Programmatically add UserControl with events - asp.net

I need to add multiple user controls to a panel for further editing of the contained data. My user control contains some panels, dropdown lists and input elements, which are populated in the user control's Page_Load event.
protected void Page_Load(object sender, EventArgs e)
{
// populate comparer ddl from enum
string[] enumNames = Enum.GetNames(typeof (SearchComparision));
var al = new ArrayList();
for (int i = 0; i < enumNames.Length; i++)
al.Add(new {Value = i, Name = enumNames[i]});
scOperatorSelection.DataValueField = "Value";
scOperatorSelection.DataTextField = "Name";
...
The data to be displayed is added to the user control as a Field, defined above Page_Load. The signature of the events is the following:
public delegate void ControlStateChanged(object sender, SearchCriteriaEventArgs eventArgs);
public event ControlStateChanged ItemUpdated;
public event ControlStateChanged ItemRemoved;
public event ControlStateChanged ItemAdded;
The update button on the user control triggers the following method:
protected void UpdateCriteria(object sender, EventArgs e)
{
var searchCritCtl = (SearchCriteria) sender;
var scEArgs = new SearchCriteriaEventArgs
{
TargetCriteria = searchCritCtl.CurrentCriteria.CriteriaId,
SearchComparision = ParseCurrentComparer(searchCritCtl.scOperatorSelection.SelectedValue),
SearchField = searchCritCtl.scFieldSelection.SelectedValue,
SearchValue = searchCritCtl.scFilterValue.Text,
ClickTarget = SearchCriteriaClickTarget.Update
};
if (ItemUpdated != null)
ItemUpdated(this, scEArgs);
}
The rendering page fetches the data objects from a storage backend and displays it in it's Page_Load event. This is the point where it starts getting tricky: i connect to the custom events!
int idIt = 0;
foreach (var item in _currentSearch.Items)
{
SearchCriteria sc = (SearchCriteria)LoadControl("~/content/controls/SearchCriteria.ascx");
sc.ID = "scDispCtl_" + idIt;
sc.ControlMode = SearchCriteriaMode.Display;
sc.CurrentCriteria = item;
sc.ItemUpdated += CriteriaUpdated;
sc.ItemRemoved += CriteriaRemoved;
pnlDisplayCrit.Controls.Add(sc);
idIt++;
}
When first rendering the page, everything is displayed fine, i get all my data. When i trigger an update event, the user control event is fired correctly, but all fields and controls of the user control are NULL. After a bit of research, i had to come to the conclusion that the event is fired before the controls are initialized...
Is there any way to prevent such behavior / to override the page lifecycle somehow? I cannot initialize the user controls in the page's Init-event, because i have to access the Session-Store (not initialized in Page_Init).
Any advice is welcome...
EDIT:
Since we hold all criteria informations in the storage backend (including the count of criteria) and that store uses the userid from the session, we cannot use Page_Init... just for clarification
EDIT #2:
I managed to get past some of the problems. Since i'm now using simple types, im able to bind all the data declaratively (using a repeater with a simple ItemTemplate). It is bound to the control, they are rendered in correct fashion. On Postback, all the data is rebound to the user control, data is available in the OnDataBinding and OnLoad events, everything looks fine.
But as soon it enters the real event (bound to the button control of the user control), all field values are lost somehow...
Does anybody know, how the page lifecycle continues to process the request after Databinding/Loading ? I'm going crazy about this issue...

Dynamic controls are can be a nightmare. The trick is to make sure you rebind everything on the postback.

I figured out a solution ;)
If i work with the OnCommand event on the buttons inside the usercontrol, i can pass a CommandArgument. Now im binding the collection identifier to the CommandArgument parameter of the button which enables me to handle all postbacks inside the usercontrol.
<asp:Button ID="scUpdate"
runat="server"
Text="Update"
OnCommand="HandleCommand"
CommandName="update"
CommandArgument='<%# CriteriaId %>' />
This declaration preserves the CriteriaId (a Guid) throughout postbacks and enables me to identify the modified entry on the underlying collection (managed on the page). The following code snippet shows how the event to the subscribing page is triggered.
scEArgs = new SearchCriteriaEventArgs
{
TargetCriteria = new Guid(e.CommandArgument.ToString()),
SearchComparision = ParseCurrentComparer(),
SearchField = scFieldSelection.SelectedValue,
SearchValue = scFilterValue.Text,
ClickTarget = SearchCriteriaClickTarget.Update
};
if (ItemUpdated != null)
ItemUpdated(this, scEArgs);
Maybe this answer helps somebody so i'll just post it ;)

Related

ASP dynamic usercontrols in a gridview do not update

I have a got Gridview, that gets its data by:
internal void updateGrid()
{
List<String> data = dt.getAlldata(UserID(), ListID());
gridViewer.DataSource = data;
gridViewer.DataBind();
}
After a button click the database is updated and the new data is shown. Everything works fine.
Now I have to replace the string with an Usercontrol:
internal void updateGrid()
{
List<String> data = dt.getAlldata(UserID(), ListID());
gridViewer.DataSource = data;
gridViewer.DataBind();
for (int i = 0; i < gridViewer..Rows.Count; i++)
{
UCControl dum = (UCControl)LoadControl("~/UCControl.ascx");
dum.SetData(gridViewer.Rows[i].Cells[0].Text, false);
gridViewer.Rows[i].Cells[0].Controls.Clear();
gridViewer.Rows[i].Cells[0].Controls.Add(dum);
}
}
After first Page_Load(), everything is shown correctly. But when I click my buttons, the Usercontrols do not repaint. The data is set correctly inside, but it does not update.
Because this Control reacts by javascript on UserInputs on the client side, every Usercontrol has got his own Id that is set by
this.ID = "UCControl" + data[0];
data[0] is unique, but known during the whole process.
Can somebody tell me why the UserControl does not repaint? Or better: How do I tell the Usercontrols to update?
From your code I would say that once the data is bound then you can't go in immediately after and start to change it. You would need to hook into one of the databinding events.
If you were using a list viem ItemDataBound would be a good candidate to hook into. But the GridView has a more limited set of events and doesn't offer that level of control - so you are a bit stuck on that score.
In my experience using dynamic controls in asp.net (LoadControl) is just a bit fraught. I think a better option would be to publicly expose a property in your user control and bind to that.
This question gives a good description of how to achieve this
asp.net user controls binds inside gridview
Hope that helps

How is this explained with ASP.NET page life cycle?

I have the following code, which simply inserts a record into the database, based on some text fields and a dropdown. The dropdown gets bound in the Page Load Event.
protected void btnAdd_Click(object sender, EventArgs e)
{
try
{
Personeel p = new Personeel();
p.achternaam = txtNaam.Text;
p.naam = txtVoornaam.Text;
p.fk_afdeling_id = Convert.ToInt16(cmbAfdeling.SelectedValue);
BLLpersoneel BLLp = new BLLpersoneel();
BLLp.insert(p);
lblFeedback.Text = "Done and done!";
rptPersoneel.DataBind();
}
catch (Exception err)
{
lblFeedback.Text = err.Message;
}
}
protected void Page_Load(object sender, EventArgs e)
{
if(Page.IsPostBack == false)
{
BLLafdeling BLLa = new BLLafdeling();
cmbAfdeling.DataSource = BLLa.selectAll();
cmbAfdeling.DataTextField = "naam";
cmbAfdeling.DataValueField = "afdeling_id";
cmbAfdeling.DataBind();
}
}
My question is about IsPostBack.
On first load, the page has no PostBack, so it will bind the data to the dropdown "cmbAfdeling".
Then, when submitting the form, there IS a postback, so we don't reach the code inside the if statement. To me, that would mean that ASP.NET would NOT bind the data to the combo box.
However, the data is still there after submitting (and thus having a postback).
How is this explained?
This is due to the ViewState. The data in the ComboBox is stored in the ViewState and is sent back & forth during postback.
This might be worth reading to understand what is happening: http://msdn.microsoft.com/en-us/library/ms972976.aspx
It's explained by a concept called viewstate:
If you examine the code produced by your asp, you will find some hidden fields, one of which is the "viewstate". The viewstate saves the important values of your asp in order to be able to populate the elements every time the pages gets loaded, even if it's after a postback.
The data is maintained during postback, as you don't clear the data during postback or on load it will persist.

Click event not detected in UserControl

I've some UserControls which are created dynamically, with parameters :
foreach (DataRow dr in drc)
{
question = (from ques in bdd.QUESTION where ques.ID_QUESTION == idQuestion select ques).FirstOrDefault();
List<Object> listParams = new List<Object>();
listParams.Add(question);
AdminQuestion qa = (AdminQuestion)(Controller.LoadControl(Page, "~/UserControls/AdminQuestion.ascx", listParams.ToArray()));
pnl_question_list.Controls.Add(qa);
}
This is a method I found on SoF and it works great.
This method is called when I click on a button, and all my usercontrols are correctly created.
In this usercontrol, I have a button :
<asp:Button ID="btn_validation_modify_question" runat="server" Text="Modifier"
CssClass="clear_left_float_left myBouton myBoutonEnvoyer"
OnClick="btn_validation_modify_question_Click"/>
And my method :
protected void btn_validation_modify_question_Click(object sender, EventArgs e)
{
QUESTION q = (from m in bdd.QUESTION where m.ID_QUESTION == question.ID_QUESTION select m).FirstOrDefault();
q.MESSAGE = txt_modify_question_message.InnerText;
q.ID_THEME = new Guid(ddl_modify_question_theme.SelectedValue);
bdd.ApplyCurrentValues<QUESTION>("QUESTION", q);
bdd.SaveChanges();
}
But when I click on the button, it don't apply the method, and reload the page, like if I didn't have any declared method.
Is there something I don't know? I already used this technique and everything worked...
If you add controls dynamically, you'll normally need to do it on Init or PreInit page events. Otherwise event handlers will never work.
So, dynamically added controls must be programmatically added to the Web page on each and every page visit. The best time to add these controls is during the initialization stage of the page life cycle, which occurs before the load view state stage. That is, we want to have the control hierarchy complete before the load view state stage arrives. For this reason, it is best to create an event handler for the Page class's Init event in your code-behind class, and add your dynamic controls there.
Note You may be able to get away with loading your controls in the
Page_Load
event handler and maintaining the view state properly. It all depends on whether or not you are setting any properties of the dynamically loaded controls programmatically and, if so, when you're doing it relative to the
Controls.Add(dynamicControl)
line. A thorough discussion of this is a bit beyond the scope of this article, but the reason it may work is because the
Controls
property's
Add()
method recursively loads the parent's view state into its children, even though the load view state stage has passed.
Here you have more information.
EDIT
Just to be sure we're talking about the same, here you have how your code should look like
protected void Page_Init(object sender, EventArgs e)
{
...
foreach (DataRow dr in drc)
{
question = (from ques in bdd.QUESTION where ques.ID_QUESTION == idQuestion select ques).FirstOrDefault();
List<Object> listParams = new List<Object>();
listParams.Add(question);
AdminQuestion qa = (AdminQuestion)(Controller.LoadControl(Page, "~/UserControls/AdminQuestion.ascx", listParams.ToArray()));
pnl_question_list.Controls.Add(qa);
}
...
}
PageLoad(){
If(!Page.IsPostBack())
foreach (DataRow dr in drc)
{
question = (from ques in bdd.QUESTION where ques.ID_QUESTION == idQuestion select ques).FirstOrDefault();
List<Object> listParams = new List<Object>();
listParams.Add(question);
AdminQuestion qa = (AdminQuestion)(Controller.LoadControl(Page, "~/UserControls/AdminQuestion.ascx", listParams.ToArray()));
pnl_question_list.Controls.Add(qa);
}
}
Did you try with this solution? And not use Page_Init()?

Maintaining GridView current page index after navigating away from Gridview page

I have a GridView on ASP.NET web form which I have bound to a data source and set it to have 10 records per page.
I also have a hyper link column on the GridView, such that a user can navigate to another page (details page) from the list. On the details page, they have "Back" button to return to the GridView page
Edit
Just to clarify the query
I am looking for sample code snippet on the Server Side on how to specify the page index to set the GridView after data binding. The idea is to ensure the user navigates to the same page index they were on.
The three basic options at your disposal: query string, session, cookie. They each have their drawbacks and pluses:
Using the query string will require you to format all links leading to the page with the gridview to have the proper information in the query string (which could end up being more than just a page number).
Using a session would work if you're sure that each browser instance will want to go to the same gridview, otherwise you'll have to tag your session variable with some id key that is uniquely identifiable to each gridview page in question. This could result in the session management of a lot of variables that may be completely undesirable as most of them will have to expire by timeout only.
Using a cookie would require something similar where cookie data is stored in a key/data matrix (optimized hash table might work for this). It would not be recommended to have a separate cookie name for each gridview page you're tracking, but rather have a cookie with a common name that holds the data for all gridview pages being tracked and inside that have the key/value structure.
Edit: A small code snippet on setting the page index.
protected void Page_Load(object sender, EventArgs e)
{
if(!IsPostBack)
{
try
{
if(HttpContext.Current.Request["myGVPageId"] != null])
{
myGridview.PageIndex = Convert.ToInt32(HttpContext.Current.Request["myGVPageId"]);
}
}
catch(Exception ex)
{
// log it
}
}
}
I'm more of a fan of the Session approach, personally. Simply save your page index as a session variable, and, if this Session variable isn't null on page load, use it to fire your "OnPageIndexChanging" method, like so:
Set your current page number whenever the page number changes:
protected void GridViewIndexChanging(object sender, GridViewPageEventArgs e)
{
myGridView.PageIndex = e.NewPageIndex;
Session["pageNumber"] = e.NewPageIndex;
//whatever your page index changing does...
}
Then, on Page_Load do something like:
if (!IsPostBack)
{
if (Session["pageNumber"] != null)
{
GridViewIndexChanged(myGridView, new GridViewPageEventArgs((int)Session["pageNumber"]));
}
}
you can ues the Page Index Change Event of Gridview and Find out the Current Page Index for e:g
yourGridId.PageIndex=e.NewPageIndex;
ViewState["GridPageIndex"]=e.NewPageIndex;
on PageLoad Get the Viewstate Value
string pIndex=string.Empty;
pIndex=Convert.toInt32(ViewState["GridPageIndex"]);
if(!string.Empty(pIndex))
{
yourGridId.PageIndex =pIndex;
}
you must use query string and is recommended, otherwise you can use session object but don't use that for this as you may have grid view opening in different pages so use query string .
gridView1.CurrentPageIndex = (Request["pageNo"] != null) ? Request["pageNo"] as int : 0;
gridView1.DataSource = myDataSet;
gridView1.DataBind();
you can update your link on GridView_DataBound event

ListView -Dynamic Controls and DataPager events

I have a listView control which is bound to an object datasource. In the ListView1_ItemDataBound event, I am generating some dynamic controls. I do this because depending on a particular column value, i might need to generate textbox, radio button, check box etc.
Some code here:
ListViewDataItem item = (ListViewDataItem)e.Item;
typez = Convert.ToInt32(DataBinder.Eval(item.DataItem,"Type").ToString());
if (typez == 1) //1 means generate radibutton
{
string[] options = DataBinder.Eval(item.DataItem, "QuestionDetail").ToString().Split(new string[] { delimiter }, StringSplitOptions.None);
questionID = Convert.ToInt32(DataBinder.Eval(item.DataItem, "Question_ID").ToString());
int optionCount = 1;
RadioButtonList rbl = new RadioButtonList();
//set ID for the radiobtnList to the questionid no.
rbl.ID = "mcq_" + questionID;
foreach (string s in options)
{
//adds the MCQ options to list item
ListItem li = new ListItem(Util.GetAlphabet(optionCount).ToUpper() + ". " + s, Util.GetAlphabet(optionCount).ToUpper(), true);
rbl.Items.Add(li);
optionCount++;
}
//PlaceHolder PlaceHolder1 = (PlaceHolder)e.Item.FindControl("PlaceHolder1");
PlaceHolder1.Controls.Add(rbl);
I have DataPager also. When I go to the next page I want to somehow capture the user response in the previous page. Otherwise, all the user response is lost. I tried using ListView1_PagePropertiesChanging event. But here I somehow do not seem to get the dynamic controls in the page.
I need to get the radio button selected value so that I can save it or put in some session variable so that when user comes back to this page he can see his previuos values.
Could someone please suggest some insight on what I am doing wrong.
Problem is that you have to create controls in OnInit, then ViewState persister can do it's job. If you do it after OnInit, in ItemDataBound, when Postback is triggered, controls doesn't exists and their's viewstate isn't deserialized.
To access values of radio buttons and get selected one, you have to look at Request.Form dictionary and find it.

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