在代码前面设置的用户控件属性在OnPreRender中为null [英] User control property set in code front is null in OnPreRender
问题描述
TestPage 有一个属性 Items ，我想传递到我的自定义用户控件 Control 中.我喜欢在代码前设置属性的语法，因此TestPage.aspx看起来像这样……
TestPage has a property Items I want to pass into my custom user control Control. I like the syntax of setting the property in code-front, so TestPage.aspx looks like this...
页面:
<%@ Page Language="C#" AutoEventWireup="true" CodeFile="TestPage.aspx.cs" Inherits="TestPage" %>
<%@ Register Src="~/Control.ascx" TagPrefix="custom" TagName="Control" %>
<!DOCTYPE html>
<html xmlns="http://www.w3.org/1999/xhtml">
<head><title>Test Page</title></head>
<body>
<custom:Control ID="TestControl" Items='<%# Items %>' runat="server" />
</body>
</html>
TestPage 的
后置代码具有 Items 属性和一个简单的getter:
Code-behind for TestPage has the property Items with a simple getter:
using System;
using System.Collections.Generic;
using System.Web.UI;
public partial class TestPage : Page
{
protected List<string> Items = new List<string>() { "Hello", "world!", };
}
控件:
我的自定义用户控件具有一个中继器，以呈现 Items 中的值.
My custom user control has a repeater to render the values in Items.
<%@ Control Language="C#" AutoEventWireup="true" CodeFile="Control.ascx.cs" Inherits="Control" %>
<asp:Repeater ID="Repeater" ItemType="System.string" runat="server">
<ItemTemplate>
<p><%# Item %></p>
</ItemTemplate>
</asp:Repeater>
该控件的隐藏代码公开了公共 Items 属性，并将其绑定到 Repeater .
The control's code-behind exposes the public Items property and binds it to the Repeater.
using System;
using System.Collections.Generic;
using System.Web.UI;
public partial class Control : UserControl
{
public List<string> Items { get; set; }
protected override void OnPreRender(EventArgs e)
{
Repeater.DataSource = Items;
Repeater.DataBind();
}
}
问题:
呈现的页面为空，因为 OnPreRender 中的 Control.Items == null .
The rendered page is empty, because Control.Items == null in OnPreRender.
如果我在 TestPage.Page_Load 中设置 TestControl.Items = Items ，则会在 Control.OnPreRender <中填充 Control.Items /code>.
If I set TestControl.Items = Items in TestPage.Page_Load, Control.Items is populated in Control.OnPreRender.
那行得通，但是我很书呆子.在 TestPage 的代码前端中设置 Items 时，是否可以绑定转发器?
That works, but I'm pedantic. Is it possible to bind the repeater when Items is set in TestPage's code front?
推荐答案
<custom:Control ID="TestControl" Items='<%# Items %>' runat="server" />
仅在您调用控件的DataBind方法时执行:
will only be performed if you call the DataBind method of the control:
TestControl.DataBind();
如果页面具有其他数据绑定表达式，则可以选择调用 Page.DataBind()，它将递归绑定所有子控件.
If your page has other data-binding expressions, you can alternatively call Page.DataBind(), which will recursively bind all child controls.
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