Hii,
I need to develop an online quiz website that would be having MCQs. I would want to have one question appearing per page with a Numeric Pager so that the user can go back and forth.
I tried using the FormView for displaying the questions and RadioButtons. I created a class QANS that would hold the answer selected by the user for the questions that he did answer so that I can later sum up the total Score.
Now, the problem I'm facing is as below:
Let the user select a RadioButton, say R, on a PageIndex, say I, and then go to some other page, say K. When the user returns back to page I, none of the RadioButtons is selected.
I tried adding code for setting the Checked property of the RadioButton true in the Page_Load(), but it didn't help. I also tried the same with the PageIndexChanged and PageIndexChanging event, but the RadioButton doesn't get checked.
The RadioButton that was selected for a particular question has been stored and I am able to print which one it was using Response.Write() but I'm not able to keep the RadioButton Checked.
How shall this be done?
You should be able to make the radio button checked in the
protected override void OnPreRender(EventArgs e)
event of the page lifecycle
Have you considered using the .Net wizard control for this?
The ASP.Net 2.0 Wizard Control
You can save the state of the selected controls in session and repopulate them after the round trip.
It's odd that it's losing state after the postback. Is there any crazy code in you on_load or pageIndexChanging or anything?
From what I understand, you have to persist the checked state of the radiobutton across the pageindexes. You can use ViewState for that as that can preserve data across postbacks for a page.
something like this:-
// Define a list of question ids attempted
List questionIdsAttempted;
//Add the List to the ViewState
if(ViewState["QuestionIdsAttempted"]!=null)
{
questionIdsAttempted= new List()
ViewState["QuestionIdsAttempted"] = questionIdsAttempted
}
// Add the question id to the list when when the user attempts a question
questionIdsAttempted.Add(qId);
// Add the list back to the viewstate
ViewState["QuestionIdsAttempted"] = questionIdsAttempted
And in the page load in checked attribute of the radiobuttons , you can call a function with the current question id and the function will get the list from the viewstate and returns true or false based on if the id exists in the list.
Ofcourse, you need to check the nullability of the viewstate in various places based on the flow of the program.
Let me know
Related
I have an ASP.NET web form on which I'm displaying a list of database items via user controls, generating the user controls dynamically - working fine.
Also on the page, I have an asp:dropdownlist filled with items that can be added to this database list. Along with this dropdown I have a button 'ADD'. My intent is that the user chooses and item, clicks add, and then the list of user controls on the form will include this new item.
I have all this working.
My issue is that the user control has a button 'DELETE', which removes the selected item from the list. That works, EXCEPT when I add a new item. Because my 'add' button event is always fired after Page_Load, even if I regenerate the list of user controls, the internal user control click events won't fire because the controls weren't created as part of Page_Load.
I need to know what I'm doing wrong, or best practices here, any advice. I tried to be precise in the description of the problem, but if I've not succeeded, let me know and I can add more details.
SIMPLE RESTATE: I need to know how to add a dynamically created user control to a page via a page button click event, and still have the user control internal click(etc) events firing.
Thanks for any help.
EDIT: Based on the feedback from the gentlemen here, and doing some further research related to their suggestions, I ended up implementing a solution based on what's presented on this page:
http://ryanfarley.com/blog/archive/2005/03/11/1886.aspx
Here's a snippet showing how I dealt with this. This snippet resides in my PreInit event handler. Not exactly an elegant weapon for a civilized age, but sometimes a blaster is all you've got to use.
'Look to see if button for adding a new client number has been
'clicked. If so, call the sub to add the item NOW, so that it
'is able to have it's internal click events fire.
For Each control_string As String In Request.Form
Dim ctl As Control = Page.FindControl(control_string)
If (ctl IsNot Nothing) AndAlso (ctl.ID = "cmdAddClientNumber") Then
Me.AddClientNumberToList()
Exit For
End If
Next
On the button handler, you initially add the UserControl to the Page. OnPreInit (which will next be fired when the user clicks Delete on the UserControl), you should re-add the UserControl - so that it exists, and can handle the Delete button event.
You will need to devise your own state tracking mechanism to determine that you need to add the UserControl during PreInit. I generally use ViewState, as evidenced by this seemingly similar post.
Similar question:
How to create and use custom control with UpdatePanel added to the page programmatically
Dynamic control should be re-added to the control tree OnPreInit, see documentation:
PreInit - Create or re-create dynamic controls.
ASP.NET Page Life Cycle Overview
This is a little difficult to explain so please bear with me.
I have a procedure that is generating some radio buttons and assigning a CheckedChanged postback event based on the level being passed through (up to 4 levels). When the first level is checked (radio button selected) the postback event rb_CheckChanged00() is called and a check is done to see if this item has any children, if it does, it will create more radio buttons and assign rb_CheckChanged01 to the CheckChanged event for these - This part is working fine.
The issue I have is when I select the second Radio Button that has been created (the child), it doesn't seem to go to the post back event at all. The page is posting back when I click on it but everything resets because it won't go into rb_CheckChanged01.
I know this info is quite vague but I am hoping someone has an idea on how the post back event works and if I am somehow using it incorrectly.
Using: ASP.NET 2.0, IIS7
Thanks.
Most of the time when the dynamically created control's events are not fired, it's because the controls are 'reset' upon postback.
To make sure the same controls get created each and every time make sure that the control's IDs are set to the same values each and every time, before the ViewState is loaded. This way, when the control is added to the control collection of the page, once the ViewState is loaded, it'll persist it's properties. (just to describe what happens, in a nutshell)
One of the best articles I've read on this topic is this one. Make sure you read it, to fully understand what's happening in the background.
Looks like the child RBs are cleaned before they are able to trigger the event. From my personal experience, it's best to keep track of those dynamically generated objects, and regenerate them in every postback. The events will start to trigger :)
Your controls and events are not registered in the ViewState because dynamic controls need to be loaded in the Page_Init. Because they're not persisted in the ViewState, they won't be registered with events. A similar question:
Problem with dynamic controls in .NET
Only 1 thing can cause this, you create the rb's on page_load and don't add them to a List<> or something similar and that object to Session. What you need to do is when you create the items, Add them to a List and add that list to Session["RadioButtons"] and if the Page.IsPostBack is true, load your controls one by one from your list which is kept in your session to your page.
Lets say I have three DropDownList controls in a web user control and they depend on each other.
Categories
Brands
Products
Explanation:
After I choose a category from Categories dropdown list, related brands are loaded in Brands DropDownList and same happens when I choose specific brand and they are all located in a web user control since I am using it too much on different pages, I don't want to copy and paste the same code on all the pages.
Problem: The pages can contain a GridView and DataSource control which needs an additional Where parameter to fetch all the data needed in and that parameter could depend on selected product within the Products DropDownList control.
Question: So how can I get that Selected Product Value from Products DropDownList to bind it to SQLDataSource or any other DataSource control.
My Thoughts: I belive I can solve this problem in the ways following.
I can use static variable which is updated once Products selected. That field variable could be public so everyone can reach it
Selected Products DropDownList can create a QueryString Field for me to grap the selected value.
In the same way, the dropdownlist can create a Session variable on the fly and I can fetch the value
It can create a hidden field maybe.
But: Well those are some of my thoughts but I found them so naive to implement. I need something elegant and satisfying to solve this problem. It should be something like a gateway from the Web User Control to outside world.
Maybe a separate class or a Property can help me in the gateway solution.
Anyways, I am waiting for your answers.
If I'm understanding the question correctly:
You can add a property to the user control that exposes the products DDL selected value.
You can also add and raise an event from the user control that fires when the products DDL selected value changes. Creating a custom event argument that contains the product value, allows it to get passed directly to the event handler.
Then your pages can handle the event raised by the user control, have the product value, and bind the grid.
You could bind the DropDownList.SelectedIndexChanged events to the same function, and test the SelectedValue properties of each DropDownList. If their SelectedValues are valid, bind the grid to your DataSource.
I've done this in the past when I needed users to input a certain amount of data before I could query the database. I set the Hidden property on my GridView if the DropDownLists weren't valid, and reset it when they were properly bound.
I'm trying to create a web page that will display an appropriate user control based on the selected value of a drop down list.
Basically the page layout is this:
Drop Down Selection
< User Control created based on drop down selection >
I have it half working... the controls are changing when the selection changes.
In OnInit(), I dynamically create the last selected control (whose value gets saved in session state because ViewState isn't available at OnInit).
When the drop down selection change occurs, I remove the old user control, and add a new one. The problem is: with the new control being added from the selection changed event, I'm not able to save changes from the user on the first postback. After the first post back, the selected control is created from OnInit instead of the Change event, and state is saved from then on, until the next selection change.
Here is the SelectionChanged method:
protected void SelectionChanged(object sender, EventArgs e)
{
SelectedValue = int.Parse(DropDownList.SelectedValue); //Store in Session
Control userControl = GetSpecificUserControl(SelectedValue);
PlaceHolder1.Controls.Clear(); // Remove old user control
PlaceHolder1.Controls.Add(userControl);
}
Any changes made to the new control by the user after SelectionChanged happens are not saved on the following post back. However, subsequent postbacks do get saved. At that point, the control is getting created in OnInit().
Is there some way to force the correct post back and ViewState when the control changes? Is it possible to force a page reinitialization after the control is changed?
What you need to do is keep the last known value of the DropDownList in the Session. Then:
OnInit:
Create whatever control is indicated by the saved value in the session
SelectionChanged Event
Remove whatever you created during OnInit
Create and add new control based on new DropDownList selection
Save new DropDownList selection in session
This way, on the next postback after a change you are re-creating the control that ViewState expected to find, and so it's state will be restored.
Dynamic controls can be very finicky. Often it is easier to create all of the controls you might possible need and set their Visible properties to false. This way they don't render to the browser at all. Then set Visible to true for just the controls you need when you need them.
This is the classic tear-your-hair-out problem with ASP.Net webforms. You have several options:
1) This is a bit of a hack, since it goes outside the intended page lifecycle a bit, but in my experience it's the most direct way of dealing with the problem. When the page posts back from the drop down selection event, simply poll Request["MyDropDownID"] for the selected value of the drop down control during Init() - don't wait for the OnMyDropDownChanged() event to set up your page.
2) Implement your own ViewState handling for your user controls. This requires digging into the ViewState documentation and overriding a number of methods.
3) Joel's solution. He beat me to it but I was trying to get first post :p
Other options involve posting values using javascript and such, but those get really messy.
If the list of options is not too big, you could just render all the user controls statically and use JavaScript/jQuery to show/hide the appropriate controls based on the value of the dropdown (onchange js event). You can use the dropdown value to extract the appropriate values from the user controls when saving.
You avoid the pain of dealing with dynamic controls, provide a more responsive UI when selecting from the dropdown (no postback), etc...
Don't add the control in the SelectedIndexChanged handler, add it during Page_Load. You'll just have to test the value of the dropdown each time the page loads, and load the correct control for that value.
Well i have a gridview where i have defined the columns on my own and turned autogenerating off but now i have the problem that i cant access GridView.SelectedRow.DataItem.
As it turns out to be null now, when it had a value when auto generation was turned on..
Edit:
What i need is a way to save the ID of the row while not showing the ID to the user so if there is any way to do this?
I'm guessing DataItem is only properly filled when you are using DataBinding.
Are you using DataBinding?
Ok from this url:
The GridView (and actually, all our
data controls) does not save data
items across postbacks. This reduces
ViewState (if the objects are even
serializable) and enables garbage
collection to happen and clean up your
objects. So, when you click the
button to post back, the GridView has
not called DataBind and therefore your
data item isn't there. This is what
you've discovered.
Guessing you're reading the value from a postback, might just be the problem.
Try using SelectedValue, if you've setup the (primary) key for the items.
I've always used that and it worked.
msdn about SelectedValue
You can create a new hidden template column that will have a label with the ID . and in the cs file you use .FindControl on the rows.
You also have DataKeys property on the gridview, witch I think also does what you want