ADF tutorials
ADFTutorials_CSharp\UsingCommonAPI\Default.aspx.cs
// Copyright 2011 ESRI
// 
// All rights reserved under the copyright laws of the United States
// and applicable international laws, treaties, and conventions.
// 
// You may freely redistribute and use this sample code, with or
// without modification, provided you include the original copyright
// notice and use restrictions.
// 
// See the use restrictions.
// 

using System;
using System.Data;
using System.Configuration;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Web.UI.HtmlControls;

public partial class _Default : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs eventArgs)
    {
        // Store the TaskResults control in session for use by the custom tool
        Session["TaskResultsControl"] = TaskResults1;

        // Add a handler for the resource drop-down's SelectedIndexChanged event
        DropDownList1.SelectedIndexChanged += new
        EventHandler(DropDownList1_SelectedIndexChanged);
    }

    void DropDownList1_SelectedIndexChanged(object sender, EventArgs eventArgs)
    {
        // Clear the layers drop-down
        DropDownList2.Items.Clear();

        // Get the names of queryable layers for the selected resource and add them
        // to the layers drop-down
        string[] layerNames = GetQueryableLayerNames(DropDownList1.SelectedItem.Text);
        for (int i = 0; i < layerNames.Length; i++)
            DropDownList2.Items.Add(layerNames[i]);
    }


    protected void Page_PreRender(object sender, EventArgs eventArgs)
    {
        if (DropDownList1.Items.Count == 0)
        {
            // Add resource names to the resource drop-down list
            foreach (ESRI.ArcGIS.ADF.Web.UI.WebControls.MapResourceItem
            mapResourceItem in MapResourceManager1.ResourceItems)
                DropDownList1.Items.Add(mapResourceItem.Resource.Name);

            // Get the names of queryable layers for the selected resource and add them
            // to the layers drop-down
            string[] layerNames = GetQueryableLayerNames(DropDownList1.SelectedItem.Text);
            for (int i = 0; i < layerNames.Length; i++)
                DropDownList2.Items.Add(layerNames[i]);
        }
    }

    private string[] GetQueryableLayerNames(string resourceName)
    {
        // Get a reference to the resource
        ESRI.ArcGIS.ADF.Web.DataSources.IMapFunctionality commonMapFunctionality =
            Map1.GetFunctionality(resourceName);
        ESRI.ArcGIS.ADF.Web.DataSources.IGISResource gisResource = commonMapFunctionality.Resource;

        // Create a query functionality to use in querying the resource
        ESRI.ArcGIS.ADF.Web.DataSources.IQueryFunctionality commonQueryFunctionality =
            (ESRI.ArcGIS.ADF.Web.DataSources.IQueryFunctionality)
            gisResource.CreateFunctionality(
            typeof(ESRI.ArcGIS.ADF.Web.DataSources.IQueryFunctionality), null);

        // Get the resource's queryable layers
        string[] layerIDs = null;
        string[] layerNames = null;
        commonQueryFunctionality.GetQueryableLayers(null, out layerIDs, out layerNames);

        return layerNames;
    }


}