Avoid postback when getting dropdownlist value c# asp

Question

I've dynamically created a dropdownlist within C# (No code in asp):

DropDownList myDDL = new DropDownList();

This can't be called from pageLoad() as it's not loaded everytime the page refreshes. However it's loaded everytime OnPostback(OnSelectedIndexChanged()) of another dll so I cant do !IsPostBack.

---

This dll is created when:

• A value of another dropdownlist populates a GridView using OnSelectedIndexChanged()

  <asp:DropDownList id ="select1" name="assignGetForm"  runat="server" class="selectClass" AutoPostBack="True" OnSelectedIndexChanged="populateGridView">
  

• On the GridView a function is run OnRowDatabound()(when the above OnIndexChanged() populates it) to populate myDDL inside the GridView

  <asp:GridView id="GridView1" name="GridView1" onrowdatabound="populateCellsDDL" runat="server"></asp:GridView>
  

I'm now trying to access the values in myDDL using a button onclick() event - however this always does postback and refreshes the page so myDDL dissapears and when I print the value to console it just gives my first value select activity and not the one i've actually selected.

How would I get these values when they are changed as this dll is not populated on pageLoad(). I've tried looking at AJAX however i'm unsure how to look at the c# value through this. I tried aswell viewstates but i dont have luck as again it doesnt populate on pageLoad().

Answer 1

I think, you need to rebind the grid in each postback, if you want to access values of dynamically created controls.

I tried to simulate the situation with below sample code and I was able to access the value successfully.

ASPX code

<asp:DropDownList ID="select1" name="assignGetForm" runat="server" class="selectClass" AutoPostBack="True" />
<asp:GridView ID="GridView1" name="GridView1" OnRowDataBound="GridView1_DataBound" runat="server" />
<asp:Button ID="Button1" runat="server" Text="Button" OnClick="Button1_Click" />

C# code behind

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

    if (!IsPostBack || GridView1.Rows.Count > 0)
        BindGrid();
}

private void FillMainDll()
{
    select1.DataSource = new int[] { 1, 2, 3 };
    select1.DataBind();
}

private void BindGrid()
{
    var dt = new DataTable();

    dt.Columns.Add(new DataColumn("ID", typeof(Int32)));
    dt.Columns.Add(new DataColumn("Name", typeof(string)));

    for (int i = 1; i < 5; i++)
    {
        DataRow dr = dt.NewRow();

        dr[0] = i;
        dr[1] = "Name - " + i.ToString();

        dt.Rows.Add(dr);
    }

    GridView1.DataSource = dt;
    GridView1.DataBind();
}

protected void GridView1_DataBound(object sender, GridViewRowEventArgs e)
{
    if (e.Row.RowType == DataControlRowType.DataRow)
    {
        var myDDL = new DropDownList();
        myDDL.ID = "myDDL";
        myDDL.DataSource = GetGridRowDdlData();
        myDDL.DataBind();
        e.Row.Cells[1].Controls.Add(myDDL);
    }
}

private IEnumerable<string> GetGridRowDdlData()
{
    var data = new List<string>();

    for (int i = 1; i < 4; i++)
    {
        data.Add("Name - " + i * int.Parse(select1.SelectedValue));
    }

    return data;
}

protected void Button1_Click(object sender, EventArgs e)
{
    var sb = new System.Text.StringBuilder();

    foreach (GridViewRow row in GridView1.Rows)
    {
        var myDDL = row.FindControl("myDDL") as DropDownList;
        if (myDDL != null)
        {
            sb.AppendFormat("{0}<br/>", myDDL.SelectedValue);
        }
    }

    Response.Write(sb.ToString());
}