Let's say I have a bunch of controls that I want to "repeat" on the page. The user can click "Add" to add another set of controls.
I still want the input to be kept (that the user has put in) after the postback that will be triggered when the user clicks "Add".
What is the best way to do this? I would like to use a repeater but then you have to (as far as I know) store the information in ViewState and then re-populate all the controls with the old data.
I am using ASP Web Forms.
Se picture for example: https://i.stack.imgur.com/rpmnG.png
Related
I'm trying to create multiple controls by using retrieved data from query, but preventing them from dissapearing on postback, allowing me to get and mantain their values, the problem I have is that I cannot create them on Init because the number of controls, their IDs, and other properties are only known after user selects an item on menu.
Page loads a Menu with all its items and values (Data dependent), plus, a button is loaded too
User clicks a item on menu.
Selected value is used to perform a query by using a Dataset (This happens inside a function which is called from Menu_ItemClick event).
Retrieved data from query is used to determine how many controls must be created (2, 4, 6, etc.). Each control has its unique ID, which is given according to data.
Controls are created and placed into a Panel (named p).
Now controls are visible and available for editing (RadioButtons, TextAreas)
User clicks on button to save information from dynamic controls into a Database
Problems I'm facing
Controls dissapear on postback when clicking button, because they weren't created on Init.
Placing button on UpdatePanel to prevent whole page postback, makes dynamic controls not accesible when trying this:
For Each c In p.Controls
...
Next
The only control it gets is a single Literal control (Controls count is 1), as if other controls didn't exist.
Thank you in advance.
When you wrote "Controls dissapear on postback when clicking button, because they weren't created on Init", did you mean to say that "Controls dissapear on postback when clicking button, because they weren't re-created on Init"? If not, then that is likely a root cause of your problem - dynamically-created controls must always be recreated in response to a PostBack (cf. ASP.NET dynamically created controls and Postback). There may be other issues as well, as dynamic controls in Web Forms can provide a lot of challenges as your scenario gets more involved - here's one article that lays out many of them under various scenarios http://www.singingeels.com/Articles/Dynamically_Created_Controls_in_ASPNET.aspx (e.g., if the user can re-select from the DropDownList to generate a different set of dynamic controls). The canonical reference on all of this is http://msdn.microsoft.com/en-us/library/ms178472.aspx.
Now, on PostBack you'll need some way to ascertain which controls were dynamically created so they can be dynamically re-created. As such, you'll need to store somewhere whatever information allowed you to dynamically create the controls. Since ViewState isn't available in Page_Init and there can be other issues introduced when using sessions, my suggestion is to simply declare a HiddenField that contains that state information. In Page_Init, you'll then need to get the HiddenField's value from Request.Form (since the value of your HiddenField won't be loaded until after Page_Init from ViewState) and go from there to re-create your controls.
My final suggestion: try getting everything working with a regular Panel first and then try and introduce the UpdatePanel - no need to over-complicate the problem at first.
I am trying to add user controls once the page is loaded.In the page depending on the selection (dropdown or checkbox) the respective user control will be added.I know that if we need to add user controls I need to add them in the Page_InIt method.but I will know which user control to add only when the page is completely loaded and the user has made a selection.
The page has Update panel so there will be many Async postback's so I also need to look at how to persist the user-control once it is added to the page.
Any help will be grateful.
You can get user selection using the
Request.Form["YourControlID"].
Check this link to know about getting postback data from forms
Read Post Data submitted to ASP.Net Form
Also read this post about using dynamic controls in ASP.NET. It very helpfull.
TRULY UNDERSTANDING DYNAMIC CONTROLS
I have a Panel. Now in that panel, i'm adding controls. It is getting added and displayed.The problem is when the page is posted back.I know the controls have to be binded again in the panel. But lets say if the user has entered some value in the dynamic created text box. Its is getting lost..
I have done this before by storing the data from the controls in session.
Every time you dynamically add a control, store the current data entered into the controls in session or viewstate for example, and then rebind on postback. Not the most elegant solution but it worked. I take it this is a webforms question?
Add dynamic control click
Save current form data
On page_load load the data from viewstate into the controls
Make sure that the controls get the same ID each time (for ex. by specifying an ID explicitly)
and you should add the dynamic controls on Page.Init so they can participate in the page's life-cycle.
There's an article on 4guysfromrolla.com, Dynamic Web Controls, Postbacks, and View State
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.
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.