DropDownList1.SelectedItem.Value)
        {
            return;
        }
        else
        {
            selectCourse = DropDownList1.SelectedItem.Value;
        }
    }