c# - 从 PreviousPage.FindControl 获取值

Question

我正在尝试为预订表格制作确认页面。而且我无法从我以前的页面控件中获取值。我的一切都在服务器上运行，我的提交按钮的 PostBackURL 指向确认页面。一切都会编译，但是当我输入信息并点击提交时，唯一弹出的是我的 bool 值，由于我的 if-elses，它并没有真正反射(reflect)真实的值(value)。我已经尝试了一百万种不同的类型转换/值(value)获取尝试，而当前的形式是我最接近的。任何帮助将不胜感激。 另外，我如何在 String.format 中获得像\n 这样的下一行？\n 似乎不起作用。 确认页面如下所示

ConfirmationPage.aspx.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;

public partial class Default2 : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {
            string numNights = Convert.ToString((TextBox)PreviousPage.FindControl("txtNights.Text"));
            string arrivalDate = Convert.ToString((TextBox)PreviousPage.FindControl("txtArrivalDate.Text"));
            string numAdults = Convert.ToString((DropDownList)PreviousPage.FindControl("ddlAdults.SelectedValue.Text"));
            string numChildren = Convert.ToString((DropDownList)PreviousPage.FindControl("ddlChildren.SelectedValue.Text"));
            string roomTypeBusiness = "false";
            string roomTypeSuite = "false";
            string roomTypeStandard = "false";
            string bedTypeKing = "false";
            string bedTypeDouble = "false";
            string smokingOption = "false";

            if (Convert.ToBoolean(PreviousPage.FindControl("rdoBusiness.Checked")))
                roomTypeBusiness = "true";
            else if (Convert.ToBoolean(PreviousPage.FindControl("rdoSuite.Checked")))
                roomTypeSuite = "true";
            else
                roomTypeStandard = "true";

            if (Convert.ToBoolean(PreviousPage.FindControl("rdoKing.Checked")))
                bedTypeKing = "true";
            else
                bedTypeDouble = "true";

            string specialRequests = Convert.ToString((TextBox)PreviousPage.FindControl("txtSpecialRequests.Text"));
            string name = Convert.ToString((TextBox)PreviousPage.FindControl("txtName.Text"));
            string email = Convert.ToString((TextBox)PreviousPage.FindControl("txtEmail.Text"));

            lblResults.Text = String.Format("Arrival Date: {0} \r\n Number of Nights: {1} \n Number of Adults: \r {2} Number of Children: {3} Business Room: {4} Suite Room: {5} Standard Room: {6} King Bed: {7} Double Bed: {8} Smoking: {9} Special Requests: {10} Name: {11} E-mail: {12}",
            arrivalDate, numNights, numAdults, numChildren, roomTypeBusiness, roomTypeSuite, roomTypeStandard, bedTypeKing, bedTypeDouble, smokingOption, specialRequests, name, email);
    }
}

上一页的aspx是

<%@ Page Title="" Language="C#" MasterPageFile="~/ResultsPageHTML5MasterPage/ResultsPageHTML5MasterPage.master" AutoEventWireup="true" CodeFile="ReservationForm_SqlInject.aspx.cs" Inherits="Default3" %>

<asp:Content ID="Content1" ContentPlaceHolderID="head" Runat="Server">
</asp:Content>
<asp:Content ID="Content2" ContentPlaceHolderID="ContentPlaceHolder1" Runat="Server">
    <h1>My Home Away From Home Hotels</h1>
        <h2>Where you&rsquo;re always treated like family</h2>
    <p>
        Arrival date: &nbsp;

        <asp:TextBox ID="txtArrivalDate" runat="server" Width="75px">TextBoxHere</asp:TextBox>
        &nbsp;

        <asp:ImageButton ID="ibtnCalendar" runat="server" ImageAlign="Top" ImageUrl="~/Images/Calendar.bmp" OnClick="ibtnCalendar_Click" />
    </p>
    <p>
        <asp:Calendar ID="clnArrival" runat="server" Visible="False" 
            OnSelectionChanged="clnArrival_SelectionChanged" BackColor="White" 
            BorderColor="Black" DayNameFormat="Shortest" Font-Names="Times New Roman" 
            Font-Size="10pt" ForeColor="Black" Height="220px" NextPrevFormat="FullMonth" 
            TitleFormat="Month" Width="400px">
            <DayHeaderStyle BackColor="#CCCCCC" Font-Bold="True" Font-Size="7pt" 
                ForeColor="#333333" Height="10pt" />
            <DayStyle Width="14%" />
            <NextPrevStyle Font-Size="8pt" ForeColor="White" />
            <OtherMonthDayStyle ForeColor="#999999" />
            <SelectedDayStyle BackColor="#CC3333" ForeColor="White" />
            <SelectorStyle BackColor="#CCCCCC" Font-Bold="True" Font-Names="Verdana" 
                Font-Size="8pt" ForeColor="#333333" Width="1%" />
            <TitleStyle BackColor="Black" Font-Bold="True" Font-Size="13pt" 
                ForeColor="White" Height="14pt" />
            <TodayDayStyle BackColor="#CCCC99" />
        </asp:Calendar>
    </p>
    <p>
        Number of nights: &nbsp;
        <asp:TextBox ID="txtNights" runat="server" Width="45px"></asp:TextBox>
    </p>
    <p>
        Number of Adults: &nbsp;
        <asp:DropDownList ID="ddlAdults" runat="server" Width="50px"></asp:DropDownList>
        &nbsp;&nbsp;
        Number of Children: &nbsp;
        <asp:DropDownList ID="ddlChildren" runat="server" Width="50px"></asp:DropDownList>
    </p>
    <h3>Preferences</h3>
    <p>
        Room Type: &nbsp;
        <asp:RadioButton ID="rdoBusiness" runat="server" GroupName="Room" Text="Business" />
        <asp:RadioButton ID="rdoStandard" runat="server" GroupName="Room" Text="Standard" />
        <asp:RadioButton ID="rdoSuite" runat="server" GroupName="Room" Text="Suite" />
    </p>
    <p>
        Bed Type:
        &nbsp;
        <asp:RadioButton ID="rdoKing" runat="server" GroupName="Bed" Text="King" />
        &nbsp;
        <asp:RadioButton ID="rdoDouble" runat="server" GroupName="Bed" Text="Double" />
    </p>
    <p>
        <asp:CheckBox ID="chkSmoking" runat="server" Text="Smoking" />
    </p>

    <p>
        Special Requests
    </p>
    <p>
        <asp:TextBox ID="txtSpecialRequests" runat="server" Rows="4" TextMode="MultiLine" Width="250px"></asp:TextBox>
    </p>
    <h3>Contact Information</h3>
    <p>Name:
    </p>

    <p>
        <asp:TextBox ID="txtName" runat="server" Width="320px"></asp:TextBox>
    </p>
    <p>
        Email
    </p>
    <p>
        <asp:TextBox ID="txtEmail" runat="server" Width="320px"></asp:TextBox>
    </p>

    <asp:Button ID="btnSubmit" runat="server" Text="Submit" 
         Width="80px" PostBackUrl="~/ConfirmationPage.aspx" />
    &nbsp;
    <asp:Button ID="btnClear" runat="server" Text="Clear" Width="80px" OnClick="btnClear_Click" />

    <p>
        <asp:Button ID="btnInstert" runat="server" Text="Insert" OnClick="btnInstert_Click" Width="80px" />
    </p>
    <p>
        <asp:Label ID="lblMessage" runat="server" Text="Label"></asp:Label>
    </p>
</asp:Content>

Answer 1

使用 PreviousPage.FindControl() 只能在有人从 Page A —> Transfer Data —> Page B 导航时访问 PreviousPage 数据。如果直接请求页面，则 PreviousPage 呈现空引用。

在这里，在您的情况下，一旦导航到页面 Default2，您只会在页面加载时保留值。在您点击提交后，您的 Default.aspx 会自行调用并且 PreviousPage 会丢失数据。此外，您找到控制权的方式不正确，您将获得 NULLREFERENCE。

More Info

如果您的 Web 应用程序中有母版页，则无法通过调用 PreviousPage.FindControl() 直接访问上一页控件，必须首先找到 ContentHolder 控件位于母版页中，然后可以在子网页中找到子控件。

Solution:-

使用IsPostBack属性

如何在 javascript 中获取 due_date 的值

public partial class Default2 : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {
        if (!IsPostBack)
        {
            string numNights = Convert.ToString(((TextBox)PreviousPage.Master.FindControl("ContentPlaceHolder1").FindControl("txtNights")).Text);
            string arrivalDate = Convert.ToString(((TextBox)PreviousPage.Master.FindControl("ContentPlaceHolder1").FindControl("txtArrivalDate")).Text);
            string numAdults = Convert.ToString(((DropDownList)PreviousPage.Master.FindControl("ContentPlaceHolder1").FindControl("ddlAdults")).SelectedValue);
            string numChildren = Convert.ToString(((DropDownList)PreviousPage.Master.FindControl("ContentPlaceHolder1").FindControl("ddlChildren")).SelectedValue);
            string roomTypeBusiness = "false";
            string roomTypeSuite = "false";
            string roomTypeStandard = "false";
            string bedTypeKing = "false";
            string bedTypeDouble = "false";
            string smokingOption = "false";

            if (Convert.ToBoolean(((RadioButton)PreviousPage.Master.FindControl("ContentPlaceHolder1").FindControl("rdoBusiness")).Checked"))
                roomTypeBusiness = "true";
            else if (Convert.ToBoolean(((RadioButton)PreviousPage.Master.FindControl("ContentPlaceHolder1").FindControl("rdoSuite")).Checked"))
                roomTypeSuite = "true";
            else
                roomTypeStandard = "true";

            if (Convert.ToBoolean(((RadioButton)PreviousPage.Master.FindControl("ContentPlaceHolder1").FindControl("rdoKing")).Checked))
                bedTypeKing = "true";
            else
                bedTypeDouble = "true";

            string specialRequests = Convert.ToString(((TextBox)PreviousPage.Master.FindControl("ContentPlaceHolder1").FindControl("txtSpecialRequests")).Text);
            string name = Convert.ToString(((TextBox)PreviousPage.Master.FindControl("ContentPlaceHolder1").FindControl("txtName")).Text);
            string email = Convert.ToString(((TextBox)PreviousPage.Master.FindControl("ContentPlaceHolder1").FindControl("txtEmail")).Text);

            /* Splitting data into newline */

            string info = String.Format("Arrival Date: {0}, Number of Nights: {1}, Number of Adults: {2}, Number of Children: {3}, Business Room: {4}, Suite Room: {5}, Standard Room: {6}, King Bed: {7}, Double Bed: {8}, Smoking: {9}, Special Requests: {10}, Name: {11}, E-mail: {12}",
            arrivalDate, numNights, numAdults, numChildren, roomTypeBusiness, roomTypeSuite, roomTypeStandard, bedTypeKing, bedTypeDouble, smokingOption, specialRequests, name, email);

            String[] tokens = info.Split(new[]{","}, StringSplitOptions.RemoveEmptyEntries);
            lblResults.Text = string.Join("<br />", tokens);        
            }
        }
    }