有以下兩個頁面Default.aspx和Result.aspx,代碼如下:
<!-- Default.aspx -->
<%@ Page Language="C#" AutoEventWireup="true" MasterPageFile="~/Default.master" CodeFile="Default.aspx.cs" Inherits="_Default" %>
<asp:Content ID="Content1" runat="server" ContentPlaceHolderID="ContentPlaceHolder1">
<asp:Label ID="Label1" runat="server" Text="Please input a string here"></asp:Label>
<asp:TextBox ID="TextBox1" runat="server"></asp:TextBox>
<asp:Button ID="Button1" runat="server" Text="Button" PostBackUrl="~/Result.aspx" /></asp:Content>
<!-- Default.aspx -->
<%@ Page Language="C#" AutoEventWireup="true" MasterPageFile="~/Default.master" CodeFile="Default.aspx.cs" Inherits="_Default" %>
<asp:Content ID="Content1" runat="server" ContentPlaceHolderID="ContentPlaceHolder1">
<asp:Label ID="Label1" runat="server" Text="Please input a string here"></asp:Label>
<asp:TextBox ID="TextBox1" runat="server"></asp:TextBox>
<asp:Button ID="Button1" runat="server" Text="Button" PostBackUrl="~/Result.aspx" /></asp:Content>
//Default.aspx.cs
using System;
using System.Data;
using System.Configuration;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.WebControls;
//using System.Web.UI.WebControls.WebParts;
using System.Web.UI.HtmlControls;
using System;
using System.Data;
using System.Configuration;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.WebControls;
//using System.Web.UI.WebControls.WebParts;
using System.Web.UI.HtmlControls;
public partial class _Default : System.Web.UI.Page
{
protected void Page_Load(object sender, EventArgs e)
{
}
}
{
protected void Page_Load(object sender, EventArgs e)
{
}
}
<!-- Result.aspx -->
<%@ Page Language="C#" MasterPageFile="~/Default.master" AutoEventWireup="true" CodeFile="Result.aspx.cs" Inherits="Result" Title="Untitled Page" %>
<asp:Content ID="Content1" ContentPlaceHolderID="ContentPlaceHolder1" Runat="Server">
<asp:Label ID="Label1" runat="server" Text="The string you input in the previous page is"></asp:Label>
<asp:TextBox ID="TextBox1" runat="server"></asp:TextBox>
</asp:Content>
//Result.aspx.cs
using System;
using System.Data;
using System.Configuration;
using System.Collections;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Web.UI.HtmlControls;
<%@ Page Language="C#" MasterPageFile="~/Default.master" AutoEventWireup="true" CodeFile="Result.aspx.cs" Inherits="Result" Title="Untitled Page" %>
<asp:Content ID="Content1" ContentPlaceHolderID="ContentPlaceHolder1" Runat="Server">
<asp:Label ID="Label1" runat="server" Text="The string you input in the previous page is"></asp:Label>
<asp:TextBox ID="TextBox1" runat="server"></asp:TextBox>
</asp:Content>
//Result.aspx.cs
using System;
using System.Data;
using System.Configuration;
using System.Collections;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Web.UI.HtmlControls;
public partial class Result : System.Web.UI.Page
{
protected void Page_Load(object sender, EventArgs e)
{
if (PreviousPage != null)
{
TextBox tb = (TextBox)PreviousPage.FindControl("TextBox1");
if (tb != null)
TextBox1.Text = tb.Text;
}
}
}
{
protected void Page_Load(object sender, EventArgs e)
{
if (PreviousPage != null)
{
TextBox tb = (TextBox)PreviousPage.FindControl("TextBox1");
if (tb != null)
TextBox1.Text = tb.Text;
}
}
}
這兩個頁面都指定了MasterPageFile屬性。因爲該MasterPage中的內容無關緊要,就不列出來了。在Default.aspx上有兩個控件:TextBox1用於接受用戶的輸入,Button1用於提交頁面,其PostBackUrl指向Result.aspx。在Result.aspx.cs的Page_Load方法中嘗試在TextBox1中顯示用戶在前一頁面的TextBox1中輸入的字符串。當執行以下語句時:
TextBox tb = (TextBox)PreviousPage.FindControl("TextBox1");
tb的值爲null。將以上語句更改爲如下代碼:
Content con = (Content)PreviousPage.FindControl("Content1");
if (con == null)
return;
if (con == null)
return;
TextBox tb = (TextBox)con.FindControl("TextBox1");
但con的值爲null,這樣後續的語句也不可能執行了。問題出在哪裏呢?
經過一番搜索,在forums.asp.net中找到了答案,以下引用的是bitmask的說法:
...becasue the Content controls themselves dissapear after the master page rearranges the page. You can use the ContentPlaceHolders, or the <form> on the MasterPage if there are no INamingContainers between the form and the control you need.
...becasue the Content controls themselves dissapear after the master page rearranges the page. You can use the ContentPlaceHolders, or the <form> on the MasterPage if there are no INamingContainers between the form and the control you need.
所以以上的代碼應該改成:
TextBox tb = (TextBox)PreviousPage.Master.FindControl("ContentPlaceHolder1").FindControl("TextBox1");
bitmask還在他的博客上寫了一篇文章來闡述FindControl方法和INamingContainers接口:
http://www.odetocode.com/Articles/116.aspx
http://www.odetocode.com/Articles/116.aspx