如何从控制事件中获取值到Page_Preinit在Asp.Net中的阶段？ [英] How Do I Get The Values From Control Events To Page_Preinit Phase In Asp.Net?
问题描述
我有一个aspx页面，我正在创建几个动态控件。
我也在Page_PreInit阶段重新创建所有这些动态控件，因为我需要渲染当事件发生或页面被发回服务器时它们。
但问题是，我想从控件DropDownList中检索所选值DropDownlist Change事件发生时。由于我在PreInit阶段重新创建所有动态控件，我无法在该阶段获得Dropdownlist选择值。？
请指教。
提前致谢。
代码例。
I have a aspx page where i am creating several dynamic controls.
I am also Re-creating all these dynamic controls in Page_PreInit phase since i need to render them when an event happens or when the page is posted back to server.
But Now the problem is, i want to retrieve the selected value from a control "DropDownList" when the DropDownlist Change event occurs. And Since i am Re-creating all Dynamic Controls in PreInit phase, i cannot get the Dropdownlist selected value in that phase.?
Please advise.
Thanks in advance.
Code Ex.
protected void Page_PreInit(object sender, EventArgs e)
{
//recreating all dyn controls on every postback in order to access them..
if (IsPostBack)
{
Custom_Org_Chart.Draw_Entire_Chart(this.Page, form1,this.GetType(),Convert.ToInt32(DropDownList1.SelectedItem.Value));
}
}
此处将根据DropDownlist选择的项目值呈现动态控件
但是（DropDownList1.SelectedItem.Value）将抛出NullRefrenceException。
注意：
1.我试图得到OverRiding Pre-Render事件的值，但它不起作用..
2.还尝试重新创建DropDownList Change事件的所有动态控件，它抛出了重复ID的发现错误，因为控件正在创建两次..
Here the Dynamic controls will be rendered, based on the DropDownlist Selected Item Value
but (DropDownList1.SelectedItem.Value) will throw NullRefrenceException.
Note:
1. I tried to get the value by OverRiding Pre-Render Event, but it didn't work..
2. Also tried re-creating all dynamic controls on DropDownList Change event, it threw duplicate ID's found error, since controls were creating twice..
推荐答案
您需要使用Page OnInit事件来创建动态控件。
< a href =http://msdn.microsoft.com/en-us/library/cd6at422(v=vs.110).aspx> http://msdn.microsoft.com/en-us/library/cd6at422（ v = vs.110）.aspx [ ^ ]
You need to use the Page OnInit event to create dynamic controls.
http://msdn.microsoft.com/en-us/library/cd6at422(v=vs.110).aspx[^]
我认为你真正得到的是if（isPostBack）。看起来很奇怪，你想要在回发时重新创建动态控件，但由于网页是无状态的，它不知道你的控件是什么了。我自己做了一点运动来证明这一点。在aList_SelectedIndexChanged事件上放置一个断点，它将在回发时使用正确的值访问它。
I think what's really getting you is the if(isPostBack). It seems weird, that you'd want to recreate your dynamic controls on postback, but since a web page is stateless, it doesn't know what your control is anymore. I did a little exercise myself to prove it. Put a breakpoint on the aList_SelectedIndexChanged event and it will visit it on postback with the right value.
<%@ Page Language="C#" AutoEventWireup="true" CodeFile="Default.aspx.cs" Inherits="_Default" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
<title></title>
</head>
<body>
<form id="form1" runat="server">
<asp:Panel ID="pnlMain" runat="server" Style="width: 100%;">
</asp:Panel>
</form>
</body>
</html>
using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
public partial class _Default : System.Web.UI.Page
{
protected override void OnPreInit(EventArgs e)
{
base.OnPreInit(e);
CreateDropDown();
}
protected void Page_Load(object sender, EventArgs e)
{
}
private void CreateDropDown()
{
DropDownList aList = new DropDownList();
for (int i = 0; i < 5; i++)
{
aList.Items.Add(new ListItem(i.ToString(), i.ToString()));
}
aList.SelectedIndexChanged += new EventHandler(aList_SelectedIndexChanged);
aList.AutoPostBack = true;
pnlMain.Controls.Add(aList);
}
private void aList_SelectedIndexChanged(object sender, EventArgs e)
{
DropDownList aList = (DropDownList)sender;
int i = -1;
if (Int32.TryParse(aList.SelectedValue, out i))
{
//good to go
}
}
}
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