Check multiple checkbox checked in multiselect DropDownList in GridView edit event in ASP.Net

Hi, veenahosur

I have created sample code which fullfill your requirement.

HTML

<form id="form1" runat="server">
<div>
    <asp:GridView ID="GridView1" runat="server" AutoGenerateColumns="false" OnRowEditing="OnRowEditing">
        <Columns>
            <asp:TemplateField HeaderText="Name" ItemStyle-Width="150">
                <ItemTemplate>
                    <asp:Label ID="lblName" Text='<%# Eval("Name") %>' runat="server" />
                </ItemTemplate>
                <EditItemTemplate>
                    <asp:TextBox ID="txtName" runat="server" Text='<%# Eval("Name") %>' />
                </EditItemTemplate>
            </asp:TemplateField>
            <asp:TemplateField HeaderText="Country" ItemStyle-Width="150">
                <ItemTemplate>
                    <asp:Label ID="lblcountry" Text='<%# Eval("Country") %>' runat="server" />
                </ItemTemplate>
                <EditItemTemplate>
                    <asp:ListBox ID="ddlCountries" runat="server" SelectionMode="Multiple">
                        <asp:ListItem Text="United States" Value="United States" />
                        <asp:ListItem Text="India" Value="India" />
                        <asp:ListItem Text="France" Value="France" />
                        <asp:ListItem Text="Russia" Value="Russia" />
                    </asp:ListBox>
                </EditItemTemplate>
            </asp:TemplateField>
            <asp:TemplateField>
                <ItemTemplate>
                    <asp:LinkButton ID="LinkButton1" Text="Edit" runat="server" CommandName="Edit" />
                </ItemTemplate>
                <EditItemTemplate>
                    <asp:LinkButton ID="LinkButton2" Text="Update" runat="server" OnClick="OnUpdate"
                        OnClientClick="return Validate(this)" />
                    <asp:LinkButton ID="LinkButton3" Text="Cancel" runat="server" OnClick="OnCancel" />
                </EditItemTemplate>
            </asp:TemplateField>
        </Columns>
    </asp:GridView>
</div>
<div>
    <script type="text/javascript" src="http://ajax.googleapis.com/ajax/libs/jquery/1.8.3/jquery.min.js"></script>
    <link href="http://cdnjs.cloudflare.com/ajax/libs/twitter-bootstrap/3.0.3/css/bootstrap.min.css"
        rel="stylesheet" type="text/css" />
    <script type="text/javascript" src="http://cdnjs.cloudflare.com/ajax/libs/twitter-bootstrap/3.0.3/js/bootstrap.min.js"></script>
    <link href="http://cdn.rawgit.com/davidstutz/bootstrap-multiselect/master/dist/css/bootstrap-multiselect.css"
        rel="stylesheet" type="text/css" />
    <script src="http://cdn.rawgit.com/davidstutz/bootstrap-multiselect/master/dist/js/bootstrap-multiselect.js"
        type="text/javascript"></script>
    <script type="text/javascript">
        $(function () {
            $('[id*=ddlCountries]').multiselect({
                includeSelectAllOption: true
            });
        });
    </script>
</div>
</form>

C#

protected void Page_Load(object sender, EventArgs e)
{
    if (!this.IsPostBack)
    {
        DataTable dt = new DataTable();
        dt.Columns.AddRange(new DataColumn[3] { new DataColumn("Id"), new DataColumn("Name"), new DataColumn("Country") });
        dt.Rows.Add(1, "John Hammond", "United States");
        dt.Rows.Add(2, "Mudassar Khan", "India");
        dt.Rows.Add(3, "Suzanne Mathews", "France");
        dt.Rows.Add(4, "Robert Schidner", "Russia");
        ViewState["dt"] = dt;
        this.BindGrid();
    }
}

private void BindGrid()
{
    DataTable dtbind = ViewState["dt"] as DataTable;
    GridView1.DataSource = dtbind;
    GridView1.DataBind();
}

protected void OnRowEditing(object sender, GridViewEditEventArgs e)
{
    GridView1.EditIndex = e.NewEditIndex;
    string country = (GridView1.Rows[e.NewEditIndex].FindControl("lblcountry") as Label).Text;
    List<string> SelectedNamed = country.Split(',').Reverse().ToList();
    this.BindGrid();
    ListBox onEdit = (ListBox)(GridView1.Rows[e.NewEditIndex].FindControl("ddlCountries"));
    for (int i = 0; i < (SelectedNamed).Count; i++)
    {
        foreach (ListItem item in onEdit.Items)
        {
            if (item.ToString() == Convert.ToString(SelectedNamed[i]))
            {
                item.Selected = true;
            }
        }
    }
}

protected void OnUpdate(object sender, EventArgs e)
{
    GridViewRow row = (sender as LinkButton).NamingContainer as GridViewRow;
    string name = (row.FindControl("txtName") as TextBox).Text;
    string countryAdd = string.Empty;
    ListBox cblProject = (ListBox)(row.FindControl("ddlCountries"));
    foreach (ListItem item in cblProject.Items)
    {
        if (item.Selected)
        {
            countryAdd += item.Text + ",";
        }
    }
    countryAdd.Replace(",", " ");
    DataTable dt = ViewState["dt"] as DataTable;
    dt.Rows[row.RowIndex]["Name"] = name;
    dt.Rows[row.RowIndex]["Country"] = countryAdd.Remove(countryAdd.Length - 1);
    ViewState["dt"] = dt;
    GridView1.EditIndex = -1;
    this.BindGrid();
}

protected void OnCancel(object sender, EventArgs e)
{
    GridView1.EditIndex = -1;
    this.BindGrid();
}

Screenshot