Using List<T> causes second Page Load in ASP.Net - asp.net

I have a fairly simple web application that gets a list of items from a database (in a DataTable), and binds a view of that DataTable to a Repeater.
When converting my DataTable to a List (which is done in a class library), Page Load fires a second time! Walking though the debugger, the same items are in the list that were in the DataTable.
The only code in my page was:
protected void Page_Load(object sender, EventArgs e)
{
if (!IsPostBack)
{
rptOffers.DataSource = DataAccess.GetOfferList(offerId); // returns List<T>
rptOffers.DataBind();
}
}
public static List<OfferItem> GetOfferList(int offerId)
{
DataTable dtOffers = GetOfferData(offerId);
List<OfferItem> offers = new List<OfferItem>();
// loop throw all of the offers
foreach (DataRow dr in dtOffers.Rows)
{
// add each offer to the List<>
OfferItem currentOffer = new OfferItem();
// initialize the OfferItem properties...
offers.Add(currentOffer);
}
return offers;
}
When I change it back to this, it works fine:
protected void Page_Load(object sender, EventArgs e)
{
if (!IsPostBack)
{
rptOffers.DataSource = DataAccess.GetOfferItems(offerId);
rptOffers.DataBind();
}
}
Is there anything else I need to do in my List to keep it from running Page Load again?

I have experienced this issue when AutoEventWireup is set to true in my .aspx file
<%# ... AutoEventWireup="True" ... %>
and my InitializeComponent function still contains a hookup for Page_Load
private void InitializeComponent()
{
this.Load += new System.EventHandler(this.Page_Load);
}

Related

Why is my UserControl's ViewState partially saved?

I have a user control that makes substantial use of this.ViewState["Key"] = SomeValue. Most of it is loaded from my Page_Init():
protected void Page_Init(object sender, EventArgs e)
{
if(!IsPostBack)
{
ViewState["Blahblah"] = LoadSomeValue();
}
}
The rest are set at various points.
But for some reason it's unavailable on subsequent postbacks. I overrode SaveViewState() to check, and only like three of them are saved!
protected override object SaveViewState()
{
List<object> viewStateObjectsBefore = ViewState.OfType<object>().ToList();
object ret = base.SaveViewState();
List<object> viewStateObjectsAfter = ViewState.OfType<object>().ToList();
GC.KeepAlive(viewStateObjectsBefore);
GC.KeepAlive(viewStateObjectsAfter);
GC.KeepAlive(ret);
return ret;
}
Both viewStateObjectsBefore and viewStateObjectsAfter contain 10 key/value pairs, but ret only contains three!
Added: Moving the initializations to Page_Load() is not an easily available option, because the initializations must be done before the parent's Page_Load() executes.
Adding a call to SetDirty() at the end of my Page_Init() solved the problem:
protected void Page_Init(object sender, EventArgs e)
{
if(!IsPostBack)
{
ViewState["Blahblah"] = LoadSomeValue();
//Looks like the ViewState is not yet "tracking" changes before Page_Load.
//The items have to be marked as "dirty" manually so they'll be included by SaveViewState().
ViewState.SetDirty(true);
}
}

unable to persist data on postback in dotnetnuke7

I have my website running on dotnetnuke 7.4, i have a checklistbox which i bind on the page load, and after selecting items from it, user clicks on the submit button, the selected items should save in database, however when i click on the submit button, checklistbox gets blank, i tried to enable ViewState at :
Web.config level
Page Level
Control Level
But all in vain, it still unbinds checklistbox because of which everything disappears, i tried the same in plain .net and it works like a charm.
Is there any specific settings in dotnetnuke to support viewstate, or is there any other better option to achieve this.
Here's my code:
protected void Page_Load(object sender, EventArgs e)
{
if (!IsPostBack)
{
Entities objEntities = new Entities();
List<Entities> obj = objEntities.GetList(2);
chkBox.DataSource = obj;
chkBox.DataTextField = "Name";
chkBox.DataValueField = "ID";
chkBox.DataBind();
}
}
protected void btnSubmit_Click(object sender, EventArgs e)
{
foreach (ListItem item in chkBox.Items)
Response.Write(item.Text + "<br />");
}
There's the issue. Remove that (!IsPostBack) check in your page_load event. Have your code to be like below. Else, only at first page load you are binding the datasource to control which gets lost in postback.
protected void Page_Load(object sender, EventArgs e)
{
Entities objEntities = new Entities();
List<Entities> obj = objEntities.GetList(2);
chkBox.DataSource = obj;
chkBox.DataTextField = "Name";
chkBox.DataValueField = "ID";
chkBox.DataBind();
}
OR, to be more efficient; refactor your code to a method like below and store the data object in Session variable like
private void GetDataSource()
{
List<Entities> obj = null;
if(Session["data"] != null)
{
obj = Session["data"] as List<Entities>;
}
else
{
Entities objEntities = new Entities();
obj = objEntities.GetList(2);
}
chkBox.DataSource = obj;
chkBox.DataTextField = "Name";
chkBox.DataValueField = "ID";
chkBox.DataBind();
Session["data"] = obj;
}
Call the method in your Page_Load event like
protected void Page_Load(object sender, EventArgs e)
{
GetDataSource();
}

value of private variable is not maintained after page load even in ASP.NET

I have two pages. first.aspx and second.aspx. In order to get all the control values from first.aspx, i added directive to second.aspx
<%# PreviousPageType VirtualPath="~/PR.aspx" %>
I have no problem to get all the previous page controls and set it to labels, but i have a big problem to save those values to a private variable, and reuse it after page load event is done. Here is code example. when i try to get the value from input in another method, it has nothing added. Why?
public partial class Second : System.Web.UI.Page
{
List<string> input = new List<string>();
protected void Page_Load(object sender, EventArgs e)
{
if (Page.PreviousPage != null&&PreviousPage.IsCrossPagePostBack == true)
{
TextBox SourceTextBox11 (TextBox)Page.PreviousPage.FindControl("TextBox11");
if (SourceTextBox11 != null)
{
Label1.Text = SourceTextBox11.Text;
input.Add(SourceTextBox11.Text);
}
}
}
protected void SubmitBT_Click(object sender, EventArgs e)
{
//do sth with input list<string>
//input has nothing in it here.
}
}
The SubmitBT_Click-click event happens in a postback. But all variables (and controls) are disposed at the end of the page's lifecycle. So you need a way to persist your List, e.g. in the ViewState or Session.
public List<String> Input
{
get
{
if (Session["Input"] == null)
{
Session["Input"] = new List<String>();
}
return (List<String>)Session["Input"];
}
set { Session["Input"] = value; }
}
Nine Options for Managing Persistent User State in Your ASP.NET Application

Viewstate null on postback

So I have a listbox on my page and some textfields. Through the textfields I can add an item to my listbox (click the button, it adds it to a private List which is then set as a ViewState and the list is databound again). My listbox is also in an updatepanel which gets triggered on the button's Click event. Problem: My Viewstate remains null on a postback so it gets reset each time.
Some code:
private const string VIEW_INGREDIENTS = "IngredientsList";
private const string VIEW_LANGUAGE = "CurrentLanguage";
private List<IngredientData> _ingredientsList;
protected void Page_PreInit(object sender, EventArgs e)
{
if (Page.IsPostBack)
{
if (ViewState[VIEW_INGREDIENTS] != null)
{
_ingredientsList = (List<IngredientData>) ViewState[VIEW_INGREDIENTS];
}
}
else
{
// prepare ingredient lists
_ingredientsList = new List<IngredientData>();
}
}
protected void Page_Load(object sender, EventArgs e)
{
lstIngredients.DataSource = _ingredientsList;
lstIngredients.DataTextField = "Text";
lstIngredients.DataValueField = "Name";
lstIngredients.DataBind();
}
protected void btnAddIngredient_Click(object sender, EventArgs e)
{
_ingredientsList.Add(new IngredientData { Name = txtIngredientName.Text, Quantity = txtUnitQuantity.Text, Unit = lstUnits.SelectedValue });
ViewState[VIEW_INGREDIENTS] = _ingredientsList;
lstIngredients.DataSource = _ingredientsList;
lstIngredients.DataBind();
}
You're using vewstate during PreInit ? Try to check that a bit later during PreLoad.
Check if the page has EnableViewState="true":
<%# Page Language="C#" EnableViewState="true" ...
And verify the site-wide setting in web.config:
<pages enableViewState="true" enableViewStateMac="true" ... />
Now ASP.NET has built-in viewstate for list controls, so I wonder why you're writing custom code for it. The default viewstate should work well for what you're trying to accomplish.

Accessing Events And Members In The Master Page

I have an event in the Master page that I want to access in the pages that use that master page but it doesn't seem to be working.
In the Master
public delegate void NotifyRequest(object sender, EventArgs e);
public class MyMaster
{
public event NotifyRequest NewRequest;
protected void uiBtnNewTask_Click(object sender, EventArgs e)
{
if(NewRequest!= null)
NewRequest(this, e)
}
}
Inherited Page
MyMaster mm = new MyyMaster();
mm.NewRequest += new NotifyRequest(mm_NotifyRequest);
void mm_NotifyRequest(object sender, EventArgs e)
{
Label1.Text = "Wow";
this.Label1.Visible = true;
}
My problem is the event is always null. Any ideas?
You probably need to use the following syntax to access your event in the Master Page
((MyMaster)Master).NewRequest += new NotifyRequest(mm_NotifyRequest);
If you wish to access members of a master page you need to use the page Master attribute and cast it to your master page.
Alternately
If you wish do not wish to use a cast you can use the #MasterType directive to create a strong reference to your master page, in this case MyMaster. So you would be able to access your event like so: Master.NewRequest.
More Reading about Master Pages

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