I'm trying to understand the phases of an asp.net page lifecycle by building a simple site web composed of a web form with a code behind in c#.
In the aspx page there is only a button to make a postback so I won't show the code; instead, I'll report the browser output because I use the Response.Write method to write all the page phases that I'm handling.
In the aspx.cs file I started the class with a property:
public string prop
{
get
{
object _propViewstate = ViewState["propview"];
if (_propViewstate != null)
{
return (string)_propViewstate;
}
else
{
return "Prop ViewState still not avaiable <BR> ";
}
}
set
{
ViewState["propview"] = value;
}
}
How you can see it's used to store in the ViewState a string value that I'll check in each phase. The setting of the property becomes in the method that handles the PreInit event of Page only if it's not a postback (I take advantage of AutoEventWireUp):
protected void Page_PreInit(object sender, EventArgs e)
{
Response.Write("PreInit_Method <BR>");
if (!Page.IsPostBack)
{
prop = "PreInit";
}
Response.Write(prop + "<BR> <BR>");
}
Then I'll override these methods of the Page to check this property in the ViewState: OnInit, OnInitComplete, OnPreLoad, OnLoad, OnLoadComplete. The code is very similar so I'll show only the OnInit override:
protected void Page_Init(object sender, EventArgs e)
{
Response.Write("Init_Method <BR>");
if (!Page.IsPostBack)
{
prop += " - Init";
}
Response.Write(prop + "<BR> <BR>");
}
I update the value of the property in the ViewState for each method if it's not a postback. I override also the LoadViewState method:
protected override void LoadViewState(object savedState)
{
Response.Write("LoadViewState_Method <BR>");
Response.Write("Before calling base method: ");
Response.Write(prop);
base.LoadViewState(savedState);
Response.Write("After calling base method: ");
Response.Write(prop + "<BR> <BR>");
}
Now I show the output before and after the postback and then finally my questions will come:
Without PostBack
After PostBack
My questions:
0) First of all, I'm using those methods correctly to test the loading of the ViewState? Which would be a better way to test it?
1) Before to PostBack, the property is available in all the methods. This is because I'm accessing to this viewstate's property that I just created? (If I do Response.Write(ViewState["propview"] + "<BR> <BR>"); I got the same effect, obviously)
2) Based on my test, I could say that the ViewState is loaded in the LoadViewState method because before to call the parent's method inside it I can't see my property set but just after that call it's available.
On the net, I read that the ViewState is instead loaded on LoadPageStateFromPerstistenceMedium. In the image from the official ASP.NET Page Life Cycle, I see that LoadPageStateFromPerstistenceMedium is called before LoadViewState and with my test inside this method I checked that my property is not available before the call to base.LoadViewState so I would say that the ViewState is loaded in the Page's LoadViewState method, correct?
Related
The scenario is very simple. I have an aspx page with a user control. I want to set a value and get a response from usercontrol on aspx page's pageload. The SET job is done, but can't GET the response. It's always empty. I tried two methods, but none of them worked.
ASPX PAGE
<uc1:ucContent ID="Content1" runat="server" />
CODE BEHIND
protected void Page_Load(object sender, EventArgs e)
{
// SET job is working without any problem
Content1.ItemName = "X";
//METHOD ONE:
Page.Title = Content1.MetaPageTitle;
//METHOD TWO:
HiddenField hdnPageTitle = (HiddenField)Content1.FindControl("hdnMetaPageTitle");
Page.Title = hdnPageTitle.Value;
}
USER CONTROL
protected void Page_Load(object sender, EventArgs e)
{
if (string.IsNullOrEmpty(itemName))
{
// GET DATA FROM DB
// METHOD ONE:
hdnTitle.Value = DB.DATA;
// METHOD TWO:
metaPageTitle = DB.DATA;
}
}
private string metaPageTitle;
public string MetaPageTitle
{
// METHOD ONE:
get { return metaPageTitle; }
// METHOD TWO:
get { return hdnTitle.value; }
}
EDIT
itemName is a UserControl property to get a value from Parent Page:
private string itemName;
public string ItemName
{
set { itemName = value; }
}
Thanks for your kind help in advance!
I think that the problem is that the page's Page_Load is triggered before the UserControl(Have a look: asp.net: what's the page life cycle order of a control/page compared to a user contorl inside it?).
So you could set the property in Page_init:
In your UserControl:
protected void Page_Init(object sender, EventArgs e)
{
if (string.IsNullOrEmpty(itemName))
{
// GET DATA FROM DB
hdnTitle.Value = DB.DATA;
}
}
Now this should work in your page's Page_Load:
Page.Title = Content1.MetaPageTitle;
Normally i would prefer another kind of communication between a Page and a UserControl. It's called event-driven communication and means that you should trigger a custom event in your UC when the MetaPageTitle changed (so in the appopriate event-handler).
Then the page can handle this specific event and react accordingly.
Mastering Page-UserControl Communication - event driven communication
Having just added a new button in my web application, I get an error when clicking on it, and I'm wondering if this is related to misplaced code. I will describe what/where I did, briefly. Thanks very much.
In ascx file:
<asp:Button ID="btn_rezerv" runat="server" Text="Reserve film" OnClick="btn_rezerv_Click"/>
In the ascx.cs file:
namespace CinProj.UserControls
{
public partial class FilmsList : System.Web.UI.UserControl
{
protected void Page_Load(object sender, EventArgs e)
{
PopulateControls();
}
private void PopulateControls()
{
string categId = Request.QueryString["CategID"];
string filmId = Request.QueryString["FilmID"];
....
if (categId != null)
{
.....
}
if (filmId != null)
{
......
Button btn_rezerv = (Button)item.FindControl("btn_rezerv");
}
}
protected void btn_rezerv_Click(object sender, EventArgs e)
{
string fid = Request.QueryString["FilmID"];
ShoppingCartAccess.AddItem(fid);
}
}
}
"Server Error in '/' Application.
Invalid postback or callback argument. Event validation is enabled using in configuration or <%# Page EnableEventValidation="true" %> in a page. For security purposes, this feature verifies that arguments to postback or callback events originate from the server control that originally rendered them. If the data is valid and expected, use the ClientScriptManager.RegisterForEventValidation method in order to register the postback or callback data for validation. "
Another problem could be because your PopulateControls method should probably only be called when during the Page Load when it's not a PostBack. I can't tell from above, but to me it looks like it only needs done on Load. Try wrapping that call with this:
protected void Page_Load(object sender, EventArgs e)
{
if (!Page.IsPostBack)
{
PopulateControls();
}
}
It's likely the result of making some sort of client change that the server doesn't know about. Many times this is the result of changing values in a dropdown in JavaScript, for example.
To fix, you could:
Do away with using JavaScript for said modification
Use an UpdatePanel and add your control to it. If the client needs to make a change, trigger the UpdatePanel's update in order for the control's viewstate to update.
In my master page, I'm loading a variable in the session like this:
public partial class TheMasterPage : System.Web.UI.MasterPage
{
protected void Page_Load(object sender, EventArgs e)
{
if (!Page.IsPostBack)
{
ViewUserPreferences SessionUserPreferences = new ViewUserPreferences();
SessionUserPreferences = UserPreferences.GetUserPreferencesFromDB(6);
}
}
}
Then, in the code behind of a file, I have this:
protected void Page_Load(object sender, EventArgs e)
{
if (!Page.IsPostBack)
{
var test = Session["SessionUserPreferences"];
}
}
But when I debug, test is null. What's causing the problem?
Also, if I put a break point in the master page, it doesn't trigger when I run the aspx page; is this normal?
Thanks.
First thing you are missing the assignment part for UserPreferences.GetUserPreferencesFromDB(6) to the Session object. (I read the comments for #Greg's answer and you mentioned that even after that it is not working.)
Second, Master Page's Page_Load Event is triggered after the Current Page's Page_Load Event, hence the value of Session["SessionUserPreferences"] is null in Current Page's Page Load event since it is not set yet.
Check this link for further information on Page Events:
http://msdn.microsoft.com/en-us/library/dct97kc3.aspx
You have to do Session["SessionUserPreferences"] = something; somewhere before you attempt to retrieve that. Are you setting it somewhere else that you didn't show?
I have a problem with a webform.
My Goal: Intially when a page is loading, it has to load every textbox empty. After filling the info and click submit, it has to get submitted(UpdatePaymentInfo())
Problem: Here, When the user fills the info and clicks Submit,it calls onload function even before the submit button and makes all text box empty.
Here is the code:
protected override void OnLoad(EventArgs e)
{
base.OnLoad(e);
string QueryStringupdatecreditcard1 = Request.QueryString.ToString();
if (String.Equals(QueryStringupdatecreditcard1, "tabID=B"))
{
divTitle.Visible = false;
trmain.Visible = false;
tdOrderSummary.Visible = false;
trCCandBilling.Visible = true;
trtest2.Visible = false;
divUpdatecreditcard.Visible = true;
trusecompaddress.Visible = false;
txtFirstName.Text = "";
txtLastName.Text = "";
txtAddress1.Text = "";
txtAddress2.Text = "";
txtCity.Text = "";
txtZip.Text = "";
txtCardNo.Text = "";
txtVccNumber.Text = "";
trAmountCharged.Visible = false;
}
}
protected void imgbtnSubmit_Click(object sender, ImageClickEventArgs e)
{
try
{
UpdatePaymentInfo();
}
}
Wrap the current contents of your OnLoad method in:
if (!Page.IsPostBack)
{
// Code in here will only be executed when the page is *not* being loaded by a postback
}
This is because, as per the ASP.NET Page Life Cyle, the things that you care about in this instance happen in this order:
Load - During load, if the current request is a postback, control
properties are loaded with information
recovered from view state and control
state.
Postback event handling - If the request is a postback, control event
handlers are called. After that, the
Validate method of all validator
controls is called, which sets the
IsValid property of individual
validator controls and of the page.
So what happens is (somewhat simplified):
You click the image button, triggering the postback.
The data from your form is loaded into your controls.
Your OnLoad method overwrites the values in the controls to clear them.
Your click handler is run, but because of step 3 it sees empty values.
As others have sort-of mentioned, it wouldn't necessarily be a bad thing to refactor your OnLoad method whilst you're doing this. At the moment you seem to have it doing two distinct things:
Clearing the text fields
Setting the visibility of fields
It might be worth separating this into one or two (depending on if the visibility setting and field clearing will be done independently) separate methods and adjusting your OnLoad method so it looks like this:
protected override void OnLoad(EventArgs e)
{
base.OnLoad(e);
if (!Page.IsInPostBack)
{
SetFieldVisibility();
ClearFields();
}
}
Page_Load always occurs.
See the documentation on the Page Lifecycle
What you need to do is check to see if the Page_Load is being triggered by a Postback.
private void Page_Load(object sender, System.EventArgs e)
{
if(!Page.IsPostBack)
{
///do stuff in here that you want to occur only on the first lad.
}
else
}
// code that you want to execute only if this IS a postback here.
{
}
// do stuff you want to do on Page_Load regardless of postback here.
}
You can use the IsPostBack property of the Page as follows:
protected override void OnLoad(EventArgs e) {
if (!Page.IsPostBack) {
EmptyTextBoxes();
}
}
Have you tried wrapping the form reset code in a check to see if the page is a postback?
if(!Page.IsPostback) {
// Do form reset here
}
You thought about using the IsPostBack page variable?
protected override void OnLoad(EventArgs e)
{
if(!IsPostBack){
//all your logic here.
}
}
if it's the case, you might use a databound control and set it to insert mode
Is it recommended to check the Page.IsPostBack in a user control Page_Load Event like
protected void Page_Load(object sender, EventArgs e)
{
if (!Page.IsPostBack)
{
}
}
I am getting wierd results
Edit ~ Here is the thing. When the main form is loaded, I use Request.QueryString to get the customer id which I then place in a SESSION variable.
On the control Load event I read the SESSION variable to get the data for that customer. So, do I need to check PostBack at the control level?
Edit ~ Here is the load event of the control
protected void Page_Load(object sender, EventArgs e)
{
if (!Page.IsPostBack)
{
//Getting and storing the customer account number
if (string.IsNullOrEmpty((string)Session["CustomerNumber"]))
{
Session["CustomerNumber"] = cust.GetCustomerNumber(myHelper.GetCustomerIDFromQueryString());
LoadProductData();
}
}
}
Here is the myHelper Class
static class myHelper
{
public static Guid GetCustomerIDFromQueryString()
{
//Getting the GUID (used as customerid in CRM) from the URL request of the selected account.
return Sql.ToGuid(System.Web.HttpContext.Current.Request["ID"]);
}
}
}
If you use "!IsPostBack" in page load, when the user click other control it do a postBack, so you don't get your data.
I hope that helps you.
Just checking it for no reason? Absolutely not. If you should do something only on first load and not on subsequent post backs then it's the pattern that should be used.
Are you sure that you will always have a "CustomerNumber" already stored in the Session by the time you get to your page? Is there any rhyme or reason that you can find as to when you get data and when you don't?