Group options for Asp.Net DropDownList after PostBack it is not Displaying Selected Item..

Question

User-1030697014 posted

please go to this link 

http://mpurna.blogspot.in/2012/01/group-options-for-aspnet-dropdownlist.html

after PostBack the page it selecting First ListItem Every time ..Not selected which i have selected ListItem.. 

how to display the selected item after postback also..

Thanks

Answer 1

User-707554951 posted

Hi aadikumar,

From your description, you want to group option by using ‘optgroup’ in a HTML Select Control, however, you lost selected option after a post back. If that is the case, I suggest you could use a HiddenField to save selected value. Then, resetting selected value on Button’s OnClientClick function by using jquery.

Here is an example, it works well, you could refer to it.

<script src="../../Scripts/jquery-3.1.0.min.js"></script>
    <script type="text/javascript">
        function MyFunction() {
            $("#HiddenField1").val($("#DropDownList_OptGroup1").val());
        }
        $(function () {
            var value = $("#HiddenField1").val();
            if (value.length > 0) {
                $("#DropDownList_OptGroup1").val(value);
            }
        })
</script>
<select id="DropDownList_OptGroup1" name="DropDownList_OptGroup1" >
<option value="0" selected="selected">--Select--</option>
<optgroup label="East India">
<option value="1">Bihar</option>
<option value="2">West Bengal</option>
</optgroup>
<optgroup label="North East India">
<option value="3">Assam</option>
<option value="4">Arunachal Pradesh</option>
</optgroup>
</select>       
    </div>
   <asp:HiddenField ID="HiddenField1" runat="server" Value="" />
<asp:Button ID="Button1" runat="server" OnClick="Button1_Click" OnClientClick="MyFunction()" Text="Button" />

Hope this can help you. If you have any question and confusion about the problem. Please don't hesitate to let me know.

Best regards
Cathy

 

Answer 2

User-1030697014 posted

Hi,

Thanks for your Reply and this code helps me lot.

but i am looking for server side  Code   please go through this link only Server Side code...

http://mpurna.blogspot.in/2012/01/group-options-for-aspnet-dropdownlist.html

1.  Lost selected option after a post back.

2.  how to get the Datagroup Name using C#

or is there any other control with the same functionality.

using System;

using System.Collections.Generic;

using System.ComponentModel;

using System.Text;

using System.Web;

using System.Web.UI;

using System.Web.UI.WebControls;

using System.Collections;

 

namespace DropDownList_OptGroup

{

    ///

    /// Summary description for DropDownList_OptGroup.

    ///

    [ToolboxData("<{0}:DropDownList_OptGroup runat=server>")]

    public class DropDownList_OptGroup : System.Web.UI.WebControls.DropDownList

    {

        ///

        /// The field in the datasource which provides values for groups

        ///

        [DefaultValue(""), Category("Data")]

        public virtual string DataGroupField

        {

            get

            {

                object obj = this.ViewState["DataGroupField"];

                if (obj != null)

                {

                    return (string)obj;

                }

                return string.Empty;

            }

            set

            {

                this.ViewState["DataGroupField"] = value;

            }

        }

        ///

        /// if a group doesn't has any enabled items,there is no need

        /// to render the group too

        ///

        /// ///

        private bool IsGroupHasEnabledItems(string groupName)

        {

            ListItemCollection items = this.Items;

            ListItem item;

            for (int i = 0; i < items.Count; i++)

            {

                item = items[i];

                if (item.Attributes["DataGroupField"].Equals(groupName) && item.Enabled)

                {

                    return true;

                }

            }

            return false;

        }

        ///

        /// Render this control to the output parameter specified.

        /// Based on the source code of the original DropDownList method

        ///

        /// The HTML writer to write out to

        protected override void RenderContents(HtmlTextWriter writer)

        {

            ListItemCollection items = this.Items;

            int itemCount = this.Items.Count;

            string curGroup = String.Empty;

            string itemGroup;

            bool bSelected = false;

 

            if (itemCount <= 0)

            {

                return;

            }

 

            for (int i = 0; i < itemCount; i++)

            {

                ListItem item = items[i];

                itemGroup = (string)item.Attributes["DataGroupField"];

                if (itemGroup != null && itemGroup != curGroup && IsGroupHasEnabledItems(itemGroup))

                {

                    if (curGroup != String.Empty)

                    {

                        writer.WriteEndTag("optgroup");

                        writer.WriteLine();

                    }

 

                    curGroup = itemGroup;

                    writer.WriteBeginTag("optgroup");

                    writer.WriteAttribute("label", curGroup, true);

                    writer.Write('>');

                    writer.WriteLine();

                }

                // we don't want to render disabled items

                if (item.Enabled)

                {

                    writer.WriteBeginTag("option");

                    if (item.Selected)

                    {

                        if (bSelected)

                        {

                            throw new HttpException("Cant_Multiselect_In_DropDownList");

                        }

                        bSelected = true;

                        writer.WriteAttribute("selected", "selected", false);

                    }

 

                    writer.WriteAttribute("value", item.Value, true);

                    writer.Write('>');

                    HttpUtility.HtmlEncode(item.Text, writer);

                    writer.WriteEndTag("option");

                    writer.WriteLine();

                }

            }

            if (curGroup != String.Empty)

            {

                writer.WriteEndTag("optgroup");

                writer.WriteLine();

            }

        }

 

        ///

        /// Perform data binding logic that is associated with the control

        ///

        /// An EventArgs object that contains the event data

        protected override void OnDataBinding(EventArgs e)

        {

            // Call base method to bind data

            base.OnDataBinding(e);

 

            if (this.DataGroupField == String.Empty)

            {

                return;

            }

            // For each Item add the attribute "DataGroupField" with value from the datasource

            IEnumerable dataSource = GetResolvedDataSource(this.DataSource, this.DataMember);

            if (dataSource != null)

            {

                ListItemCollection items = this.Items;

                int i = 0;

 

                string groupField = this.DataGroupField;

                foreach (object obj in dataSource)

                {

                    string groupFieldValue = DataBinder.GetPropertyValue(obj, groupField, null);

                    ListItem item = items[i];

                    item.Attributes.Add("DataGroupField", groupFieldValue);

                    i++;

                }

            }

 

        }

 

        ///

        /// This is copy of the internal ListControl method

        ///

        /// /// ///

        private IEnumerable GetResolvedDataSource(object dataSource, string dataMember)

        {

            if (dataSource != null)

            {

                IListSource source1 = dataSource as IListSource;

                if (source1 != null)

                {

                    IList list1 = source1.GetList();

                    if (!source1.ContainsListCollection)

                    {

                        return list1;

                    }

                    if ((list1 != null) && (list1 is ITypedList))

                    {

                        ITypedList list2 = (ITypedList)list1;

                        PropertyDescriptorCollection collection1 = list2.GetItemProperties(new PropertyDescriptor[0]);

                        if ((collection1 == null) || (collection1.Count == 0))

                        {

                            throw new HttpException("ListSource_Without_DataMembers");

                        }

                        PropertyDescriptor descriptor1 = null;

                        if ((dataMember == null) || (dataMember.Length == 0))

                        {

                            descriptor1 = collection1[0];

                        }

                        else

                        {

                            descriptor1 = collection1.Find(dataMember, true);

                        }

                        if (descriptor1 != null)

                        {

                            object obj1 = list1[0];

                            object obj2 = descriptor1.GetValue(obj1);

                            if ((obj2 != null) && (obj2 is IEnumerable))

                            {

                                return (IEnumerable)obj2;

                            }

                        }

                        throw new HttpException("ListSource_Missing_DataMember");

                    }

                }

                if (dataSource is IEnumerable)

                {

                    return (IEnumerable)dataSource;

                }

            }

            return null;

        }

        #region Internal behaviour

        /// Saves the state of the view.

        ///

        protected override object SaveViewState()

        {

            // Create an object array with one element for the CheckBoxList's'

            // ViewState contents, and one element for each ListItem in skmCheckBoxList

            object[] state = new object[this.Items.Count + 1];

 

            object baseState = base.SaveViewState();

            state[0] = baseState;

 

            // Now, see if we even need to save the view state

            bool itemHasAttributes = false;

            for (int i = 0; i < this.Items.Count; i++)

            {

                if (this.Items[i].Attributes.Count > 0)

                {

                    itemHasAttributes = true;

 

                    // Create an array of the item's Attribute's keys and values

                    object[] attribKV = new object[this.Items[i].Attributes.Count * 2];

                    int k = 0;

                    foreach (string key in this.Items[i].Attributes.Keys)

                    {

                        attribKV[k++] = key;

                        attribKV[k++] = this.Items[i].Attributes[key];

                    }

 

                    state[i + 1] = attribKV;

                }

            }

 

            // return either baseState or state, depending on whether or not

            // any ListItems had attributes

            if (itemHasAttributes)

                return state;

            else

                return baseState;

        }

 

        ///

        /// Loads the state of the view.

        ///

        /// State of the saved.

        protected override void LoadViewState(object savedState)

        {

            if (savedState == null) return;

 

            // see if savedState is an object or object array

            if (savedState is object[])

            {

                // we have an array of items with attributes

                object[] state = (object[])savedState;

                base.LoadViewState(state[0]);   // load the base state

 

                for (int i = 1; i < state.Length; i++)

                {

                    if (state[i] != null)

                    {

                        // Load back in the attributes

                        object[] attribKV = (object[])state[i];

                        for (int k = 0; k < attribKV.Length; k += 2)

                            this.Items[i - 1].Attributes.Add(attribKV[k].ToString(),

                                                           attribKV[k + 1].ToString());

                    }

                }

            }

            else

                // we have just the base state

                base.LoadViewState(savedState);

        }

        #endregion

    }

}

 

 

5) Rebuild the solution

 

6) Open the solution of your website


7) Toolbox-> Right Click on it and select "Add tab", then write the name of the tab as Extended Controls


8) Right-click on that tab then select "choose items",then from ".Net FrameWork Components" click "Browse", 
then point to the dll that was created by our class library..it's name is "DropDownList_OptGroup.dll".then click OK,then OK for the other dialog, you will notice that our dropdownlist control has been added to the toolbox


9) drag-n-drop DropDownList_OptGroup control


Usage:

Countryid   Country_name        Region

----------  ------------------  ------------------

1           Bihar               East India

2           West Bengal         East India

3           Assam               North East India

4           Arunachal Pradesh   North East India

5           Rajasthan           North India

6           Punjab              North India

7           Jammu and Kashmir   North India

8           Andhra Pradesh      South India

9           Tamilnadu           South India

10          Karnataka           South India

11          Kerala              South India

12          Gujarat             West India

13          Maharashtra         West India

 

    DataView regionview = ds.Tables[0].DefaultView;

    regionview.Sort = "region asc";

    DropDownList_OptGroup1.DataSource = regionview;

    DropDownList_OptGroup1.DataTextField = "country_name";

    DropDownList_OptGroup1.DataValueField = "countryid";

    DropDownList_OptGroup1.DataGroupField = "region";

    DropDownList_OptGroup1.DataBind();

    ListItem li = new ListItem("--Select--", "0");

    li.Attributes.Add("DataGroupField", "");

    DropDownList_OptGroup1.Items.Insert(0, li);

Thanks.

 

Answer 3

User-707554951 posted

Hi aadikumar,

1.  Lost selected option after a post back.

For your first question, I supposed that you bind custom DDL in every time page load rather than in the first page load. So, I suggest you could to add if (!IsPostBack) in your page load event.

2.  how to get the Datagroup Name using C#

For you second question, I suggest you could use Attributes Property of ListItem to get DataGrop Name
The code below is a sample you could refer to it:

  <cc1:DropDownList_OptGroup ID="DropDownList_OptGroup1" runat="server" AutoPostBack="true" OnSelectedIndexChanged="DropDownList_OptGroup1_SelectedIndexChanged">
        </cc1:DropDownList_OptGroup>
        <asp:Button ID="Button1" runat="server" Text="Button" />

CodeBehind:

protected void Page_Load(object sender, EventArgs e)
        {    if (!IsPostBack)
            {
                string constr = ConfigurationManager.ConnectionStrings["ConnectionString"].ConnectionString;
                using (SqlConnection con = new SqlConnection(constr))
                {
                    using (SqlCommand cmd = new SqlCommand("select * from CustomTable"))
                    {
                        using (SqlDataAdapter sda = new SqlDataAdapter())
                        {
                            cmd.Connection = con;
                            sda.SelectCommand = cmd;
                            using (DataSet ds = new DataSet())
                            {
                                sda.Fill(ds);
                                DataView regionview = ds.Tables[0].DefaultView;
                                regionview.Sort = "Regin asc";
                                DropDownList_OptGroup1.DataSource = regionview;
                                DropDownList_OptGroup1.DataTextField = "Name";
                                DropDownList_OptGroup1.DataValueField = "Id";
                                DropDownList_OptGroup1.DataGroupField = "Regin";
                                DropDownList_OptGroup1.DataBind();
                                ListItem li = new ListItem("--Select--", "0");
                                li.Attributes.Add("DataGroupField", "");
                                DropDownList_OptGroup1.Items.Insert(0, li);
                                // string s=DropDownList_OptGroup1.DataGroupField.ToString();
                                string s = DropDownList_OptGroup1.SelectedItem.Attributes["DataGroupField"];
                            }
                        }
                    }
                }
            }     
        }

        protected void DropDownList_OptGroup1_SelectedIndexChanged(object sender, EventArgs e)
        {    //get datagroup name
            string s = DropDownList_OptGroup1.SelectedItem.Attributes["DataGroupField"];
        }

Hope this can help you. If you have any question and confusion about the problem. Please don't hesitate to let me know.
Best regards
Cathy