Issue in my cascading dropdownlist

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C#

C#4.0

ASP.NET4

I am having three dropdowns,

in first dropdown i am binding values from db directly,

<asp:DropDownList ID="DropDownList1" runat="server" AutoPostBack="True" CssClass="DropDown"
                        Width="190px" OnSelectedIndexChanged="DropDownList1_SelectedIndexChanged">
                    </asp:DropDownList>

protected void Page_Load(object sender, EventArgs e)
    {
        if (!IsPostBack)
        {
            DropDown1ListView();
        }

    }

private void DropDown1ListView()
    {
        SqlConnection pCnn = new SqlConnection(Connection.Con);
        SqlDataAdapter da = new SqlDataAdapter("exec usp_dropdownlevel", pCnn);
        DataSet ds = new DataSet();
        pCnn.Open();
        da.Fill(ds);
        pCnn.Close();
        if (ds.Tables[0].Rows.Count > 0)
        {
            DropDownList1.DataSource = ds.Tables[0];
            DropDownList1.DataTextField = "Name";
            DropDownList1.DataValueField = "Code";
            DropDownList1.DataBind();
            DropDownList1.Items.Insert(0, "---Select---");
        }
    }

protected void DropDownList1_SelectedIndexChanged(object sender, EventArgs e)
    {
        string level = DropDownList1.SelectedItem.ToString();
        DropDown2(level);
        DropDownList3.SelectedIndex = 0;
    }

To bind second dropdown i have to get data from dropdown1

<asp:DropDownList ID="DropDownList2" runat="server" AutoPostBack="True" CssClass="DropDown"
                       Width="190px" OnSelectedIndexChanged="DropDownList2_SelectedIndexChanged">
                   </asp:DropDownList>

private void DropDownList2(string level)
    {
        SqlConnection pCnn = new SqlConnection(Connection.Con);
        SqlDataAdapter da = new SqlDataAdapter("exec usp_dropdownarea'" + level + "'", pCnn);
        DataSet ds = new DataSet();
        pCnn.Open();
        da.Fill(ds);
        pCnn.Close();
        if (ds.Tables[0].Rows.Count > 0)
        {
            DropDownList2.DataSource = ds.Tables[0];
            DropDownList2.DataTextField = "Name";
            DropDownList2.DataValueField = "Code";
            DropDownList2.DataBind();
            DropDownList2.Items.Insert(0, "---Select Area---");
        }
    }

protected void DropDownList2_SelectedIndexChanged(object sender, EventArgs e)
   {
       string area = DropDownList2.SelectedItem.ToString();
       DropDown3(area);
   }

To bind third dropdown i have to get data from dropdown2

<asp:DropDownList ID="DropDown3" runat="server" CssClass="DropDown" Width="190px">
                    </asp:DropDownList>

private void DropDown3(string area)
   {
       SqlConnection pCnn = new SqlConnection(Connection.Con);
       SqlDataAdapter da = new SqlDataAdapter("exec usp_DropDown3'" + area + "'", pCnn);
       DataSet ds = new DataSet();
       pCnn.Open();
       da.Fill(ds);
       pCnn.Close();
       if (ds.Tables[0].Rows.Count > 0)
       {
           DropDown3.DataSource = ds.Tables[0];
           DropDown3.DataTextField = "Name";
           DropDown3.DataValueField = "Code";
           DropDown3.DataBind();
           DropDown3.Items.Insert(0, "---Select Subject---");
       }
   }

The issue in this code is dropdown 1 is binding correctly but selecting values in dropdown2 is not changing, first value of the dropdown2 is getting select automatically even if i select some other values from dropdown2