We Keep Coding

ASP.NET Session State & Postback problems

I have a problem that I believe is a session state issue, but I'm at a loss to figure out what's wrong. I have a sample project to illustrate the problem. (Code below) I have 2 buttons. Each populates a List with some unique data and then uses that data to add a row to a table. The row contains text boxes so that the user can edit the data. (For my sample, there's no update button to persist the data.) To reproduce the problem in VS2010, create a new "ASP.NET Web Application" project and copy/paste the aspx code and the c# code-behind into Default.aspx, then run the application.
Press the DataSet 1 button and the grid should populate with 1 row.
Edit the data in one of the text boxes and tab off of the text box. (The newly entered text should remian, and the font should be blue. This is what I want to happen.)
Now click either of the DataSet buttons to reset the List and refresh the table.
Edit the data in one of the text boxes and tab off the text box. (Immediately, the text in the box refreshes back to its original value. This only happens once, though. If you edit either text box now, it will work normally.)
This is repeatable... the first edit after pressing the DataSet buttons a 2nd, 3rd, etc. time gets reset back to the original value. And I can't figure out why.
<%# Page Title="Home Page" Language="C#" MasterPageFile="~/Site.master" AutoEventWireup="true"
CodeBehind="Default.aspx.cs" Inherits="DebugPostbackIssue._Default" %>
<asp:Content ID="HeaderContent" runat="server" ContentPlaceHolderID="HeadContent">
</asp:Content>
<asp:Content ID="BodyContent" runat="server" ContentPlaceHolderID="MainContent">
<h2>
Welcome to ASP.NET!
</h2>
<p>
Populate the table with DataSet #1:<asp:Button runat="server" ID="btnDS1" Text="Dataset 1" OnClick="btnDS1_Click" />
</p>
<p>
Populate the table with DataSet #2:<asp:Button runat="server" ID="btnDS2" Text="Dataset 2" OnClick="btnDS2_Click" />
</p>
<p>
<asp:Table runat="server" ID="tblData">
<asp:TableHeaderRow runat="server" ID="thrData">
<asp:TableHeaderCell Scope="Column" Text="Column 1"></asp:TableHeaderCell>
<asp:TableHeaderCell Scope="Column" Text="Column 2"></asp:TableHeaderCell>
</asp:TableHeaderRow>
</asp:Table>
</p>
</asp:Content>
using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
namespace DebugPostbackIssue
{
public partial class _Default : System.Web.UI.Page
{
private List<string> _MyData = new List<string>();
protected void Page_Load(object sender, EventArgs e)
{
}
protected void Page_Init(object sender, EventArgs e)
{
LoadSessionData();
GenerateGrid(false);
}
protected void btnDS1_Click(object sender, EventArgs e)
{
_MyData = new List<string>();
_MyData.Add("111");
_MyData.Add("aaa");
SaveSessionData();
GenerateGrid(true);
}
protected void btnDS2_Click(object sender, EventArgs e)
{
_MyData = new List<string>();
_MyData.Add("222");
_MyData.Add("bbb");
SaveSessionData();
GenerateGrid(true);
}
private void SaveSessionData()
{
Session["MyData"] = _MyData;
}
private void LoadSessionData()
{
if (Session["MyData"] != null)
_MyData = (List<string>)Session["MyData"];
else
_MyData = new List<string>();
}
private void GenerateGrid(bool ClearData)
{
if (ClearData)
while (tblData.Rows.Count > 1)
tblData.Rows.Remove(tblData.Rows[tblData.Rows.Count - 1]);
TableRow tr = new TableRow();
foreach (string s in _MyData)
{
TableCell tc = new TableCell();
TextBox txtBox = new TextBox();
txtBox.Text = s;
txtBox.Attributes.Add("OriginalValue", s);
txtBox.TextChanged += new EventHandler(txtBox_TextChanged);
txtBox.AutoPostBack = true;
tc.Controls.Add(txtBox);
tr.Cells.Add(tc);
}
if (tr.Cells.Count > 0)
tblData.Rows.Add(tr);
}
void txtBox_TextChanged(object sender, EventArgs e)
{
TextBox Sender = (TextBox)sender;
if (Sender.Text == Sender.Attributes["OriginalValue"])
Sender.ForeColor = System.Drawing.Color.Black;
else
Sender.ForeColor = System.Drawing.Color.Blue;
}
}
}

Hi I took some time off of my work to compile your code, and I figured it out, just change your textbox change to the following :
void txtBox_TextChanged(object sender, EventArgs e)
{
TextBox Sender = (TextBox)sender;
if (Sender.Text == Sender.Attributes["OriginalValue"])
Sender.ForeColor = System.Drawing.Color.Black;
else
{
Sender.ForeColor = System.Drawing.Color.Blue;
if (Session["MyData"] != null)
{
List<string> _ss = (List<string>)Session["MyData"];
//_ss.Find(a => a == Sender.Attributes["OriginalValue"]);
_ss.Remove(Sender.Attributes["OriginalValue"]);
_ss.Add(Sender.Text);
}
}
}
ur welcome!

Try creating a datatable. I would, on "event" copy your asp table content to a datatable, then when you get the servers response add that to the datatable. Then copy the datatable back to your asp table, and repeat... Datatables can be used like variables.
Or try using a cookie.

Try changing...
protected void Page_Init(object sender, EventArgs e)
{
LoadSessionData();
GenerateGrid(false);
}
To...
protected override void OnLoadComplete(EventArgs e)
{
LoadSessionData();
GenerateGrid(false);
}
Based on your description I believe that your value is getting reset because of how the page life cycle works in ASP.NET & that is the page_init is getting called before your event due to ASP.NET quirkiness. Above code is how I work around it, I'm sure there's other ways too.

Okay, I have it working, now. Wizpert's answer pointed me in the right direction... Upon discovering that the TextChanged event did not fire during the times when the value was erroneously being reset to the original value, it occurred to me that during the Click events I was calling GenerateGrid(true). This forced the removal of the existing rows and the addition of new rows. (Removing & adding the dynamic controls at that point in the life cycle must be interfering with the TextChange event handler.) Since the Click event fires after Page Init and after Page Load, the state values were already written to the text boxes and I was overwriting them. But the 2nd text box edit did not force GenerateGrid(true) to be called so the state values were not overwritten any more.
If this sounds confusing, I apologize. I'm still wrapping my head around this. But suffice to say that I had to change my GenerateGrid method to reuse any existing rows and not delete them. (If they don't exist, like when GenerateGrid is called from Page Init, then they are added.) So this was a page lifecycle issue after all.
Thank you.

Manually bind a row in a repeater, to avoid losing viewstate data

I'm working on a page that uses a repeater to display a list of custom controls, each containing two dropdown lists.
On a click on the Add control button, the page adds a new row on the repeater, and a click on one of the Delete control buttons embedded in each control removes the relevant control from the repeater.
The delete part seems to work, (setting NamingController.Visible to false), but the add part fails, as once I add the new control, a call to a new repeater.DataBind() loses all viewstate data, preventing the dropdownlists from retrieving the values they had before postback.
Is there a way to manually bind the added control to the repeater without calling a full databind ? Or is there any other way to add a control without losing data ?
Here's some code (I only left what seems relevant, please let me know if you think I forgot to specify something) :
Page.aspx:
<asp:Button ID="addControl" runat="server" Text="Add control" />
<asp:Repeater ID="repeater" runat="server" OnItemDataBound="repeater_ItemDataBound">
<ItemTemplate>
<uc:CustomControlWithDropDownLists ID="custom" runat="server" />
</ItemTemplate>
</asp:Repeater>
Page.aspx.cs:
protected override void OnInit(EventArgs e)
{
base.OnInit(e);
repeater.DataSource = GetDataSource();
repeater.DataBind();
}
protected void Page_Init(object sender, EventArgs e)
{
addControl.Click += (sndr, args) =>
{
// Create the object we want to bind to the repeater
ObjectToBind objectToBind = new ObjectToBind();
// Here is what causes data loss
((IList<ObjectToBind>)repeater.DataSource).Add(objectToBind);
repeater.DataBind();
};
}
protected void repeater_ItemDataBound(object sender, RepeaterItemEventArgs e)
{
if (e.Item.ItemType == ListItemType.Item || e.Item.ItemType == ListItemType.AlternatingItem)
{
// Do some stuff
}
}
CustomControlWithDropDownLists.ascx:
<%-- Some dropdown lists --%>
<asp:Button ID="deleteControl" runat="server" Text="Delete control" />
CustomControlWithDropDownLists.ascx.cs:
protected void Page_Init(object sender, EventArgs e)
{
deleteControl.Click += (sndr, args) =>
{
// ... Delete the control ...
((Button)sndr).NamingContainer.Visible = false;
};
}

You are loosing the data because of View state.
View State losses the data when we are redirecting to the another page.
View state only store the data for the specific page.
The moment you go to another page data is lost by view state.
& there are many chances of losing the data on the same page because of many reasons.
So, the best way to store the data is to use session variable.
Session stores the data even when you are redirecting to the another page.
It is the best way to store the data.
By default it stores the data for 20 minutes.
I hope this will solve your issue.

I had done something similar in the past and found this link from c-sharp corner helpful.
http://www.c-sharpcorner.com/Blogs/10913/add-dynamic-row-using-repeater.aspx
The key element for me if memory servers is using the ViewState object and binding accordingly.
myObject = ViewState["MyData"]; etc.
( I am sorry I don't have access to my code at the moment )

Retrieving MasterPage textbox Control on a postback to another page

I have spend two days trying to figure out the solution to this problem, even tried ExpertExchange and still I can't get a solution. I am a very novice programmer to ASP.Net (using C#) and I DON'T want to use a string/url post
I have a MasterPage of which has a textbox called tbSearchString. It is a simple box that a user can enter something and then it does a Postback to another page SearchResults.aspx So I also have other pages, like Default.aspx that uses the MasterPage.
I have tried nearly everything and have read nearly every post I could find on the net and no mater what the Variables are always Null.
I have use this code on the searchResults loadpage event and Every one of these variables are null, even though I enter a value in the page text box and click the button to postback to the SearchResults page, the only time it works is if I am on the searchResults page and submit.
SearchResults back end page
protected void Page_Load(object sender, EventArgs e)
{
TextBox SearchString;
TextBox SearchString2;
TextBox SearchString3;
TextBox SearchString5;
if (Page.PreviousPage != null) //This is true on every test
{
SearchString = (TextBox)Page.PreviousPage.Master.FindControl("tbSearchString");
SearchString2 = (TextBox)PreviousPage.Master.FindControl("tbSearchString");
SearchString3 = (TextBox)Master.FindControl("tbSearchString");
TextBox LoginControlx = (TextBox)PreviousPage.FindControl("Form1");
if (LoginControlx != null)
{
TextBox SearchString4 = (TextBox)LoginControlx.FindControl("tbSearchString");
}
}
MainWebsite.Master page Code
<asp:TextBox ID="tbSearchString" runat="server"></asp:TextBox>
<asp:Button ID="btnSearch1" runat="server" Text="Search" PostBackUrl="~/SearchResultRentalEquiptment.aspx" />
I don't have anything in the CS backend page
So on the Default.aspx page
nothing special Just the Masterpage and some text content, I enter some text in the textbox goes to the SearchResults page and I can not get the darn value from the Textbox control from the Default or any other page.
What say you wise ones?

how do you redirect your form to search result form? if you are using Response.redirect, the value under Page.PreviousPage.Master.FindControl will be null . Try to use Server.Transfer to see if it works.

Here's one way:
Assuming this is your Master Page code:
<asp:TextBox ID="searchbox" runat="server" /><br />
<asp:Button ID="sendSearch" runat="server" PostBackUrl="~/Results.aspx" Text="Search" />
At the end of the day, it's all about HTTP POST, so in the target page Results.aspx PageLoad:
protected void Page_Load(object sender, EventArgs e)
{
string _foo = Request.Form[this.Master.FindControl("searchbox").UniqueID];
}
Hth....

Check out Session. I use it all the time when I need to get data from one page to another. I'm not currently able to write out a full example for you, but off the top of my head the following should work:
//page1.aspx:
protected void btnSubmit_Click(object sender, EventArgs e)
{
string greetingString = "Hello";
Session["MyValue"] = greetingString;
Response.Redirect("page2.aspx");
}
//page2.aspx:
protected void Page_Load(object sender, EventArgs e)
{
Response.Write(Session["MyValue"].ToString()); //prints "Hello"
}

On Postback, the DataTable data source for a Repeater is empty?

Background
I have a User Control (an .ascx file) which is being dynamically inserting into an asp:PlaceHolder control on a page. That User Control contains an asp:Repeater, which I'm binding to a DataTable.
Theoretically, on the User Control's first load the DataTable is initialized and 3 empty rows are added. A button on the User Control adds additional empty rows to the Repeater, one at a time.
Problem
The issue is that after any PostBack event on the page (namely the button in this example being clicked), the DataTable for the Repeater is empty.
User Control (.ascx)
(simplified)
<asp:TextBox ID="controlOutsideRepeater" runat="server" />
<asp:Repeater ID="myRepeater" runat="server">
<ItemTemplate>
<p><asp:Textbox ID="firstControlInRepeater" runat="server" text='<%# DataBinder.Eval(Container.DataItem, "A") %>' /></p>
<p><asp:Textbox ID="secondControlInRepeater" runat="server" text='<%# DataBinder.Eval(Container.DataItem, "B") %>' /></p>
</ItemTemplate>
</asp:Repeater>
<asp:LinkButton ID="addItemButton" runat="server" Text="Add Item" onclick="addNewItem" />
Code Behind (.ascx.cs)
(also simplified)
public DataTable items {
get {
object i = ViewState["items"];
if (i == null) {
DataTable t = new DataTable();
t.Columns.Add("A");
t.Columns.Add("B");
// add 3 blank items/rows:
t.Rows.Add(t.NewRow());
t.Rows.Add(t.NewRow());
t.Rows.Add(t.NewRow());
ViewState["items"] = t;
return t;
} else {
return (DataTable)i;
}
set { ViewState["items"] = value; }
}
protected void Page_Init(object sender, EventArgs e) {
myRepeater.DataSource = this.items;
myRepeater.DataBind();
}
public void addNewItem(object sender, EventArgs e) {
DataRow r = this.items.NewRow();
this.items.Rows.Add(r);
myRepeater.DataBind();
}
Behavior
The first time the UserControl is loaded, the Repeater contains 3 empty items: good! However, after entering some text in the textboxes both inside and outside the repeater and clicking the "Add Item" LinkButton, the page does a refresh/postback and shows 4 empty items, however the textbox -outside- the Repeater retains it's text. Clicking the "Add Item" LinkButton again also performs a postback and still shows 4 empty items, yet the TextBox outside the Repeater again retains it's text.
My Crazy Guess
I've tried wrapping the Repeater databinding in a (!Page.IsPostBack), but this prevented the Repeater from -ever- being bound, as the UserControl is only programmatically added to the page after a PostBack (a button on the Page adds the UserControl on a click, and then the Page checks each PostBack to see if there should be a user control present and re-adds it to the Page if needed). So I'm guessing there's a problem with the Page re-creating the User Control on every PostBack, but can't explain why the TextBox outside the Repeater would retain it's value, and why the ViewState doesn't seem to remember my item (on each postback ViewState["items"] is null and gets re-built within the getter).
HELP!

The problem is you are data binding every single request when really you only want to data bind on the first request. Since you don't data bind on the first page load, you will have to check if you are data bound in a way other than !Page.IsPostBack. You could add a property to your user control to handle this and then check against that every page load / page init.
Update: With more details from comments
I see your AddItem() now. I've had problems using viewstate this way though I'm not entirely sure why. I've had to do it more like the following:
public void addNewItem(object sender, EventArgs e) {
DataTable theItems = this.items;
DataRow r = theItems.NewRow()
theItems.Rows.Add(r);
this.items = theItems
myRepeater.DataBind(); //I'm not sure if this belongs here because of the reasons said before
}

ASP.NET ListView-embedded Web-Control loses state and passed-values on ItemDataBound event handler when page posts back

This question is about a very strange behavior of web controls. Consider the following please.
Scenario
I have a web control which is used to show some data. MyWebControl.ascx file is the following:
<%# Control ViewStateMode="Enabled"
Language="C#"
AutoEventWireup="true"
CodeFile="MyWebControl.ascx.cs"
Inherits="MyWebControl" %>
<div>
<asp:Label ID="MyLabel1" runat="server"></asp:Label>
<asp:Label ID="MyLabel2" runat="server"></asp:Label>
</div>
And code behind MyWebControl.ascx.cs is:
public partial class MyWebControl :
System.Web.UI.UserControl {
protected string str1;
protected string str2;
public string Str1 {
get { return this.str1; }
set { this.str1 = value; }
}
public string Str2 {
get { return this.str2; }
set { this.str2 = value; }
}
protected void Page_Load(object sender, EventArgs e) {
this.MyLabel1.Text = this.str1;
this.MyLabel2.Text = this.str2;
}
}
Well, I use this control inside a ListView of mine in an ordinary web form. This web form is called Default.aspx and, following, I am showing a slice of its code, only the one where the ListView resides in:
<%# Page Title="My page" Language="C#" AutoEventWireup="true"
CodeFile="Default.aspx.cs" Inherits="_Default" %>
<%# Register TagPrefix="my" TagName="MyWC" Src="~/MyWebControl.ascx" %>
...
...
<div>
<asp:ListView ID="MyLV_ListView" runat="server"
EnableViewState="true"
OnPreRender="MyLV_ListView_PreRender"
OnItemDataBound="MyLV_ListView_ItemDataBound">
<ItemTemplate>
<my:MyWC ID="WC_MyWC" runat="server" />
</ItemTemplate>
</asp:ListView>
</div>
This web form code-behind Default.aspx.cs is:
public partial class _Default : System.Web.UI.Page {
protected void Page_Load(object sender, EventArgs e) {
if (!this.IsPostBack) {
DAO d = new DAO(...); /* This object will contain some data */
/* Data are somehow paged, changing index, we have other data */
/* Please do not worry about paging, it works, problem is another */
d.PageIndex = 0;
this.ViewState["DAO"] = d; /* DAO is serializable */
this.ViewState["PageIndex"] = 0;
Data[] data = d.GetData(); /* Returns an array of objects representing my data */
/* Custom way of storing data in objects */
/* GetData use the PageIndex to get only a range of results */
this.MyLV_ListView.DataSource = data;
this.MyLV_ListView.DataBind();
}
}
protected void MyLV_ListView_ItemDataBound(object sender, ListViewItemEventArgs e) {
if (e.Item.ItemType == ListViewItemType.DataItem) {
((MyWebControl)e.Item.FindControl("WC_MyWC")).Str1 =
((Data)e.Item.DataItem).DataField1;
((MyWebControl)e.Item.FindControl("WC_MyWC")).Str2 =
((Data)e.Item.DataItem).DataField2;
}
}
protected void MyLV_ListView_PreRender(object sender, EventArgs e) {
if (this.IsPostBack)
this.MyLV_ListView.DataBind();
}
// A TreeView will cause the page to reload,
// this is the handler called when a tree node is
// selected, the node is used to change the page
// for showing data in my listview.
protected void MyLVPaging_TreeView_SelectedNodeChanged(object sender, EventArgs e) {
this.ViewState["PageIndex"] = int.Parse(this.MyLVPaging_TreeView.SelectedNode.Value);
((DAO)this.ViewState["DAO"]).PageIndex = (int)this.ViewState["PageIndex"];
// After setting the new index, GetData will return another set of results
this.MyLV_ListView.DataSource = ((DAO)this.ViewState["DAO"]).GetData();
}
}
The problem
What is my problem???
Well, when the page loads for the first time I can see some data in the list view, so everything works.
When I select another page, I cause the page to reload and post back... my ListView will show the correct number of entries but with no data in it. The web control is placed as many times as the number of retrieved data records, but the web control has no data in it.
Debugging results
I conducted some debug sessions and this is what happens, please follow me, this is VERY IMPORTANT to understand I guess.
Page loads for the first time
1) Load page method is executed.
2) ListView's ItemDataBound event handler is executed. Well, given that I have three elements in the Data[] array in the DataSource, the handler is called three times. Inspecting values when proceeding debugging the method, I can see that ((Data)e.Item.DataItem).DataField1 and ((Data)e.Item.DataItem).DataField2 are the correct values retrieved from the bound data source in the ListView.
After the method is executed, the debugger cursor moves to MyWebControl.ascx.cs to the control's Page_Load method. I can see, inspecting variables, that this happens:
protected void Page_Load(object sender, EventArgs e) {
this.MyLabel1.Text = this.str1; // <-- this.str1 has the correct value loaded in the list view itemdatabound event handler.
this.MyLabel2.Text = this.str2; // <-- this.str2 has the correct value loaded in the list view itemdatabound event handler.
}
3) The ListView PreRender method is called.
4) The page shows and everyting is ok!
Page posts back after selecting a node in the TreeView
1) Load page method is executed but it does nothing.
2) MyLVPaging_TreeView_SelectedNodeChanged is executed. Here I can see that everything has the correct value:
protected void MyLVPaging_TreeView_SelectedNodeChanged(object sender, EventArgs e) {
this.ViewState["PageIndex"] =
int.Parse(this.MyLVPaging_TreeView.SelectedNode.Value); // <-- The new page
((DAO)this.ViewState["DAO"]).PageIndex =
(int)this.ViewState["PageIndex"]; // <-- Index saved
// After setting the new index, GetData will return another set of results
this.MyLV_ListView.DataSource =
((DAO)this.ViewState["DAO"]).GetData(); // <-- DataSource is changed
}
3) ListView's ItemDataBound event handler is executed. Well, here, debugging I can see the same as before, I mean, I can see that new values, new Data have been bound to the ListView, in fact I can inspect new values that are assigned to the template item.
Obviously, as before, after the method is executed, the debugger cursor moves to MyWebControl.ascx.cs to the control's Page_Load method.
HERE IS EVIL: I can see the following:
protected void Page_Load(object sender, EventArgs e) {
// Note: inspecting this.IsPostBack I get true!
this.MyLabel1.Text = this.str1; // <-- this.str1 is null and also this.MyLabel1.Text is null.
this.MyLabel2.Text = this.str2; // <-- this.str2 is null and also this.MyLabel1.Text is null. view itemdatabound event handler.
}
Well!!! IT LOSES STATE AND ALSO VALUES
PASSED BY THE LIST VIEW
HANDLER!!!!!!!!!
My question
What the hell is going on???
Notes
1) Please, do not focus too much on how I managed data binding on Load and PreRender events... I have a feeling this is not the error! I guess it is something related to the page lifecycle. However, if you think that this is important detail, let me know.
2) DAO and its function GetData() are a way to let you understand as quick as possible the scenario which is a little bit more articulated, but with the same exact structure I've shown here.
Thank you for your help.

From my comments:
Why don't you move the
this.MyLV_ListView.DataBind() from
PreRender to SelectedNodeChanged? And
why do you need the fields str1 and
str2 in your UserControl? The property
Str1 should get/set this.MyLabel1.Text
and the property Str2should get/set
this.MyLabel2.Text, because the
lables' Text are already stored in
ViewState.
Andry:
... so these kind of settings are not
to be made in the Load?
Me:
you don't need to wait for any event
to happen to set the label's text. The
properties should directly lead to the
corresponding Labels, hence your
fields str1 and str2 are redundant.
They will be disposed at the end of
the Page-Lifecycle as opposed to the
Text property of the Labels which are
stored in ViewState automatically
across postbacks.