How Do I Get The Values From Control Events To Page_Preinit Phase In Asp.Net?

Question

4.00/5 (1 vote)

See more:

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.

C#

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));
        }
    }

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..

Posted 10-Jun-14 21:10pm

Prathap S V

Updated 10-Jun-14 21:15pm

v3

Add a Solution

2 solutions

Solution 1

You need to use the Page OnInit event to create dynamic controls.

http://msdn.microsoft.com/en-us/library/cd6at422(v=vs.110).aspx[^]

Posted 11-Jun-14 15:16pm

ZurdoDev

Add a Solution

Add your solution here

Treat my content as plain text, not as HTML

Preview 0

…

Existing Members

Sign in to your account

...or Join us

Download, Vote, Comment, Publish.

Your Email
Password
Forgot your password?

Your Email
This email is in use. Do you need your password?
Optional Password

I have read and agree to the Terms of Service and Privacy Policy
Please subscribe me to the CodeProject newsletters

When answering a question please:

Read the question carefully.
Understand that English isn't everyone's first language so be lenient of bad spelling and grammar.
If a question is poorly phrased then either ask for clarification, ignore it, or edit the question and fix the problem. Insults are not welcome.
Don't tell someone to read the manual. Chances are they have and don't get it. Provide an answer or move on to the next question.

Let's work to help developers, not make them feel stupid.

This content, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

jasonHall · Accepted Answer · 2014-06-12T10:42:00

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.

ASP.NET

<%@ 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>

C#

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
        }
    }
}