Question

ASP.NET C# - Dynamically adding table rows & cells issue.

Asked by: orrsafety

I'm trying to click a linkbutton and have more rows added to a table via server side code. I will adding controls that I can iterate through later. Every time the link button it clicked, I want another NEW row to be added. However, when clicked... one new row is added, but that's it. When clicked again, it seems that the row is that is just added is lost and the same row is re-added. ViewState not being enabled doesn't seem to be the problem, as I have it enabled ever where I can think of. Maybe my understanding of how postback and viewstate works is incorrect. I would expect that when you have a session on the server and viewstate enabled that when a control is dynamically added via postback, it would persist until you leave the page. Anyone have any ideas? I'm sure someone has come across this before.

<%@ Page Language="C#" EnableViewState="true" EnableSessionState="True" AutoEventWireup="true" CodeFile="ajaxtest.aspx.cs" Inherits="ajaxtest" %>
 
<!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>Untitled Page</title>
</head>
<body>
    
    <form id="form1" runat="server" enableviewstate="true">
  
        <asp:LinkButton ID="LinkButton1" runat="server" onclick="LinkButton1_Click">LinkButton</asp:LinkButton>
        <asp:Table runat="server" ID="MyTable" EnableViewState="true">
            <asp:TableRow>
                <asp:TableCell>
                Exsisting Row
                </asp:TableCell>
            </asp:TableRow>
        </asp:Table>
        
        
    
    </form>
</body>
</html>
 
 
using System;
using System.Collections;
using System.Configuration;
using System.Data;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.HtmlControls;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
 
public partial class ajaxtest : System.Web.UI.Page
{    
    int Counter = 0;
 
    protected void Page_Load(object sender, EventArgs e)
    {
        
 
    }
 
    protected void LinkButton1_Click(object sender, EventArgs e)
    {
        TableCell NewCell = new TableCell();
        TableRow NewRow = new TableRow();
 
        Counter++; 
        NewCell.Text = "Dynamically Added " + Counter.ToString();
        
        NewRow.Cells.Add(NewCell);
        MyTable.Rows.Add(NewRow);
    }
}

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Asked On: 2009-07-01 at 07:47:06ID24536592
Tags: asp.net
,; dynamic controls
,; table
,; row
,; cell
Topics: Programming for ASP.NET
,; Microsoft Visual C#.Net
,; C# Programming Language
Participating Experts: 2
Points: 500
Comments: 7

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Answers

by: ged325Posted on 2009-07-01 at 07:53:49ID: 24754965

After the rows.Add

MyTable.DataBind();

DataBind syncs up the changes.

by: orrsafetyPosted on 2009-07-01 at 07:58:44ID: 24755029

I gave that a shot, but that didn't do it. I'm still only getting one new row. Also to clarify, this is not a "gridview" and I'm not working with any data that's getting bound. Thanks for time and suggestion.

by: orrsafetyPosted on 2009-07-01 at 08:06:59ID: 24755124

I'm working with the .net 2.0 framework, I tried with 3.5 as well and I'm still getting the same issue. Don't know if that helps?

by: crazymanPosted on 2009-07-01 at 08:28:42ID: 24755365

Dynamically created controls must be re-created on each postback see : http://www.singingeels.com/Articles/Dynamically_Created_Controls_in_ASPNET.aspx

Since you add the table row and then next postback you dont re-add the one you already added, it wont get re-created.

You could create list held in view state, something like :

public List<string> Items
{
get {return this.ViewState["Items"] ?? new List<string>();
set {this.ViewState["Items"] = value;
}

then in your button click do something like

List<string> lst = this.Items;
lst.Add("New Item");
this.Items = lst;

then override CreateChildControls and do something like

foreach (string str in this.Items)
{
TableCell NewCell = new TableCell();
TableRow NewRow = new TableRow();
NewCell.Text = String.Format("Added Cell {0}",str);
NewRow.Cells.Add(NewCell);
MyTable.Rows.Add(NewRow);

}

by: crazymanPosted on 2009-07-01 at 08:43:30ID: 24755527

This works ok for me


<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
    <title></title>
</head>
<body>
    <form id="form1" runat="server">
    <asp:LinkButton ID="LinkButton1" runat="server" onclick="LinkButton1_Click">LinkButton</asp:LinkButton>
        <asp:Table runat="server" ID="MyTable" EnableViewState="true">
            <asp:TableRow>
                <asp:TableCell>
                Exsisting Row
                </asp:TableCell>
            </asp:TableRow>
        </asp:Table>
 
    </form>
</body>
</html>
=============================================================CODEBEHIND
 
using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
 
public partial class Test : System.Web.UI.Page
{
    public List<string> Items
    {
        get { return (List<string>)this.ViewState["Items"] ?? new List<string>(); }
        set {this.ViewState["Items"] = value;}
    }
 
    protected void LinkButton1_Click(object sender, EventArgs e)
    {
        string txt = DateTime.Now.ToString();
        List<string> lst = this.Items;
        lst.Add(txt);
        this.Items = lst;
        RenderTableItem(txt);
 
    }
 
    protected override void CreateChildControls()
    {
        //Save any existing that were added via markup
        RenderTable();
    }
 
    private void RenderTable()
    {
        foreach (string str in this.Items)
        {
            RenderTableItem(str);
        }
    }
    private void RenderTableItem(string str)
    {
        TableCell NewCell = new TableCell();
        TableRow NewRow = new TableRow();
        NewCell.Text = String.Format("Added Cell {0}", str);
        NewRow.Cells.Add(NewCell);
        MyTable.Rows.Add(NewRow);
    }
 
}

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by: orrsafetyPosted on 2009-07-01 at 09:03:18ID: 24755717

Well I think this certainly puts me on the right track. I wasn't aware of that process. Thank you very much!

by: orrsafetyPosted on 2009-07-01 at 09:27:03ID: 24755929

Since I was only concerned with a single table. This is what I ended up doing. I saved the table to a session variable session variable which is nice cause it saves everything in the table. I set a temp table to the session saved table or if that doesn't exists to the table on the page. I make all the modifications to that, then place it back in the page and save to the session variable. This works exactly like I wanted it to.

<%@ 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>Untitled Page</title>
</head>
<body>
    <form id="form1" runat="server">
    <div>
        <asp:LinkButton ID="LinkButton1" runat="server" onclick="LinkButton1_Click">LinkButton</asp:LinkButton>
        
        <asp:Panel ID="TableContainer" runat="server">
            <asp:Table ID="TableOnThePage" runat="server">
                <asp:TableRow>
                    <asp:TableCell>Exsisting Row</asp:TableCell>
                </asp:TableRow>
            </asp:Table>
        </asp:Panel>
    </div>
    </form>
</body>
</html>
 
=====================================================================
 
using System;
using System.Configuration;
using System.Data;
using System.Linq;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.HtmlControls;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Xml.Linq;
 
public partial class _Default : System.Web.UI.Page 
{
    
    protected void Page_Load(object sender, EventArgs e)
    {
        if (IsPostBack)
        {
            if (Session["PersistentTable"] != null)
            {
                TableContainer.Controls.Remove(TableOnThePage);
                TableContainer.Controls.Add((Table)Session["PersistentTable"]);
            }
        }
        else
        {
            if (Session["PersistentTable"] != null) Session["PersistentTable"] = null;
        }
    }
 
    protected void LinkButton1_Click(object sender, EventArgs e)
    {
        Table TempTable = new Table();
        if (Session["PersistentTable"] != null) TempTable = (Table)Session["PersistentTable"];
        else TempTable = TableOnThePage; 
        
 
        TableCell NewCell = new TableCell();
        TableRow NewRow = new TableRow();
 
        NewCell.Text = "Dynamically Added " + TempTable.Rows.Count.ToString();
 
        NewRow.Cells.Add(NewCell);
        TempTable.Rows.Add(NewRow);
 
        TableContainer.Controls.Remove(TableOnThePage);
        TableContainer.Controls.Add(TempTable);
        Session["PersistentTable"] = TempTable;
        
    }
}

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ASP.NET C# - Dynamically adding table rows & cells issue.

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