[Solved] ViewState loses values on ASP.Net GridView CheckBox checked (selected)

Hi tanweeruddinb...,

Kindly find below sample.

Database

I have made use of the following table Customers with the schema as follows.

I have already inserted few records in the table.

You can download the database table SQL by clicking the download link below.

Download SQL file

HTML

<asp:GridView runat="server" ID="gvCustomers" AutoGenerateColumns="false">
    <Columns>
        <asp:TemplateField>
            <ItemTemplate>
                <asp:CheckBox runat="server" AutoPostBack="true" OnCheckedChanged="OnCheckedChanged" />
            </ItemTemplate>
        </asp:TemplateField>
        <asp:TemplateField HeaderText="ID">
            <ItemTemplate>
                <asp:Label ID="lblstu_id" Text='<%#Eval("CustomerId") %>' runat="server" />
            </ItemTemplate>
        </asp:TemplateField>
        <asp:BoundField DataField="Name" HeaderText="Name" />
    </Columns>
</asp:GridView>
<hr />
<asp:GridView runat="server" ID="gvStudents"></asp:GridView>

Namespaces

C#

using System.Configuration;
using System.Data;
using System.Data.SqlClient;

VB.Net

Imports System.Configuration
Imports System.Data
Imports System.Data.SqlClient

Code

C#

protected void Page_Load(object sender, EventArgs e)
{
    if (!this.IsPostBack)
    {
        this.BindGrid();
    }
}

private void BindGrid()
{
    string conn = ConfigurationManager.ConnectionStrings["constr"].ConnectionString;
    using (SqlConnection con = new SqlConnection(conn))
    {
        using (SqlCommand cmd = new SqlCommand("SELECT CustomerId, Name, Country FROM Customers", con))
        {
            using (SqlDataAdapter sda = new SqlDataAdapter(cmd))
            {
                using (DataTable dt = new DataTable())
                {
                    sda.Fill(dt);
                    gvCustomers.DataSource = dt;
                    gvCustomers.DataBind();
                }
            }
        }
    }
}

public List<tblstudent> students_
{
    get
    {
        if (ViewState["List_Student"] == null)
        {
            return new List<tblstudent>();
        }
        else
        {
            return (List<tblstudent>)ViewState["List_Student"];
        }
    }
    set { ViewState["List_Student"] = value; }
}

[Serializable]
public class tblstudent
{
    public string Stu_id { get; set; }
}

protected void OnCheckedChanged(object sender, EventArgs args)
{
    CheckBox chkBox = sender as CheckBox;
    GridViewRow item = (GridViewRow)(sender as Control).NamingContainer;
    Label lblstu_id = (Label)item.FindControl("lblstu_id");
    switch (chkBox.Checked)
    {
        case true:
            List<tblstudent> students = students_;
            students.Add(new tblstudent { Stu_id = lblstu_id.Text });
            students_ = students;
            break;
    }

    gvStudents.DataSource = students_;
    gvStudents.DataBind();
}

VB.Net

Protected Sub Page_Load(ByVal sender As Object, ByVal e As EventArgs) Handles Me.Load
    If Not Me.IsPostBack Then
        Me.BindGrid()
    End If
End Sub

Private Sub BindGrid()
    Dim conn As String = ConfigurationManager.ConnectionStrings("constr").ConnectionString
    Using con As SqlConnection = New SqlConnection(conn)
        Using cmd As SqlCommand = New SqlCommand("SELECT CustomerId, Name, Country FROM Customers", con)
            Using sda As SqlDataAdapter = New SqlDataAdapter(cmd)
                Using dt As DataTable = New DataTable()
                    sda.Fill(dt)
                    gvCustomers.DataSource = dt
                    gvCustomers.DataBind()
                End Using
            End Using
        End Using
    End Using
End Sub

Public Property students_ As List(Of tblstudent)
    Get
        If ViewState("List_Student") Is Nothing Then
            Return New List(Of tblstudent)()
        Else
            Return CType(ViewState("List_Student"), List(Of tblstudent))
        End If
    End Get
    Set(ByVal value As List(Of tblstudent))
        ViewState("List_Student") = value
    End Set
End Property

<Serializable>
Public Class tblstudent
    Public Property Stu_id As String
End Class

Protected Sub OnCheckedChanged(ByVal sender As Object, ByVal args As EventArgs)
    Dim chkBox As CheckBox = TryCast(sender, CheckBox)
    Dim item As GridViewRow = CType((TryCast(sender, Control)).NamingContainer, GridViewRow)
    Dim lblstu_id As Label = CType(item.FindControl("lblstu_id"), Label)

    Select Case chkBox.Checked
        Case True
            Dim students As List(Of tblstudent) = students_
            students.Add(New tblstudent With {
                .Stu_id = lblstu_id.Text
            })
            students_ = students
    End Select

    gvStudents.DataSource = students_
    gvStudents.DataBind()
End Sub

Screenshot