ASP.NET Check All CheckBoxes in Grid WebForm

gistfile1.cs

//Check All CheckBoxes in Grid WebForm

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        protected void CheckBoxAll_CheckedChanged(object sender, EventArgs e)
        {
            var chkAll = (CheckBox)GridMemberList.HeaderRow.FindControl("CheckBoxAll");
            if (chkAll.Checked)
            {
                foreach (var chkSelected in from GridViewRow gvRow in GridMemberList.Rows 
                                            select (CheckBox)gvRow.FindControl("ChecAttItem"))
                {
                    chkSelected.Checked = true;
                }
            }
            else
            {
                foreach (
                    var chkSel in
                        from GridViewRow gvRow in GridMemberList.Rows
                        select (CheckBox)gvRow.FindControl("ChecAttItem"))
                {
                    chkSel.Checked = false;
                }
            }
        }


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                                            <Columns>
                                                <asp:TemplateField HeaderText="Attended" SortExpression="Attended">
                                                    <HeaderTemplate>
                                                            <asp:CheckBox runat="server" ID="CheckBoxAll" ClientIDMode="Static" AutoPostBack="true"
                                                                OnCheckedChanged="CheckBoxAll_CheckedChanged" Text="Select *" />
                                                        <asp:HiddenField runat="server" ID="EmployeeId" Value='<%# Bind("Employee") %>' />
                                                    </HeaderTemplate>
                                                    <ItemTemplate>
                                                        <asp:CheckBox ID="ChecAttItem" runat="server" Checked='<%# Bind("Attended") %>' /><asp:HiddenField
                                                            runat="server" ID="EmployeeId" Value='<%# Bind("CommitteeCreationMember1") %>' />
                                                    </ItemTemplate>
                                                </asp:TemplateField>
                                                <asp:TemplateField HeaderText="Committee Member" SortExpression="Employee1">
                                              ..........................
                                                </asp:TemplateField>
                                             ..................
                                            </Columns>
                                        </asp:GridView>
                                    

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