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Why is my dynamic bound dropdown losing its value?

Posted on 2008-10-24
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Last Modified: 2010-05-18
I have a form that is created dynamically based on a widget type selected, e.g. Article Widget.  The widget will then tell the code what controls need to be created in the grid, e.g. in this example its 6 dropdown lists, 3 for the categories and 3 for the pages - these are paired together.

Now I can bind it fine, and all the dropdowns appear correctly.  All the category dropdowns have the correct details in, and the page dropdowns each have the first item set to "select a category".  All good so far.

I select the first dropdown and the event that I added to the dynamically bound dropdown correctly fires e.g. ddlCategory.SelectedIndexChanged += new EventHandler(pageCategory_SelectedIndexChanged); and its paired dropdown correctly gets filled with the pages for that category.  All other dropdowns at this point are still in their initial state.  So all controls are being rebuilt on postback, and the viewstate for the category dropdown is being remebered.  Again all good so far.

Now when I select a category in one of the other category dropdowns the SelectedIndexChanged event fires for both the first category dropdown and then the second dropdown.  This again I believe is correct behaviour, so that the page dropdowns can then have the correct items in them to allow the viewstate to be put back correctly.  However the first page dropdownlist loses its selected value - as if the viewstate is not being populated back.

Has anyone come across this before?
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Question by:ezekial316
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Author Comment

by:ezekial316
ID: 22794363
This controls are all being bound in a repeater so I thought I should add the repeater bound event.
protected void rptControls_ItemDataBound(object sender, RepeaterItemEventArgs e)
    {
        if (e.Item.ItemType == ListItemType.AlternatingItem || e.Item.ItemType == ListItemType.Item)
        {
            CMS_ControlMeta meta = (CMS_ControlMeta)e.Item.DataItem;
 
            switch (meta.InputType)
            {                
                case WidgetPropertyInformation.InputTypes.PageSelector: //page selector
 
                    DropDownList ddlFirst = new DropDownList();
                    DropDownList ddlSecond = new DropDownList();
 
                    CMS_CategoryService service = new CMS_CategoryService();
                    
                    ddlFirst.CssClass = "control";                    
                    ddlFirst.AutoPostBack = true;
                    
                    ddlFirst.SelectedIndexChanged += new EventHandler(pageCategory_SelectedIndexChanged);
                    
                    ddlFirst.ID = "ddlFirst" + e.Item.ItemIndex.ToString();
                    ddlFirst.DataSource = service.FetchCategoryTree();
                    ddlFirst.DataTextField = "Title";
                    ddlFirst.DataValueField = "ID";
                    ddlFirst.DataBind();
                    ddlFirst.Items.Insert(0, new ListItem("select", "select"));
 
                    (e.Item.FindControl("litLabel") as Literal).Text = meta.Name;
 
                    e.Item.FindControl("pair").Visible = true;
 
                    ddlSecond.ID = "ddlSecond" + e.Item.ItemIndex.ToString();
                    ddlSecond.CssClass = "control";                    
 
                    (e.Item.FindControl("litPair") as Literal).Text = "Select Page";
                    (e.Item.FindControl("phControls") as PlaceHolder).Controls.Add(ddlFirst);
                    (e.Item.FindControl("phControls2") as PlaceHolder).Controls.Add(ddlSecond);
 
                    break;                
            }
 
 
        }
    }

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Author Comment

by:ezekial316
ID: 22794367
And here is the code for the Item Selected Event
protected void pageCategory_SelectedIndexChanged(object sender, EventArgs e)
    {
        DropDownList ddl = sender as DropDownList;
        if (ddl != null)
        {
            RepeaterItem item = ddl.Parent.Parent as RepeaterItem;
            DropDownList ddl2 = (DropDownList)item.FindControl("ddlSecond" + item.ItemIndex.ToString());
 
            string id = ddl.ID;
 
            CMS_PageService service = new CMS_PageService();
            List<CMS_Page> pages = service.FetchAllByCategoryID(Convert.ToInt32(ddl.SelectedValue), false);
 
            ddl2.DataSource = pages;
            ddl2.DataTextField = "Title";
            ddl2.DataValueField = "ID";
            ddl2.DataBind();
 
            ddl2.Items.Insert(0, new ListItem("select", "select"));                        
        }
    }

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Accepted Solution

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ezekial316 earned 0 total points
ID: 22795539
Solved.

All down to .net life cycle and using ItemCreated instead of ItemDataBound.

Done!
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