当另一个文本框触发OnTextChanged事件时，访问Gridview中的文本框值

我正在向gridview添加过滤器。其中一列是日期字段，我有两个文本框，以便用户可以输入范围。在用户输入第二个日期之后，将触发Event。

但是，我无法访问第一个文本框中的数据。我得到一个错误，对象尚未设置。

这是标记:

asp:TemplateField HeaderText="Open Date" SortExpression="RegistrationOpen">
            <HeaderTemplate>
                <asp:LinkButton runat="server" ID="lbOpenDate" Text="Open Date" CommandName="Sort" CommandArgument="OpenDate"></asp:LinkButton>
                <asp:TextBox runat="server" ID="txtBoxOpenDateFilterStart" CssClass="datepick"></asp:TextBox>
                <asp:Label runat="server" ID="lblOpenDateFilter" Text="To"></asp:Label>
                <asp:TextBox runat="server" ID="txtBoxOpenDateFilterEnd" AutoPostBack="true" OnTextChanged="txtBoxFilter_TextChanged" CssClass="datepick"></asp:TextBox>
            </HeaderTemplate>

这是OnTextChanged事件:

protected void txtBoxFilter_TextChanged(object sender, EventArgs e)
    {
        try
        {
            if (sender is TextBox)
            {
                populateSectionGrid();
                DataTable dtSectionGridData = SectionGridView.DataSource as DataTable;
                Nullable<DateTime> tdtStartDate;
                Nullable<DateTime> tdtEndDate;
                if (dtSectionGridData != null)
                {
                    TextBox txtBox = (TextBox)sender;

                    if (txtBox.ID.Equals("txtBoxOpenDateFilterEnd"))
                    {
                        SectionGridViewFilterExpression = string.Empty;
                        //Get the start date
                        string tstrStartDate = (SectionGridView.FindControl("txtBoxOpenDateFilterStart") as TextBox).Text; ''This is the problem. This Control is returned as not set even though there is a date in the text box.
                        if (!String.IsNullOrWhiteSpace(tstrStartDate))
                        {
                            tdtStartDate = setStartTime(tstrStartDate);
                            tstrStartDate = "RegistrationOpen >= #" + tdtStartDate + "#";
                        }
                        //Get the end date     
                        string tstrEndDate = string.Empty;
                        if (!String.IsNullOrWhiteSpace(txtBox.Text))
                        {
                            tdtEndDate = setStartTime(txtBox.Text);
                            tstrEndDate = "RegistrationOpen <= #" + tdtEndDate + "#";
                        }
                        if (String.IsNullOrWhiteSpace(tstrEndDate))
                        {
                            SectionGridViewFilterExpression = tstrStartDate;
                        }
                        else
                        {
                            SectionGridViewFilterExpression = tstrStartDate +  " AND " + tstrEndDate;
                        }                       
                    }
                    DataRow[] drFound = dtSectionGridData.Select(SectionGridViewFilterExpression);
                    dtSectionGridData = drFound.CopyToDataTable();
                    SectionGridView.DataSource = dtSectionGridData;
                    SectionGridView.DataBind();
                }
            }
        }
        catch (Exception ex)
        {
            logger.ErrorException(ex.Message, ex);
            Response.Redirect("~/Error.aspx");
        }
    }

我怎么能访问第一个文本框("txtBoxOpenDateFilterStart")当事件触发的文本框("txtBoxOpenDateFilterEnd")?

我发现一些代码具有相同的功能，我需要使用2个文本框。我更改了标记，使只有第二个文本框触发事件，而用于从第一个文本框获取数据的函数使用:

(GridView.HeaderRow.FindControl("controlID") as TextBox).Text

但是，当我使用这个函数时，文本框是空的。我输入了一个日期，但是当我读取它时，文本框是空的。我做错了什么?这是我对标题列的标记:

 <HeaderTemplate>
                <asp:LinkButton runat="server" ID="lbOpenDate" Text="Reg. Open Date" CommandName="Sort" CommandArgument="OpenDate"></asp:LinkButton>
                <table>
                    <tr>
                        <td><asp:TextBox runat="server" ID="txtBoxOpenDateFilterStart" AutoPostBack="true" CssClass="datepick"></asp:TextBox></td>
                        <td><asp:Label runat="server" ID="lblOpenDateFilter" Text="To"></asp:Label></td>
                        <td><asp:TextBox runat="server" ID="txtBoxOpenDateFilterEnd" AutoPostBack="true" OnTextChanged="txtBoxFilter_TextChanged" CssClass="datepick"></asp:TextBox></td>
                    </tr>
                </table>
            </HeaderTemplate>

这是与该列相关的方法调用:

 protected void txtBoxFilter_TextChanged(object sender, EventArgs e)
    {
        try
        {
            if (sender is TextBox)
            {
                populateSectionGrid();
                DataTable dtSectionGridData = SectionGridView.DataSource as DataTable;
                Nullable<DateTime> tdtStartDate;
                Nullable<DateTime> tdtEndDate;
                if (dtSectionGridData != null)
                {
                    TextBox txtBox = (TextBox)sender;
else if (txtBox.ID.Equals("txtBoxOpenDateFilterEnd"))
                    {
                        SectionGridViewFilterExpression = string.Empty;
                        //Get the start date
                        string temp = (SectionGridView.HeaderRow.Cells[4].FindControl("txtBoxOpenDateFilterStart") as TextBox).Text;
                        string tstrStartDate = (SectionGridView.HeaderRow.FindControl("txtBoxOpenDateFilterStart") as TextBox).Text;
                        if (!String.IsNullOrWhiteSpace(tstrStartDate))
                        {
                            tdtStartDate = setStartTime(tstrStartDate);
                            tstrStartDate = "RegistrationOpen >= #" + tdtStartDate + "#";
                        }
                        //Get the end date     
                        string tstrEndDate = string.Empty;
                        if (!String.IsNullOrWhiteSpace(txtBox.Text))
                        {
                            tdtEndDate = setStartTime(txtBox.Text);
                            tstrEndDate = "RegistrationOpen <= #" + tdtEndDate + "#";
                        }
                        if (String.IsNullOrWhiteSpace(tstrEndDate))
                        {
                            SectionGridViewFilterExpression = tstrStartDate;
                        }
                        else if (String.IsNullOrWhiteSpace(tstrStartDate))
                        {
                            SectionGridViewFilterExpression = tstrEndDate;
                        }
                        else
                        {
                            SectionGridViewFilterExpression = tstrStartDate + " AND " + tstrEndDate;
                        }                       
                    }
                    DataRow[] drFound = dtSectionGridData.Select(SectionGridViewFilterExpression);
                    dtSectionGridData = drFound.CopyToDataTable();
                    SectionGridView.DataSource = dtSectionGridData;
                    SectionGridView.DataBind();
                }
            }

sp:TemplateField HeaderText="Open Date" SortExpression="RegistrationOpen">

sp:TemplateField HeaderText="Open Date">