working with a CheckBox in a DataGrid in WebForms

I'm using VB and ASP.NET Web Forms.

On my page i'm binding a DataGrid to a Sql Server Stored procedure.

Yest, I know GridView is the newer ASP.NET grid.
This is a model based on a old legacy web application.
That's why I need to use DataGrid.

The sql server table I'm using is a copy of the Employees table from the Northwind database.

This is the script to create the table:

USE [Northwind]
GO

SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO
CREATE TABLE [dbo].[NWEmployees](
	[EmployeeID] [int] NOT NULL,
	[LastName] [nvarchar](20) NOT NULL,
	[FirstName] [nvarchar](10) NOT NULL,
	[Title] [nvarchar](30) NULL,
	[TitleOfCourtesy] [nvarchar](25) NULL,
	[BirthDate] [datetime] NULL,
	[HireDate] [datetime] NULL,
	[Address] [nvarchar](60) NULL,
	[City] [nvarchar](15) NULL,
	[Region] [nvarchar](15) NULL,
	[PostalCode] [int] NULL,
	[Country] [nvarchar](15) NULL,
 CONSTRAINT [PK_Employees_NWEmployees] PRIMARY KEY CLUSTERED 
(
	[EmployeeID] ASC
)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY]
) ON [PRIMARY]

GO
INSERT [dbo].[NWEmployees] ([EmployeeID], [LastName], [FirstName], [Title], [TitleOfCourtesy], [BirthDate], [HireDate], [Address], [City], [Region], [PostalCode], [Country]) VALUES (1, N'Davolio', N'Nancy', N'Sales Representative', N'Ms.', CAST(N'1948-12-08T00:00:00.000' AS DateTime), CAST(N'1992-05-01T00:00:00.000' AS DateTime), N'507 - 20th Ave. E.
Apt. 2A', N'Seattle', N'WA', 98122, N'USA')
INSERT [dbo].[NWEmployees] ([EmployeeID], [LastName], [FirstName], [Title], [TitleOfCourtesy], [BirthDate], [HireDate], [Address], [City], [Region], [PostalCode], [Country]) VALUES (2, N'Fuller', N'Andrew', N'Vice President, Sales', N'Dr.', CAST(N'1952-02-19T00:00:00.000' AS DateTime), CAST(N'1992-08-14T00:00:00.000' AS DateTime), N'908 W. Capital Way', N'Tacoma', N'WA', 98401, N'USA')
INSERT [dbo].[NWEmployees] ([EmployeeID], [LastName], [FirstName], [Title], [TitleOfCourtesy], [BirthDate], [HireDate], [Address], [City], [Region], [PostalCode], [Country]) VALUES (3, N'Leverling', N'Janet', N'Sales Representative', N'Ms.', CAST(N'1963-08-30T00:00:00.000' AS DateTime), CAST(N'1992-04-01T00:00:00.000' AS DateTime), N'722 Moss Bay Blvd.', N'Kirkland', N'WA', 98033, N'USA')
INSERT [dbo].[NWEmployees] ([EmployeeID], [LastName], [FirstName], [Title], [TitleOfCourtesy], [BirthDate], [HireDate], [Address], [City], [Region], [PostalCode], [Country]) VALUES (4, N'Peacock', N'Margaret', N'Sales Representative', N'Mrs.', CAST(N'1937-09-19T00:00:00.000' AS DateTime), CAST(N'1993-05-03T00:00:00.000' AS DateTime), N'4110 Old Redmond Rd.', N'Redmond', N'WA', 98052, N'USA')
INSERT [dbo].[NWEmployees] ([EmployeeID], [LastName], [FirstName], [Title], [TitleOfCourtesy], [BirthDate], [HireDate], [Address], [City], [Region], [PostalCode], [Country]) VALUES (5, N'Buchanan', N'Steven', N'Sales Manager', N'Mr.', CAST(N'1955-03-04T00:00:00.000' AS DateTime), CAST(N'1993-10-17T00:00:00.000' AS DateTime), N'14 Garrett Hill', N'London', NULL, 95624, N'UK')
INSERT [dbo].[NWEmployees] ([EmployeeID], [LastName], [FirstName], [Title], [TitleOfCourtesy], [BirthDate], [HireDate], [Address], [City], [Region], [PostalCode], [Country]) VALUES (6, N'Suyama', N'Michael', N'Sales Representative', N'Mr.', CAST(N'1963-07-02T00:00:00.000' AS DateTime), CAST(N'1993-10-17T00:00:00.000' AS DateTime), N'Coventry House
Miner Rd.', N'London', NULL, 93722, N'UK')
INSERT [dbo].[NWEmployees] ([EmployeeID], [LastName], [FirstName], [Title], [TitleOfCourtesy], [BirthDate], [HireDate], [Address], [City], [Region], [PostalCode], [Country]) VALUES (7, N'King', N'Robert', N'Sales Representative', N'Mr.', CAST(N'1960-05-29T00:00:00.000' AS DateTime), CAST(N'1994-01-02T00:00:00.000' AS DateTime), N'Edgeham Hollow
Winchester Way', N'London', NULL, 45648, N'UK')
INSERT [dbo].[NWEmployees] ([EmployeeID], [LastName], [FirstName], [Title], [TitleOfCourtesy], [BirthDate], [HireDate], [Address], [City], [Region], [PostalCode], [Country]) VALUES (8, N'Callahan', N'Laura', N'Inside Sales Coordinator', N'Ms.', CAST(N'1958-01-09T00:00:00.000' AS DateTime), CAST(N'1994-03-05T00:00:00.000' AS DateTime), N'4726 - 11th Ave. N.E.', N'Seattle', N'WA', 98105, N'USA')
INSERT [dbo].[NWEmployees] ([EmployeeID], [LastName], [FirstName], [Title], [TitleOfCourtesy], [BirthDate], [HireDate], [Address], [City], [Region], [PostalCode], [Country]) VALUES (9, N'Dodsworth', N'Anne', N'Sales Representative', N'Ms.', CAST(N'1966-01-27T00:00:00.000' AS DateTime), CAST(N'1994-11-15T00:00:00.000' AS DateTime), N'7 Houndstooth Rd.', N'London', NULL, 98751, N'UK')
INSERT [dbo].[NWEmployees] ([EmployeeID], [LastName], [FirstName], [Title], [TitleOfCourtesy], [BirthDate], [HireDate], [Address], [City], [Region], [PostalCode], [Country]) VALUES (10, N'Duck', N'Daffy', N'Actor', NULL, NULL, NULL, NULL, NULL, NULL, 90210, NULL)
INSERT [dbo].[NWEmployees] ([EmployeeID], [LastName], [FirstName], [Title], [TitleOfCourtesy], [BirthDate], [HireDate], [Address], [City], [Region], [PostalCode], [Country]) VALUES (11, N'Duck', N'Donald', N'Disney Actor', NULL, NULL, NULL, NULL, NULL, NULL, 90211, NULL)

This is the script for the stored procedure:

USE [Northwind]
GO

SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO

CREATE PROCEDURE [dbo].[NWEmployees_Get]
AS

SELECT [EmployeeID]
      ,[LastName]
      ,[FirstName]
      ,[Title]
      ,[BirthDate]
      ,[HireDate]
      ,[Address]
      ,[City]
      ,[Region]
      ,[PostalCode]
      ,[Country]
FROM [Northwind].[dbo].[NWEmployees]


GO

When I run my page it runs fine it looks like this:

Notice I have 2 buttons above the DataGrid.

If I click the Check Header CheckBox button I want the check box in the header row of the DataGrid that I circled in blue to get checked.
If I click the Uncheck Header CheckBox button I want the check box in the header row of the DataGrid that I circled in blue to get unchecked.


In the Button click event of Button1 i have this:

DataGridEmployees_SelectAll.Checked = True

But I noticed the vb is not recognizing the CheckBox in the DataGrid's header and I get this message.


This is my code for my page.

Sample1.aspx

<%@ Page Language="VB" AutoEventWireup="false" CodeFile="Sample1.aspx.vb" Inherits="Sample1" %>

<!DOCTYPE html>

<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
    <title></title>
    <style type="text/css">
        .DGHeaderText {
            font-family: Arial;
            font-size: 12px;
            color: #000000;
            font-weight: bold;
        }

        .DGBodyText {
            font-family: Arial;
            font-size: 12px;
            color: #000000;
            font-weight: normal;
        }
    </style>
    <script type="text/javascript">
    </script>
</head>
<body>
    <form id="form1" runat="server">
        <div>
            <table>
                <tr>
                    <td>Check DataGrid Header CheckBox</td>
                    <td><asp:Button ID="Button1" runat="server" Text="Check Header CheckBox" /></td>                    
                </tr>
                <tr>
                    <td>Uncheck DataGrid Header CheckBox</td>
                    <td><asp:Button ID="Button2" runat="server" Text="Uncheck Header CheckBox" /></td>                    
                </tr>
            </table>
        </div>
        <div id="DivEmployees">
            <asp:DataGrid ID="DataGridEmployees" runat="server" AutoGenerateColumns="False" Font-Size="8pt" CellPadding="3" BorderColor="Black" Width="400px" CssClass="DGHeaderText">
                <Columns>
                    <asp:TemplateColumn HeaderText="EmployeeID">
                        <ItemTemplate>
                            <asp:Label ID="EmployeeID" CssClass="DGBodyText" Text='<%# DataBinder.Eval(Container.DataItem, "EmployeeID") %>' runat="server" />
                        </ItemTemplate>
                        <ItemStyle HorizontalAlign="Center" />
                    </asp:TemplateColumn>
                    <asp:TemplateColumn HeaderText="contract">
                        <HeaderTemplate>
                            <asp:CheckBox runat="server" ID="DataGridEmployees_SelectAll" autopostback="true" OnCheckedChanged="DataGridEmployees_SelectAll_Click" />
                            <%--<asp:CheckBox runat="server" ID="DataGridEmployees_SelectAll" autopostback="true" OnCheckedChanged="DataGridEmployees_SelectAll_Click"  ClientIDMode="Static" />--%>
                        </HeaderTemplate>
                        <ItemTemplate>
                            <asp:CheckBox ID="EmpId" runat="server" AutoPostBack="true" OnCheckedChanged="ChckedChanged" />
                        </ItemTemplate>
                    </asp:TemplateColumn>
                    <asp:TemplateColumn HeaderText="FirstName">
                        <ItemTemplate>
                            <asp:Label ID="FirstName" CssClass="DGBodyText" Text='<%# DataBinder.Eval(Container.DataItem, "FirstName") %>' runat="server" />
                        </ItemTemplate>
                    </asp:TemplateColumn>
                    <asp:TemplateColumn HeaderText="LastName">
                        <ItemTemplate>
                            <asp:Label ID="LastName" CssClass="DGBodyText" Text='<%# DataBinder.Eval(Container.DataItem, "LastName") %>' runat="server" />
                        </ItemTemplate>
                    </asp:TemplateColumn>
                    <asp:TemplateColumn HeaderText="Title">
                        <ItemTemplate>
                            <asp:Label ID="Title" CssClass="DGBodyText" Text='<%# DataBinder.Eval(Container.DataItem, "Title") %>' runat="server" />
                        </ItemTemplate>
                        <ItemStyle Wrap="False" />
                    </asp:TemplateColumn>
                    <asp:TemplateColumn HeaderText="PostalCode">
                        <ItemTemplate>
                            <asp:Label ID="PostalCode" CssClass="DGBodyText" Text='<%# DataBinder.Eval(Container.DataItem, "PostalCode") %>' runat="server" />
                        </ItemTemplate>
                    </asp:TemplateColumn>
                </Columns>
                <HeaderStyle HorizontalAlign="Center" />
            </asp:DataGrid>
            <br />
        </div> 
    </form>
</body>
</html>

Sample1.aspx.vb

Imports System.Data
Imports System.Data.SqlClient

Partial Class Sample1
    Inherits System.Web.UI.Page

    ' ----- Page Load Event -----
    Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load

        If Not IsPostBack Then
            BindDataGridEmployees()
        End If

    End Sub
    ' ----- Page Load Event -----

    ' ----- DataGrid Bind Function -----
    Private Sub BindDataGridEmployees()

        Dim constr As String = ConfigurationManager.ConnectionStrings("NorthwindConnectionString").ConnectionString

        Using mySqlConnection As SqlConnection = New SqlConnection(constr)

            mySqlConnection.Open()

            Dim mySqlCommand As SqlCommand = mySqlConnection.CreateCommand()
            ' sproc name
            mySqlCommand.CommandText = "NWEmployees_Get"
            mySqlCommand.CommandType = CommandType.StoredProcedure
            Dim mySqlDataAdapter As SqlDataAdapter = New SqlDataAdapter()
            mySqlDataAdapter.SelectCommand = mySqlCommand
            Dim ds As DataSet = New DataSet()
            mySqlDataAdapter.Fill(ds, "NWEmployees")
            DataGridEmployees.DataSource = ds.Tables("NWEmployees").DefaultView
            DataGridEmployees.DataBind()

            mySqlConnection.Close()

        End Using

    End Sub
    ' ----- DataGrid Bind Function -----

    ' ----- ASP CheckBox - Header Row Checkbox Changed Click Event -----
    Public Sub DataGridEmployees_SelectAll_Click(ByVal sender As Object, ByVal e As System.EventArgs)


    End Sub
    ' ----- ASP CheckBox - Header Row Checkbox Changed Click Event -----


    ' ----- Button Click - Check DataGrid Header CheckBox -----
    Protected Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click

        ' Check header checkbox

        'Call CheckHeaderCheckBox(sender, Me.DataGridEmployees)
        DataGridEmployees_SelectAll.Checked = True

    End Sub
    ' ----- Button Click - Check DataGrid Header CheckBox -----
    ' ----- Button Click - Uncheck DataGrid Header CheckBox -----
    Protected Sub Button2_Click(sender As Object, e As EventArgs) Handles Button2.Click

        ' Uncheck header checkbox
        'Call UncheckHeaderCheckBox(sender, Me.DataGridEmployees)
        DataGridEmployees_SelectAll.Checked = False

    End Sub

    ' ----- Button Click - Uncheck DataGrid Header CheckBox -----

    ' ----- asp check box click event - good -----
    Protected Sub ChckedChanged(ByVal sender As Object, ByVal e As EventArgs)



    End Sub
    ' ----- asp check box click event - good -----

    ' ----- Function - Check Header CheckBox of DataGrid -----
    Private Sub CheckHeaderCheckBox(ByVal sender As Object, ByRef DG As Web.UI.WebControls.DataGrid)

        Dim targetChkBox As CheckBox = DataGridEmployees.Controls(0).Controls(0).FindControl("DataGridEmployees_SelectAll")
        targetChkBox.Checked = False

    End Sub
    ' ----- Function - Check Header CheckBox of DataGrid -----

    ' ----- Function - Uncheck Header CheckBox of DataGrid -----
    Private Sub UncheckHeaderCheckBox(ByVal sender As Object, ByRef DG As Web.UI.WebControls.DataGrid)

        Dim targetChkBox As CheckBox = DataGridEmployees.Controls(0).Controls(0).FindControl("DataGridEmployees_SelectAll")
        targetChkBox.Checked = False

    End Sub
    ' ----- Function - Uncheck Header CheckBox of DataGrid -----



End Class

In my Sample1.aspx my CheckBox is in the HeaderTemplate in this line of code:

                        <HeaderTemplate>
                            <asp:CheckBox runat="server" ID="DataGridEmployees_SelectAll" autopostback="true" OnCheckedChanged="DataGridEmployees_SelectAll_Click" />
                        </HeaderTemplate>

I noticed that if I get this checkbox and take it out of the DataGrid and just put it on the page somewhere, then the button click event recognizes the checkbox.


How do i fix my example so the Button clicks check or uncheck the check box that is in my DataGrid's HeaderTemplate?