I have webform where a set of controls are generated in a Panel control during a SelectedIndexChanged event of a dropdown. That all works fine.
However, when I enter values in those controls and I click on my submit button, the controls are wiped out along with the data I entered.
I can only create the controls in that SelectedIndexChanged event because that's where I get the info to generate the dynamic controls.
What I'd like to do is keep those controls displayed with the data I entered and use the data I entered to do something else (like it happens in WinForms.)
Is this doable?
Thanks!
Every time a postback occurs you are working with a new instance of your page class. Dynamic controls added to the page during a previous postback went to the garbage collector as soon as the page for that postback rendered to the browser. You need to re-create your dynamic controls on every postback.
Save the count of "control-sets" in Session or ViewState, so that you can regenerate them with their appropriate ID's(f.e. appendeded with an indexOfControl) during Page_Init.
Here are some additional informations on:
View State and Dynamically Added Controls *
ASP.NET Page Life Cycle Overview
Extract:
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.
This is one of those areas where the attempt to make Webforms look like Winforms fails.
With Webforms, you need to do the whole dance of when to create controls. I believe all your controls will need to be recreated by some time around the end of PageLoad. There might be an event or two after page load that you can use, but generally speaking PageLoad is a safe time to create controls.
Essentially the controls need to be created before ASP.NET populates them with data from ViewState/Browser.
Related
I have two Repeater controls, each hosted in a user control. Both user controls are contained in the same aspx page. Only one User Control is visible at any one time. The repeaters are comprised of checkboxes, and text boxes for user input.
The aspx page is configured with an Ajax ScriptManager; and contains several Ajax UpdatePanels. These UpdatePanels result in partial page post backs when text is changed in a textbox control in controls on the aspx page (this is not the behaviour for the Repeaters in the User Controls). Through use of several AsyncPostBackTriggers, various controls contained in the other UpdatePanels on the page have their content refreshed in response to the partial page post backs they are configured be notified about.
Depending on a radio button group selection, I set the visible property to true or false – as appropriate for the User control containing a repeater control. The Repeater control is then populated with data using databinding. All of this works.
However, when the Submit button is clicked, the Repeater control contains no data.
Given that I am not dynamically adding the Controls containing the Repeater controls (but using Visible true / false). I would have thought that the State of the fields and the data in the visible control would be preserved during the post back.
The User Controls are contained within the UpdatePanel that contains the Submit Button.
I have explicitly Enabled View state without any effect.
Am I correct in assuming that I should not have to do any explicit handling of data changes the user makes (via client side script and manipulation of an Data Structure Representing the Repeater Data); and the View State should maintain the data I need to access on the server when submitted?
I do not believe that it is the User Control visible state changes that are causing the issue because when the page is initially loaded on of the User controls is populated with dummy rows (so it displays).
I am suspicious that because the visible state of the controls is changed during partial page post back, that the Page View State ends up with no knowledge of the User Control and therefore cannot track its data (or changes).
I have investigated a lot of similar sounding posts but so far do not feel that I have come across a solid explanation that can help me understand and fix the issue.
Hopefully someone can help.
I must be the only person who was unaware of the finer points of DataBind() method; be it called on a specific control being bound to data; or on the page itself. I hope the below helps others who find themselves in a position where data binding appears to be inexplicably lost'.
My problem was that my page was pretty complex. It has several User Controls on it. The problem was that in these User Controls, I was calling Page.DataBind() in the Page_Load event handler to 're-bind' the page data on PostBacks. This resulted in the Repeater control located on another User Control, to lose its data binding.
Removing the Page.DataBind method call from each of the User Controls on the Page_Load event handler method resolved the problem. It had nothing to do with Update panels / refreshes etc.
I have a simple user control containing two text boxes which I am adding to placeholder on Button Click event. I am storing the number(count) of clicks in View state and running a loop using count to create all previously added user control. I am also adding IDs to each User control (appending "UC" and count). I have also checked in view source the ids are same each time they are created. I have another button which basically does an post back. I have EnableViewState enabled ="true" in all controlls all the way up to Page Level.
My problem is that User Input does not persist on postback. please advice. Should this not be happening automatically for me?
Have a look at this:
http://www.denisbauer.com/ASPNETControls/DynamicControlsPlaceholder.aspx
I've encountered minor problems with it on a web farm, but for simple deployments its use is pretty straightforward. (Comes with source code, and the web farm glitch is a pretty simple fix.)
You need to create your dynamic controls in the Page_PreInit event rather than Page_Load or in a Click event handler. That way, they'll be there before ViewState, and then your posted values are applied.
I thinks what is happening is that you are creating your controls during the click event handler which happens AFTER ViewState and PostBack have been applied. This means your controls will be created empty each time.
I've put together a simple form to highlight the concepts of dynamic forms. What I need to do is add a control to the page when the user clicks the "Add" button.
I have a simple counter at the moment that stores the amount of controls created, which is incremented when the button is clicked.
At first I thought it would be as simple as calling RecreateChildControls (the class inherits from CompositeControl) on the event handler. This does create the new controls based on the incremented value, but all the control state is lost. I'm assuming this is because the event has been fired after the Init & Load phase.
Is there any other way to do this? I can get it to work by inspecting the postback value on the Init event, however this seems to be a little hacky.
This does create the new controls based on the incremented value, but all the control state is lost.
You're calling the function too late in the page life cycle. State is applied to your controls for the "Load" stage, and so if the controls are not created before that stage the state won't be restored, because the controls don't exist when it tries to apply the state.
You need to create the controls in the Page's Init event.
Personally, I'm not a fan of dynamic controls in ASP.Net. They have their place, but more often I choose a suitable maximum number of allowed controls, put them all on the page initially, and only enable/disable/hide/show them as needed.
I have a page, where I want to dynamically add asp.net user controls.
The scenario is that we want that on specific event of a control, It disposes itself and loads another control in the page.
I am not able to have solution about how to do this?
Anyone have decent idea?
Let's assume this scenario:
You have a shopping cart page.
The shipment control is loaded.
The user clicks on the next button.
--- Postback ---
The shopping cart page is loaded
The shipment control is loaded.
The event 'click' is handled by the shipment control.
The shipment control is disposed.
The payment control is loaded.
You can store a variable in the Session instance to determine which control needs to be loaded.
In the PageInit of the shopping cart page you retrieve the Session variable and load the corresponding control (step 1 & 2).
Make sure you do this in the PageInit in order for ASP.NET to fire the events.
In the event handler in the shipment control, you then update the Session variable (step 3).
In the Page_LoadComplete of the shopping cart page you dispose the shipment control (step 4) and load the payment control (step 5).
Scott Mitchell has written a great article about this scenario: http://scottonwriting.net/sowBlog/posts/3962.aspx
Webforms or ASP.NET MVC? I'll assume webforms...
Try using a CompositeControl. If there is databinding involved you can use the DataBoundCompositeControl. In the CreateCHildren method you dynamically create your controls add add them to the child collection. Here is an example of a fairly complicated DataBoundCompositeControl I created once (with event handling on inner child controls):
Scaffolding Control
This is actually a really hard thing to get right. Just remember to rebuild all of your child controls everytime and to store the state of the control so you can recreate everything properly.
You will rebuild everything twice on postbacks (and once on the first GET). Once to recreate the controls to their previous state and the second time to process the changes after databinding and event handling.
I have a site that I am currently working on in ASP.NET 2.0 using the usual WebForm stuff and ASP.NET AJAX 1.0. Is it possible to bind an event to a dynamically created control after the Page.Load event?
I have a table <td> element that I am dynamically creating similarly to this code:
' Create Link Button
lnk.ID = String.Format("lnkDetails_{0}", dr("Id"))
lnk.Text = dr("Name").ToString()
lnk.CommandArgument = dr("Id").ToString()
AddHandler lnk.Click, AddressOf DetailsLink_Click
cName.Controls.Add(lnk)
This this code is looped over for each row in a database (and of course more cells are added to the table, including an ImageButton with an event. The events work flawlessly when I execute this code during events leading up to and including Page.Load. I need to be able to fill this table with current data, which is updated during a btnClick Event elsewhere on the page, which occurs after this Page_Load event, so I am populating with old data. If I change this code to Page.LoadComplete, events stop working.
This data is a summary display of various components of an application, things like somebody's name, which when updated on a 'detail' form, updates the database by partial postback (a requirement), then it needs to show the update in this 'summary' section after an update. Currently it takes 2 postbacks to actually see the change in the 'summary' section, so effectively the summary is 1 step behind the changes (clear as mud?)
What would be the best way for me to populate this table with current data (which is available during/after Page.LoadComplete), but still have an event fire when a link is clicked (the event causes an UpdatePanel to display the 'detail' form).
I also have jQuery at my disposal and the usual ASP.NET AJAX methods, also javascript is a requirement for the website, so I do not need to degrade for unsupported browsers.
This is my first ASP.NET web application and need some help figuring out the best way to make this happen (I'm well versed in PHP, Django and the usual ways to do web forms - things like having multiple forms on one page o_O).
Update:
There really isn't a good way to bind control events to controls after Page_Load. The overall architecture of the pages is there is one ASP.NET form encompassing the entire page, there is only 1 aspx page. I am using master pages (however it doesn't have any obvious implications to my issue).
The page is split into a left and right 'pane', the left is a summary of all the data (in an update panel), the right 'pane' has 6 'tabs' implemented each as their own user control, each with several form fields and an update button all in it's own UpdatePanel.
An update on any of these tabs only refreshes the summary panel (UpdatePanel.update()) and its own panel. The 'refreshing' and event binding of dynamic controls of the summary from the db happens during Page_Load and the Update Button event updates db data. (The control event happens after Page_Load). I want to avoid doing a double post to get the summary to update, any thoughts are helpful.
You need to postback the whole page after your data changes in the 'btnClick Event elsewhere on the page'. It sounds like you have an UpdatePanel and it sounds like this is catching the postback of your btnClick event handler. Put the btnClick outside the UpdatePanel or change its triggers so that your btnClick forces a postback/refresh of your data. Or, redesign your table so it's AJAXly-refreshed when you click on btnClick, it's hard to get you more details without knowing more about the structure of your page and controls.
Good luck!
You can bind to an event whenever you want. It's just a simple event after all. But not all places might be suitable because you have to take into account when the event fires. And in most cases this happens between Page_Load and Page_PreRender. That includes the click event on a LinkButton. In general, I would recommend to add your dynamically created controls in the Page_Init stage.
You have to add the controls before Page.Load in order to maintain ViewState between postbacks, so use the OnInit event handler for that.
But once they're added, you should be able to bind event handlers (such as OnClick) at any point during or after the Page.Load... for example in your grid's ItemDataBound (or something like) or in the Page.PreRender.