Asp.net – Accessing Check box control that is in column header

To get/use and enjoy the value of the check box in the heading?

You can use find control against the GridView.HeaderRow.

So, assuming this markup:

<asp:Button ID="cmdLoad" runat="server" Text="Load Data"
    CssClass="btn"
    OnClick="cmdLoad_Click"
    />
<br />
<br />

<asp:GridView ID="GVHotels" runat="server" AutoGenerateColumns="False"
    DataKeyNames="ID" CssClass="table" 
    Width="45%"
    ShowHeaderWhenEmpty="true"
    >
    <Columns>
        <asp:BoundField DataField="FirstName" HeaderText="FirstName" />
        <asp:BoundField DataField="LastName" HeaderText="LastName" />
        <asp:BoundField DataField="City" HeaderText="City" />
        <asp:BoundField DataField="HotelName" HeaderText="HotelName" />
        <asp:BoundField DataField="Description" HeaderText="Description" />
        <asp:TemplateField 
            ItemStyle-HorizontalAlign="Center"
            HeaderStyle-HorizontalAlign="Center"
            >
            <ItemTemplate>
                <asp:CheckBox ID="chkSel" runat="server" 
                    OnCheckedChanged="chkSel_CheckedChanged"
                    AutoPostBack="true"
                    />
            </ItemTemplate>
            <HeaderTemplate>
                <div style="text-align:center">
                    Select All<br />
                <asp:CheckBox ID="chkSelAll" runat="server"
                    OnCheckedChanged="chkSelAll_CheckedChanged"
                    AutoPostBack="true"
                    />
                </div>
            </HeaderTemplate>
        </asp:TemplateField>
    </Columns>
</asp:GridView>

So, when we hit the button to load the GridView, we then will get the value of the check box in the heading, and set all rows to checked (or un-checked).

So, the code to load our grid looks like this:

    protected void Page_Load(object sender, EventArgs e)
    {
    }
    protected void cmdLoad_Click(object sender, EventArgs e)
    {
        LoadGrid();
    }

    void LoadGrid()
    {

        CheckBox chkSelAll = new CheckBox();
        chkSelAll.Checked = false;
        bool HoldCheck = false;
        if (GVHotels.Rows.Count > 0)
        {
            chkSelAll = (CheckBox)GVHotels.HeaderRow.FindControl("chkSelAll");
            HoldCheck = chkSelAll.Checked; 
        }

        string strSQL = @"SELECT * FROM tblHotelsA
                          ORDER BY HotelName";

        GVHotels.DataSource = General.MyRst(strSQL);
        GVHotels.DataBind();

        chkSelAll = (CheckBox)GVHotels.HeaderRow.FindControl("chkSelAll");
        chkSelAll.Checked = HoldCheck;  

        CheckAll(chkSelAll.Checked);
    }

    protected void chkSel_CheckedChanged(object sender, EventArgs e)
    {

    }

    protected void chkSelAll_CheckedChanged(object sender, EventArgs e)
    {
        CheckBox chkSelAll = (CheckBox)sender;
        CheckAll(chkSelAll.Checked);
    }

    void CheckAll(bool chk)
    {
        // check/un check all check box for each row

        foreach (GridViewRow gRow in GVHotels.Rows)
        {
            CheckBox chkSel = (CheckBox)gRow.FindControl("chkSel");
            chkSel.Checked = chk;
        }
    }

Note VERY close, that WHEN we re-bind the GridView, then the setting of the check box is lost. So, if we are to re-bind the GridView, but ALSO respect the check box, then we get/grab/save the check box, re-load grid, and then re-set the check box back into the heading. (the value is LOST when we re-bind, so above code takes this into account).

Note that after the grid loads, one might still want to check all (or un-check all) by clicking on the header. That code is somewhat easier since we can use "sender" to get the check box in question.

So, that code is:

    protected void chkSelAll_CheckedChanged(object sender, EventArgs e)
    {
        CheckBox chkSelAll = (CheckBox)sender;
        CheckAll(chkSelAll.Checked);
    }

And the result is thus this: