I have written the user control InputDetails that has a few text boxes and a few radio boxes inside it.
I add it dynamically during Page_Load:
if(!Page.IsPostBack()){
InputDetails input = (InputDetails)Page.LoadControl("InputDetails.ascx");
PlaceHolder1.Controls.Add(input);
}
but when I refresh the page, the control is gone, so I'm asking, how do I save the user control in the viewstate that it has been added, so it automatically reloads it next time. Better yet, how do I read the values put in the text boxes of the user control when the page is posted back? I need to be able to add multiple InputDetails on a single page so saving it would be useful.
If you add a control to the page dynamically, you have to recreate it after each postback.
Try to remove the if (Page.IsPostBack()) line and check if it works :).
For each control you create, you should also set the same ID value each time it's created.
If there are no other issues, the ViewState should then be able to save state of the controls across postbacks.
In order to read the values, you can:
add some public properties to your user control in order to get access to the values you need
or
use TextBox txtBox = (TextBox)myCustomControlObject.FindControl("nestedTextBox") method to find (more information here: http://msdn.microsoft.com/en-us/library/486wc64h.aspx)
You can load user controls / server control dynamically using AJAX also and viewstate requires controls ID to store the viewstate properly.
would you pls go through this link for more info
Related
In my asp.net application, I need to be able to dynamically add user controls based on data in a database.
For example, on page1, I will bind three elements to a repeater:
some html content
a user control
more html content.
The repeater on the page is surrounded by an updatepanel
(updatemode=conditional, childrenastriggers=false)
The user control also has it's own updatepanet
(updatemode=conditional, childrenastriggers=true)
So, what I have is something like this:
outer update panel<br/>
repeater<br/>
item 1 = html<br/>
item 2 = user control<br/>
user control update panel<br/>
user control content<br/>
/user control update panel<br/>
item 3 = html<br/>
/repeater<br/>
/outer update panel<br/>
The problem is, I don't get any events fired by my user control. I'm pretty sure I need to create the control in the page_init, but I'm a little unsure of how to do this, since I may have to create any number of user controls of different types, and place them at different locations on the page. Has anyone ever run into this problem before, and how did you solve it?
Steps
Add add a placeholder control to updatepanel.
In CS file create a instance of your usercontrol.
Add that control to placeholder.
First off, I have managed to create a web application where my dynamically created user controls are recreated and repopulated with the correct information upon postback. I am not sure what my problem is, but i hope that you will be able to help me figure it out based on my situation:
On my page i enter the number of controls to be created into a hardcoded textbox (its on the aspx page) and click the okay butten. This in turn, creates the specified number of user controls dynamically using c# in the background.
So far the desired number of dynamic controls are in a table on the page.
Next...
I have 1 textbox and 4 dropboxes on each dynamic user control. When i type a company name into the textbox field and press enter or click away (on text changed event) it autoposts back and the textbox retains the company name that i have typed in.
Based on this string the dropboxes are populated from the database. Now when i select the desired items from the dropboxes and click on the save button (located outside of the dynamic controls, on the page) it does an insert to the database, but it turns out that upon this postback the indexes from the dropboxes have been reset and the wrong values get inserted.
The following pictures show firstly, how it should be and then how it is.
Basically the company name remains in the textbox of the dynamic control, but the information i choose from the dropbox resets to the first index.
It's hard to tell what happend without code, but this is a common mistake:
If you fill/create the dropdownlist controls in the page load event and you post back, the code will refill/recreate the controls. That's why you have to use something like If(!IsPostBack) in your page load event. Otherwise it will execute that code everytime you do a postback and actually just want to execute the code in your event handler for that button.
If you're dynamically creating the controls, make sure to do that in the Page_Init event. Dynamic controls have to be recreated on every postback. Their state is restored after the Page_Init (if it is a postback), so make sure to only set their values in Page_Load if you want to overwrite them.
I am developing a dynamic website in ASP.NET. As a trial I tried a code shown below, that adds some controls to Panel1. When user clicks a button for the first time the controls are added to the Panel but when user clicks the same button for second time, the previous controls are replaced with new ones. But I want the controls to be appended one after the other each time the user clicks the button. The code is something like this:
Control c=Page.LoadControl("DData.ascx");
Panel1.Controls.Add(c);
I also tried
Control c=Page.LoadControl("DData.ascx");
Panel1.Controls.AddAt(Panel1.Controls.Count,c);
But this replaces the first output. Please tell me how to append these controls?
As you would expect, this appends a single control:
Control c = Page.LoadControl("DData.ascx");
Panel1.Controls.Add(c);
You can append as many controls as you wish in this fashion.
However, you need to keep track of the controls you are adding in some persisted/stateful fashion (database, Session, ViewState, etc.).
You need to rebuild the control tree every time the page loads.
See my answers to similar questions:
https://stackoverflow.com/a/10050755/453277
https://stackoverflow.com/a/9545079/453277
It may be about the life cycle of asp.net page. Each time when page loads it returns to the initial state. Button Click events are handled after page load and you have only one control at the page. Please look Button to dynamically add controls everytime it's clicked
I'm adding controls at run-time to the Page Form object.
Each control has an Id.
On postback, I want to be able to access these controls and their values.
Currently, when I do a postback, the form has no controls in the Form.Controls Collection.
How can I rectify this?
Is this only possible if you add the controls to the page every time the page loads?
Dynamically added controls need to be added with every page load or else they will be lost.
However the viewstate of these controls can be maintained as long as they always get added with the same ID.
I believe you have to add the controls dynamically in order to access them on postback. So if you add a textbox dynamically, your event handler can't retrieve its value unless you add it again.
EDIT: One workaround I used was to add a predetermined set of server controls to the page and then use JavaScript to hide/show those elements. You avoid postbacks and you avoid the unnecessary tom-foolery associated with retrieving values from dynamically added server controls. Of course, this limits you to a predefined number of controls.
This was a big pet peeve of mine with ASP.NET web forms and is a factor in my decision to explore ASP.NET MVC - no more viewstate/postback mess.
using c# (asp.net)
i'm programmatically creating several drop down lists (random number).
the user selects a particular value from each list and i need to save the user selected value.
if i try to save the data to session state by using a button click event it says the drop down list object hasn't been created. (obviously cuz i'm creating the drop down lists in the page load event under !IsPostBack.)
if i try to save the data to session state in the page load event under IsPostBack i only get the first value from each list. (obviously cuz when the page is recreated after the postback, the drop down lists have been recreated and the user entered data is lost).
How do i save the user selected value from the drop down lists when a button is clicked?
i'm doing this in the code behind file.
As John Saunders said, you have to recreate all of your DropDownList controls on every postback. Additionally, you have to create them before state is restored. That means that "under !IsPostBack" in the page load event is already too late. Move it up to Page Init.
You have to recreate all of the dropdowns on every postback.
Personally (without the ability to switch to MVC) I would consider getting rid of the postbacks altogether and reading the values back directly from a standard HTTP POST request.
The implementation of dynamic controls with postbacks often ends up rather convoluted and difficult to follow