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Load on demand using ajax combo

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ComboBox
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Rachana
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Rachana asked on 12 Jul 2012, 06:19 AM
I need to use Cascading combo boxes for that to avoid post backs i selected Load on demand Ajax Combo....
for first time selected values its working fine..when i will change item in the first combo-box the second combo box items are not get updated.my code is below

<telerik:RadComboBox ID="RadComboState" runat="server" Width="250px" Height="150px"
                                                EmptyMessage="Select a state" EnableLoadOnDemand="True" ShowMoreResultsBox="true"
                                                EnableVirtualScrolling="true" OnItemsRequested="RadComboState_ItemsRequested">
                                            </telerik:RadComboBox>
  <telerik:RadComboBox ID="RadComboInstitution" runat="server" Width="250px" Height="150px"
                                                EmptyMessage="Select an institution" EnableLoadOnDemand="True" ShowMoreResultsBox="true"
                                                EnableVirtualScrolling="true" OnItemsRequested="RadComboInstitution_ItemsRequested"
                                                OnClientItemsRequesting="GetSelectedState">
                                            </telerik:RadComboBox>
function GetSelectedState(sender, eventArgs) {
            var SelectedState;
            var combo = Telerik.Web.UI.RadComboBox.ComboBoxes[0];
            SelectedState = combo.get_value();
            var context = eventArgs.get_context();
            context["StateId"] = SelectedState;
             
        }      

protected void RadComboState_ItemsRequested(object o, RadComboBoxItemsRequestedEventArgs e)
    {
        RadComboState.Items.Clear();
        DataSet data = PoulateStates();
        if (data.Tables.Count > 0 && data.Tables[0].Rows[0][0].ToString() == "0")
        {
            int itemOffset = e.NumberOfItems;
            int endOffset = Math.Min(itemOffset + ItemsPerRequest, data.Tables[0].Rows.Count);
            e.EndOfItems = endOffset == data.Tables[0].Rows.Count;
            for (int i = itemOffset; i < endOffset; i++)
            {
                RadComboState.Items.Add(new RadComboBoxItem(data.Tables[0].Rows[i]["State_Name"].ToString(),
                                                            data.Tables[0].Rows[i]["intPkVal"].ToString()));
            }
            e.Message = GetStatusMessage(endOffset, data.Tables[0].Rows.Count);
        }
        else
        {
            RadComboBoxItem item = new RadComboBoxItem();
            item.Value = "-1";
            if (Session["COUNTRY"] != null && Session["COUNTRY"].ToString().ToUpper() == "MARSHALL ISLANDS")
                item.Text = "No Island Exists";
            else
                item.Text = "No State Exists";
            RadComboState.Items.Add(item);
        }
    }
     
    protected void RadComboInstitution_ItemsRequested(object o, RadComboBoxItemsRequestedEventArgs e)
    {
        RadComboInstitution.Items.Clear();
        DataSet Institution = new DataSet();
        
        try
        {
            string StateId = e.Context["StateId"].ToString();
            Institution = populateInstitution(StateId);
 
            if (Institution.Tables[0].Rows[0][0].ToString() == "0")
            {
                int itemOffset = e.NumberOfItems;
                int endOffset = Math.Min(itemOffset + ItemsPerRequest, Institution.Tables[0].Rows.Count);
                e.EndOfItems = endOffset == Institution.Tables[0].Rows.Count;
 
                for (int i = itemOffset; i < endOffset; i++)
                {
                    RadComboInstitution.Items.Add(
                        new RadComboBoxItem(Institution.Tables[0].Rows[i]["Institution_Name"].ToString(),
                                            Institution.Tables[0].Rows[i]["InstitutionId"].ToString()));
                }
 
                e.Message = GetStatusMessage(endOffset, Institution.Tables[0].Rows.Count);             
            }
            else
            {
                RadComboBoxItem item = new RadComboBoxItem();
                item.Value = "-1";
                item.Text = "No Institution Exists";
                RadComboInstitution.Items.Add(item);
            }
 
        }
        catch (Exception ex)
        {
        }
    }

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Princy
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answered on 12 Jul 2012, 08:10 AM
Hi Rachana,

Here is the code that I tried based on your scenario which works as expected. Refer  this demo for more.

ASPX:
<telerik:RadComboBox ID="RadComboBox1" runat="server" OnItemsRequested="RadComboBox1_ItemsRequested" OnClientSelectedIndexChanging="loadProducts">
</telerik:RadComboBox>
<telerik:RadComboBox ID="RadComboBox2" runat="server" OnItemsRequested="RadComboBox2_ItemsRequested" OnClientItemsRequested="ItemsLoaded">
</telerik:RadComboBox>

JS:
<script type="text/javascript">
 var productCombo;
 function pageLoad()
 {
  productCombo = $find("<%= RadComboBox2.ClientID %>");
 }
 function loadProducts(sender, eventArgs)
 {
  var item = eventArgs.get_item();
  productCombo.set_text("Loading...");
  if (item.get_index() > 0)
  {
   productCombo.requestItems(item.get_value(), false);
  }
  else
  {
   productCombo.set_text("");
   productCombo.clearItems();
  }
 }
 function ItemsLoaded(sender, eventArgs)
 {
   if (sender.get_items().get_count() > 0)
   {
    sender.set_text(sender.get_items().getItem(0).get_text());
    sender.get_items().getItem(0).highlight();
   }
   sender.showDropDown();
 }
</script>

C#:
protected void Page_Load(object sender, EventArgs e)
{
 if (!Page.IsPostBack)
 {
  loadCategories();
 }
 else if (!Page.IsCallback)
 {
  loadProducts(RadComboBox1.SelectedValue);
 }
}
 
protected void loadCategories()
 {
  SqlDataAdapter adapter = new SqlDataAdapter();
  adapter.SelectCommand = new SqlCommand("SELECT * FROM Customers ORDER By CompanyName", conn);
  DataTable dt = new DataTable();
  adapter.Fill(dt);
  RadComboBox1.DataTextField = "CustomerID";
  RadComboBox1.DataValueField = "CustomerID";
  RadComboBox1.DataSource = dt;
  RadComboBox1.DataBind();
  RadComboBox1.Items.Insert(0, new RadComboBoxItem("- Select.... -"));     
}
 
protected void loadProducts(string CategoryID)
 {
  SqlDataAdapter adapter = new SqlDataAdapter();
 adapter.SelectCommand = new SqlCommand("SELECT * FROM Orders WHERE CustomerID=@CustomerID ORDER By CustomerID", conn);
 adapter.SelectCommand.Parameters.AddWithValue("@CustomerID", CategoryID);
 DataTable dt = new DataTable();
 adapter.Fill(dt);
 RadComboBox2.DataTextField = "OrderID";
 RadComboBox2.DataValueField = "OrderID";
 RadComboBox2.DataSource = dt;
 RadComboBox2.DataBind();
}
 
protected void RadComboBox1_ItemsRequested(object sender, Telerik.Web.UI.RadComboBoxItemsRequestedEventArgs e)
 {
  loadCategories();
 }
protected void RadComboBox2_ItemsRequested(object sender, Telerik.Web.UI.RadComboBoxItemsRequestedEventArgs e)
 {
  loadProducts(e.Text);
 }

Thanks,
Princy.
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ComboBox
Asked by
Rachana
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Answers by
Princy
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