全选gridView中的复选框

<asp:CheckBox ID="CheckAll" runat="server" Text="全选" OnCheckedChanged="selectAll" AutoPostBack="True" />

 protected void selectAll(object sender, EventArgs e)
    {
        //如果选中，则全选；否则，取消选择
        if (CheckAll.Checked == false)
        {
            for (int i = 0; i < GridView1.Rows.Count; i++)
            {
                CheckBox chk = (CheckBox)(GridView1.Rows[i].Cells[0].FindControl("ChBSelect"));
                chk.Checked = false;
            }
        }
        else
        {
            for (int i = 0; i < GridView1.Rows.Count; i++)
            {
                CheckBox chk = (CheckBox)(GridView1.Rows[i].Cells[0].FindControl("ChBSelect"));
                chk.Checked = true;
            }
        }
    }