Implement Show All and Hide All Button in Nested GridView with Paging in ASP.Net

Here I have created sample that full-fill your requirement.

I hope this will help you out.

HTML

<div>
    <script type="text/javascript" src="http://ajax.googleapis.com/ajax/libs/jquery/1.8.3/jquery.min.js"></script>
    <script type="text/javascript">
        $(function () {
            $("[id*=imgOrdersShow]").each(function () {
                if ($(this)[0].src.indexOf("minus") != -1) {
                    $(this).closest("tr").after("<tr><td></td><td colspan = '999'>" + $(this).next().html() + "</td></tr>");
                    $(this).next().remove();
                }
            });
            $("[id*=imgProductsShow]").each(function () {
                if ($(this)[0].src.indexOf("minus") != -1) {
                    $(this).closest("tr").after("<tr><td></td><td colspan = '999'>" + $(this).next().html() + "</td></tr>");
                    $(this).next().remove();
                }
            });
        });
    </script>
    <asp:ImageButton ID="imgShowAllGrid" ImageUrl="~/images/plus.png" OnClick="Show_Hide_AllGrid"
        CommandArgument="ShowAll" runat="server" Style="background-color: Red" />
    <br />
    <br />
    <asp:GridView ID="gvCustomers" runat="server" AutoGenerateColumns="false" CssClass="Grid"
        DataKeyNames="CustomerID">
        <Columns>
            <asp:TemplateField>
                <ItemTemplate>
                    <asp:ImageButton ID="imgOrdersShow" runat="server" OnClick="Show_Hide_OrdersGrid"
                        ImageUrl="~/images/plus.png" CommandArgument="Show" />
                    <asp:Panel ID="pnlOrders" runat="server" Visible="false" Style="position: relative">
                        <asp:GridView ID="gvOrders" runat="server" AutoGenerateColumns="false" PageSize="5"
                            AllowPaging="true" OnPageIndexChanging="OnOrdersGrid_PageIndexChanging" CssClass="ChildGrid"
                            DataKeyNames="OrderId">
                            <Columns>
                                <asp:TemplateField>
                                    <ItemTemplate>
                                        <asp:ImageButton ID="imgProductsShow" runat="server" OnClick="Show_Hide_ProductsGrid"
                                            ImageUrl="~/images/plus.png" CommandArgument="Show" />
                                        <asp:Panel ID="pnlProducts" runat="server" Visible="false" Style="position: relative">
                                            <asp:GridView ID="gvProducts" runat="server" AutoGenerateColumns="false" PageSize="2"
                                                AllowPaging="true" OnPageIndexChanging="OnProductsGrid_PageIndexChanging" CssClass="Nested_ChildGrid">
                                                <Columns>
                                                    <asp:BoundField ItemStyle-Width="150px" DataField="ProductId" HeaderText="Product Id" />
                                                    <asp:BoundField ItemStyle-Width="150px" DataField="ProductName" HeaderText="Product Name" />
                                                </Columns>
                                            </asp:GridView>
                                        </asp:Panel>
                                    </ItemTemplate>
                                </asp:TemplateField>
                                <asp:BoundField ItemStyle-Width="150px" DataField="OrderId" HeaderText="Order Id" />
                                <asp:BoundField ItemStyle-Width="150px" DataField="OrderDate" HeaderText="Date" />
                            </Columns>
                        </asp:GridView>
                    </asp:Panel>
                </ItemTemplate>
            </asp:TemplateField>
            <asp:BoundField ItemStyle-Width="150px" DataField="ContactName" HeaderText="Contact Name" />
            <asp:BoundField ItemStyle-Width="150px" DataField="City" HeaderText="City" />
        </Columns>
    </asp:GridView>
</div>

Code

protected void Page_Load(object sender, EventArgs e)
{
    if (!IsPostBack)
    {
        gvCustomers.DataSource = GetData("select top 10 * from Customers");
        gvCustomers.DataBind();
    }
}

private static DataTable GetData(string query)
{
    string constr = ConfigurationManager.ConnectionStrings["constr"].ConnectionString;
    using (SqlConnection con = new SqlConnection(constr))
    {
        using (SqlCommand cmd = new SqlCommand())
        {
            cmd.CommandText = query;
            using (SqlDataAdapter sda = new SqlDataAdapter())
            {
                cmd.Connection = con;
                sda.SelectCommand = cmd;
                using (DataSet ds = new DataSet())
                {
                    DataTable dt = new DataTable();
                    sda.Fill(dt);
                    return dt;
                }
            }
        }
    }
}

protected void Show_Hide_OrdersGrid(object sender, EventArgs e)
{
    ImageButton imgOrderShowHide = (sender as ImageButton);
    GridViewRow row = (imgOrderShowHide.NamingContainer as GridViewRow);
    if (imgOrderShowHide.CommandArgument == "Show")
    {
        row.FindControl("pnlOrders").Visible = true;
        imgOrderShowHide.CommandArgument = "Hide";
        imgOrderShowHide.ImageUrl = "~/images/minus.png";
        string customerId = gvCustomers.DataKeys[row.RowIndex].Value.ToString();
        GridView gvOrders = row.FindControl("gvOrders") as GridView;
        BindOrders(customerId, gvOrders);
    }
    else
    {
        row.FindControl("pnlOrders").Visible = false;
        imgOrderShowHide.CommandArgument = "Show";
        imgOrderShowHide.ImageUrl = "~/images/plus.png";
    }
}

protected void Show_Hide_AllGrid(object sender, EventArgs e)
{
    ImageButton imgAllOrdersShowHide = (sender as ImageButton);
    if (imgAllOrdersShowHide.CommandArgument == "ShowAll")
    {
        foreach (GridViewRow row in gvCustomers.Rows)
        {
            ImageButton imgCustomerShowHide = (ImageButton)row.FindControl("imgOrdersShow");
            row.FindControl("pnlOrders").Visible = true;
            imgCustomerShowHide.CommandArgument = "Hide";
            imgCustomerShowHide.ImageUrl = "~/images/minus.png";
            string customerId = gvCustomers.DataKeys[row.RowIndex].Value.ToString();
            GridView gvOrders = row.FindControl("gvOrders") as GridView;
            BindOrders(customerId, gvOrders);
            foreach (GridViewRow orderRow in gvOrders.Rows)
            {
                GridView gvProducts = (GridView)(orderRow.FindControl("gvProducts"));
                ImageButton imgProductShowHide = (ImageButton)orderRow.FindControl("imgProductsShow");
                orderRow.FindControl("pnlProducts").Visible = true;
                imgProductShowHide.CommandArgument = "Hide";
                imgProductShowHide.ImageUrl = "~/images/minus.png";
                int orderId = Convert.ToInt32((orderRow.NamingContainer as GridView).DataKeys[orderRow.RowIndex].Value);
                BindProducts(orderId, gvProducts);
            }
        }
        imgAllOrdersShowHide.CommandArgument = "HideAll";
        imgAllOrdersShowHide.ImageUrl = "~/images/minus.png";

    }
    else
    {
        foreach (GridViewRow row in gvCustomers.Rows)
        {
            ImageButton imgCustomerShowHide = (ImageButton)row.FindControl("imgOrdersShow");
            row.FindControl("pnlOrders").Visible = false;
            imgCustomerShowHide.CommandArgument = "Show";
            imgCustomerShowHide.ImageUrl = "~/images/plus.png";
        }
        imgAllOrdersShowHide.CommandArgument = "ShowAll";
        imgAllOrdersShowHide.ImageUrl = "~/images/plus.png";
    }
}

private void BindOrders(string customerId, GridView gvOrders)
{
    gvOrders.ToolTip = customerId;
    gvOrders.DataSource = GetData(string.Format("select * from Orders where CustomerId='{0}'", customerId));
    gvOrders.DataBind();
}

protected void OnOrdersGrid_PageIndexChanging(object sender, GridViewPageEventArgs e)
{
    GridView gvOrders = (sender as GridView);
    gvOrders.PageIndex = e.NewPageIndex;
    BindOrders(gvOrders.ToolTip, gvOrders);
}

protected void Show_Hide_ProductsGrid(object sender, EventArgs e)
{
    ImageButton imgProductShowHide = (sender as ImageButton);
    GridViewRow row = (imgProductShowHide.NamingContainer as GridViewRow);
    if (imgProductShowHide.CommandArgument == "Show")
    {
        row.FindControl("pnlProducts").Visible = true;
        imgProductShowHide.CommandArgument = "Hide";
        imgProductShowHide.ImageUrl = "~/images/minus.png";
        int orderId = Convert.ToInt32((row.NamingContainer as GridView).DataKeys[row.RowIndex].Value);
        GridView gvProducts = row.FindControl("gvProducts") as GridView;
        BindProducts(orderId, gvProducts);
    }
    else
    {
        row.FindControl("pnlProducts").Visible = false;
        imgProductShowHide.CommandArgument = "Show";
        imgProductShowHide.ImageUrl = "~/images/plus.png";
    }
}

private void BindProducts(int orderId, GridView gvProducts)
{
    gvProducts.ToolTip = orderId.ToString();
    gvProducts.DataSource = GetData(string.Format("SELECT ProductId, ProductName FROM Products WHERE ProductId IN (SELECT ProductId FROM [Order Details] WHERE OrderId = '{0}')", orderId));
    gvProducts.DataBind();
}

protected void OnProductsGrid_PageIndexChanging(object sender, GridViewPageEventArgs e)
{
    GridView gvProducts = (sender as GridView);
    gvProducts.PageIndex = e.NewPageIndex;
    BindProducts(int.Parse(gvProducts.ToolTip), gvProducts);
}

Screenshot