Dynamic rows & controls in a table - problem

[JohnS]

Hi!

I'm trying to create a page with dynamic controls, and I'm having difficulty wrt the liffe cycle.

The page has some static controls, but also a table which has dynamic rows, cells of which contain dynamic controls, including a DropDownList.

The idea is that the page has an "Add" button, which should result in a new row being added to the table. The selected values in the earlier DropDownLists must be preserved.

So, first time the page looks like:

[Static Controls]
[TableRow1 [DropDownList1]]
[Add Button]

Clicking the button should result in:

[Static Controls]
[TableRow1 [DropDownList1]]
[TableRow2 [DropDownList2]]
[Add Button]

with DropDownList1 selection being preserved.

The Button click event code tries to read the current selections of the DDLs and store them in session, It then causes a redirect to the same page, forcing the page to be drawn as new (from the life cycle point of view).

My sequence of code is:

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

where populate() sets up the static controls with data retrieved from a database (first time) or session (subsequently), and

populateVolatile() creates and fills the dynamic controls depending on the session data, including DDL selections.

It contains the code:

// add each type/num info to table
        foreach (TypeNumInfo tni in volInfo.typeNumRows) {
            TableRow tr = new TableRow();

            // index number
            TableCell tc1 = new TableCell();
            tc1.Text = tni.idx.ToString();
            tr.Cells.Add(tc1);

            // add a DDL
            TableCell tc2 = new TableCell();
            DropDownList ddl = new DropDownList();

            // add ID and list data
            ddl.ID = "ddl" + tni.idx;
            foreach (ListItem li in dTypes) {
                ddl.Items.Add(li);
            }

            // set the selected
            // TODO not working
            ddl.SelectedIndex = tni.typeSel;

            tc2.Controls.Add(ddl);
            tr.Cells.Add(tc2);

            tblTypeNum.Rows.Add(tr);
        }

The button click code is as follows:

protected void bAddTypeNum_Click(object sender, EventArgs e) {
        // get dept, applies selections from static controls
        statInfo.selDept = ddlDept.SelectedIndex;
        statInfo.selApplies = ddlApplies.SelectedIndex;

        // create new type/num info representing tablerow data
        TypeNumInfo tni = new TypeNumInfo();
        int lastIdx = volInfo.typeNumRows.Count;
        tni.idx = lastIdx + 1;

        // add to list
        volInfo.typeNumRows.Add(tni);

        // cache previous rows
        int i = 0;
        foreach (TableRow tr in tblTypeNum.Rows) {
            // if row has droplist, i.e. more than 1 cell
            if (tr.Cells.Count > 1) {
                DropDownList ddl = (DropDownList)tr.Cells[1].Controls[0];

                // get the selection in that row
                // TODO not working reliably
                volInfo.typeNumRows[i++].typeSel = ddl.SelectedIndex;
            }
        }

        // update session
        Session[strStat] = statInfo;
        Session[strVol] = volInfo;

        // draw as new page
        Response.Redirect("");
    }

I know the redirect creates an extra trip to the server, but I couldn't find a useful way to enable redrawing after the button event.

Everything works fine except for the DDL selection handling - I cannot set or correctly read the selections.

Help!

John