Retrieve data from dynamically created controls

Question

I am dynamically creating several dropdown list on the selection changed event of a main (static) dropdown list. These are created in The TableCell of default Table. When submit button is clicked I need to load a new page with selected values of dropdown as parameters. Basically I need to get the dropdown results in the second page.

This is how dropboxes are created:

    while (reader.Read())
    { 
        pcID = int.Parse(reader["fk_pcID"].ToString());
        pcDesc = GetpcDescription(pcID);
        List<Product> prodList = GetProductsBypcID(pcID);
        DropDownList ddList = new DropDownList();
        ddList.ID = "ddlPC" + pcID;
        foreach(Product prod in prodList)
        {
            ddList.Items.Add(new ListItem(prod.ProductName, prod.ProductID.ToString()));
        }
        TableCell cell1 = new TableCell();
        cell1.Text = pcDesc;

        TableCell cell2 = new TableCell();
        cell2.Controls.Add(ddList);

        TableRow row = new TableRow();
        row.Cells.Add(cell1);
        row.Cells.Add(cell2);

        table.Rows.Add(row);  
    }

EDIT: The above code runs at the selection changed event of a dropdown which is set to runat server. But dynamically created dropdowns are not set to run at server

Please don't prefix questions with "ASP.NET:". On Stack Overflow, we use tags to categorize questions. — John Saunders
– John Saunders, Commented Aug 30, 2011 at 16:30
if you're having problems retrieving the values on postback, chances are you are creating your dynamic controls too late in your page lifecycle. Try adding them when your webform is initialized (OnInit) — Paolo Falabella
– Paolo Falabella, Commented Aug 30, 2011 at 16:37

Michael Jasper · Accepted Answer · 2011-08-30 16:37:08Z

1

Are these drop-down boxes runat="server"? Meaning: did you created them programmaticly via a .net post-back event through the code behind? If so, just get the selected value the same as you would with any other control, and then pass it through a query string or a cookie.

Are these standard html drop-down lists? Good luck reading them from a code-behind. That gets you all tangled up in the viewstate, and while technically possible, is realistically not feasible.

If the second option is the case, it might be a much better option to have your button target a JavaScript function that gets the selected values and then passes them via querystring. Then on the other page you can read the querystrings from the code-behind, or on the client-side.

answered Aug 30, 2011 at 16:37

Michael Jasper

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3 Comments

James Johnson Over a year ago

No, putting the selected value in a cookie is a horrible idea. This can be handled with a proper understanding of the page lifecycle.

smatter Over a year ago

The above code runs at the selection changed event of a dropdown which is set to runat server. But dynamically created dropdowns are not set to run at server.

Michael Jasper Over a year ago

Why is this a horrible idea? Example: "Select your Language [english, spanish, german]" Would not a cookie be the best place for this type of information? He doesn't give any clues about the content of the dropdown (until edit). So a cookie is an equally valid way as any to store data across pages.

James Johnson · Accepted Answer · 2011-08-30 16:51:17Z

0

This sounds like a good candidate for the DynamicControlsPlaceholder. It will preserve your dynamic controls automatically, without requiring any additional code on the page. If you need to create the controls OnSelectedIndexChanged, I think this might be the simplest solution.

It's a free component, and you can download it here.

http://www.denisbauer.com/ASPNETControls/DynamicControlsPlaceholder.aspx

answered Aug 30, 2011 at 16:51

James Johnson

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