I have an ASP.NET page where I am dynamically building LinkButton and TextBox elements. These elements are being built during the OnInit event of the page. The user can then perform an action that changes the values of these elements. The values of these elements are changed via JavaScript. When the user clicks a button, a server-side event is fired. This event parses the value in each control. I have noticed that the value for the TextBox is correct, but the value for the LinkButton is not.
Can only certain types of controls in ASP.NET be dynamically generated and have their values retrieved on the server side?
Thank you.
You can't get value of link button at server side. You can only get form elements' values at server side.
If you want to pass more values to server side, you can use hidden input elements.
No, generally you can create whatever element you like, given you create it inside the OnInit event or if you add the INamingContainer (marker) interface, you should override the CreateChildControls() method and create your elements in there.
But what do you mean by changing the value of the LinkButton via JavaScript? What exactly do you change on the LinkButton?? Could you provide more details?
Ensure that the "runat=server" property is set for each form element you want to retrieve via server code, and that you have an ID associated with each.
The textbox is working because value of the textbox is actually sent in the postback. But the linkbutton doesn't send anything back to the server. If you need to send something back that gets changed on the client, you'd need to set a hidden field and then modify your linkbutton using that value.
Related
I have a custom server control (composite control having dynamically created dropdown boxes and textboxes). I have enabled AJAX in order to avoid page reload.The server control is used inside the ASP.NET webcontrol having few buttons which controls the visibility of the server control. Now I enter values in the dropdown box and texboxes and click on any other button. After this postback the last entered values are gone! The control is not remembering the values. Can anyone help me? How can I retain the values after post back?
Ensure that the controls are given the exact same ID after each postback. Also you might want to try initialising your dynamic controls (DropDownList and TextBox) during Page_Init if possible.
If your custom server control is create dynamically all the controls, then you need to recreate them on every post, and you need to create them before the Page_Load(), or else the asp.net cant know them to filled with the post data.
To solve this, if you can not create them before the Page_Load(), then you can fill them by your self with the posted data by using the Request.Form[YourCustomControl.UniqueID] for all controls.
You need to re-create on each postback, see This article
From local forum i understood that PreInit can be used to handle the following
PreInit()
>Master pages can be called dynamically
>Themes can be set dynamically
>Programatically add controls to controls collection
and i read Init() is for
Init()
In this event, we can read the controls properties (set at design time). We cannot read control values changed by the user because that changed value will get loaded after LoadPostData() event fires.
Question
I am not getting the point "We cannot read control values changed by the user".Where do
users change the value of control?.Example would help me to understand the point.
PreInit: Raised after the start stage is complete and before the initialization stage begins.
Use this event for the following:
Check the IsPostBack property to determine whether this is the first time the page is being processed. The IsCallback and IsCrossPagePostBack properties have also been set at this time.
Create or re-create dynamic controls.
Set a master page dynamically.
Set the Theme property dynamically.
Read or set profile property values.
Init: Raised after all controls have been initialized and any skin settings have been applied. The Init event of individual controls occurs before the Init event of the page.
Lets say you have a textbox, a dropdownlist, some check boxes... the user enters data into them and you want to read their values by writing
var text = myTextBox.Text;
var selectedItem = ddl.SelectedItem;
this you cannot do before after the LoadPostData method has been called.
This page gives a pretty good summary of the different events and what they should be used for http://msdn.microsoft.com/en-us/library/ms178472.aspx. It says that PreInit should be used for ie. creating dynamic controls and Init for setting properties on them.
On the first post, you show several controls, say a textbox and a submit button.
The user types code into the textbox and click submit.
The user has changed the value of the control when he typed it in the textbox and it then got posted back to the page.
You will not be able to access the value typed in until LoadPostData has processed.
This is the pretty much the same with all other server side controls.
PreInit:
Initialize master page , user controls , dynamic controls
Init :
set the properties of controls
The value is changed through PostBack. The changes in the form data is determined by the current ViewState (which isn't loaded until later) vs the form data. Seeing as that isn't loaded until later, then you can't read any control values at that point.
I'm creating a custom ASP.Net GridView and I want to be able to alter the __EVENTARGUMENT value but I can't figure out how to capture the returned value on the server side.
I'm creating the ability to have a collapsible representation, so the first level is the standard GridView and I will insert additional rows via JavaScript if they expand the first level row.
My problem is how to create a link on the selecond level rows that posts back with custom data.
I believe the RaisePostBackEvent is where this value gets passed into; the base GridView class allows you to override it, so you should be able to tap into it there.
This is a part of the IPostBackEventHandler interface.
HTH.
Use __dopostback to raise the postback from javascript. Use the correct parameters so that this will be mapped to the right event
So i have an ASP.NET GridView control in which each column is a 'BoundField'. I did not create a TemplateField(ItemTemplate/EditItemTemplate), because i was planning on using JQuery to convert the BoundField row to a 'Edit' field by just converting the text in each cell to a textbox or textarea when that row was clicked. This is done all client side.
So far all the client side stuff works great. But I have a 'Save' button on each row of the grid that triggers an eventhandler on the server side. In that server side method, i try to grab values of that current row, but they are all the OLD cell values before I modified the fields/data using jquery/javascript.
When i iterate through each cell of the row, it's the same state as it was when it was rendered.
So what i'm trying to understand is. Why do all of this fancy javascript/jquery stuff when the state of the Grid stays exactly as it was when it was rendered when posting back to the server ?
someone please shed some light on this!!!
Thanks!
The GridView controls uses ViewState to persist its state between postbacks. When you do a postback it loads its previous state from the ViewState. Changes that you do via client-side Javascript are ignored. This is simply how the control works.
If you want to keep using the GridView control with inline editing, the easiest option would be to move to edit mode via a postback.
Another option is to have the fields in each row to begin with, only hidden. Then, you could show them via Javascript. You'll be able to access the values on the server.
Yet another option is not use a postback but an Ajax call, so that the grid is not re-rendered when you click the button. But that means you would have to manually collect the values from the grid via client-side code and pass it to the server.
I have a GridView that lists a bunch of items and one of the columns has a link that displays a modal (AjaxToolkit ModalPopupExtender). Let's call that link "Show". In that modal, I have a asp:button for saving the data entered in that modal. Let's call that button "Save"
So when the user clicks on a "Show" link in a certain row, I'd like write some javascript that sets something in the "Save" button, so that in my code-behind, I can handle "Save".Command and use the CommandEventArgs parameter to get the value.
Is this possible, or do I just need to use a hidden input tag and set its value?
Not a direct answer to your question, but another possible way of solving the problem:
Place a HiddenField control on the page. In your code-behind, before displaying the modal popup, set the value of that control to the ID of the row that was clicked (or the row number, or some identifying value). Then in the code-behind of your Save button, you can just read the value of the HiddenField.
Well, after continuing the research, it looks like it cannot be done. The CommandArgument property might reside in the ViewState, but for this case, it is completely server side and cannot be changed using javascript.
If you are using Updatepanel, you need to place the Hiddenfield inside the Updatepanel. Otherwise you will not be able to get/set the value stored in hiddenfield.