I'm working with an aspx page, where once I click on a button, some calls are executed in the background and I display the returned information on the webpage. I do this by adding this information to a panel:
panel.controls.add(label)
panel.controls.add(anotherpanel)
Problem is that once I click the button again, and I get some new objects from the background calls the UI elements (those labels and panels) still remain visible and my new information is just added after the previous one.
I would like to have all the previous information gone once I press the new button.
I've tried panel.controls.clear(), but it doesn't do anything.
Any ideas? Thanks.
Have you tried setting a breakpoint and check to see that it is not the background calls returning the previous information along with the new ones?
I asked because items that were added programmatically, by itself, shouldn't persist across postbacks.
You might want to declare label and anotherpanel in the actual markup, and set their visibility to false. Then, just set the visibility to true and replace their values in your codebehind as you acquire results.
Related
EDIT: I needed to skip control creation during post back -- see my answer below.
I'm working on a very basic front end to a simple tool and I wanted to present some data in a much more sorted and useful way, instead of making one huge wall of text. I found this tutorial on building a simple tabbed interface using MultiView, but have run into a bizarre problem. I can't use Ajax tabs because of legal hissy fits over 3rd party software.
My webpage is a basic ASP.NET page with a user control plopped in the middle of it. In this control's ascx file, I defined the Menu (empty) and the MultiView (also empty) so that I can dynamically populate the tabs with content driven from an external file.
When the default page's OnInitComplete function is called, I call through to the user control to load the data file, then build out the tabs and the view content based on the loaded data. I tried doing this from PageLoad, PreInit, and CreateChildControls, but I kept getting an errors saying that I was setting the the MultiView's active view index at an invalid time (and also that there were 0 views despite the fact I just added a bunch of them):
ActiveViewIndex is being set to '0'. It must be smaller than the
current number of View controls '0'. For dynamically added views, make
sure they are added before or in Page_PreInit event.
But OnInitComplete appears to work just fine, so I went with that.
I iterate over the loaded data (multiple lists of strings), and for each list, I add a MenuItem with the list's title to the Menu and a View to the MultiView. The View is populated with a table->row->cell as in the above tutorial. In the cell, I add the list title and a CheckBoxList data bound to the list of strings.
So far so good, but when I click on a tab (or one of the checkboxes, etc) and there is a postback or something like that (the screen flashes as the site redraws itself), there is now a duplicate set of MenuItems immediately after the original. Each time I click on a tab or checkbox, another set of menu items are added.
I clear the MenuItem's Items list prior to building the controls and I verify that the controls hierarchy is structurally as expected after the control construction. Yet when one of my callbacks is called, my MenuItem list magically has some items added to it. None of my other controls appear affected at all. As a hack, I can remove the duplicates manually in my menu's OnMenuItemClick event, but I'd have to do the same in any of the callbacks I receive. Obviously I'd rather prevent this from happening. This has me stumped and I haven't been able to find anything online about it. Why would one set of controls have some content duplicated, yet every other control maintain its state correctly? My code is really simple so there isn't a way to add additional menu items without also adding the views. Anyway, there are a correct number of items prior to clicking on the tab/checkbox, an additional set immediately following in the callback.
This is my first time using ASP.NET, so I'm learning as I go. :) Thanks!
My problem was that I was not testing for postback before creating the controls. The code below is working for me.
In my user control's code behind:
protected void OnInitComplete( EventArgs e )
{
if( !Page.IsPostBack )
{
CreateMyControls();
}
}
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've come across the strangest bug pertaining to DataGridViews in Windows Forms.
I have a TabControl, that is supposed to contain a docked DataGridView in each tab page. I thought it would be convenient that the grid is focused upon changing the tab page, so that the user could simply hover the mouse over the grid and start scrolling when he changes the page. So, I just put a grids[tabs.SelectedIndex].Focus() in the event handler for changing the tab page.
However, something really strange happened. In my test application, I have three tab pages. If I try scrolling the grid right after starting the application, it doesn't work; I have to click in the grid first. I was expecting this. However, if I change the tab page, I can't scroll in any of the other grids until I click, except for the first one!
So, if I switch pages to the second page, then back to the first, I can automatically scroll that grid without clicking, but if I then switch to the third, I have to click for the grid to focus.
I had a look at the CanFocus properties of the grids, and it seems that only the first grid has it set to True. They are all created programmatically, and all in the same way. I don't see why they would be different.
Any ideas?
Inactive tab pages have their Visible property set to false. The documentation for CanFocus says:
In order for a control to receive
input focus, the control must have a
handle assigned to it, and the Visible
and Enabled properties must both be
set to true for both the control and
all its parent controls
Well, I solved it. Stupid programming error on my part, I had grids[tabs.TabIndex].Focus() instead of grids[tabs.SelectedIndex].Focus().
Oh well.
I have a main page into which i load a user control with a grid and add/edit link buttons.
If I bind the grid by setting the datasource and calling the databind() method in the page load event then it sets properly. However, I want to keep the selected row between postbacks, so I wrap the bind code in "if (!Page.IsPostBack) {}" as usual. My problem is the page load always registers it as a postback and my code never runs.
I am using the 2.0 framework, and my grid is an 2008.1 Infragistics for the 2.0 framework.
I thinking this must be something simple.... or hoping anyway!
Thanks in advance
If you place your control into an UpdatePanel, then you should check for Page.IsCallback instead of Page.IsPostBack.
The two ways I found round this were:
to load the user controls when the page is first loaded and then hide them until user selected what they need to see.
to load a new page into an iframe on the main page allowing it to have its own page control meaning when its loaded in at first its not a postback.
Not the greatest, but gets by.
Thanks for the help.
I have mixed feelings about necroing a thread this old, but the question is still relevant, and there weren't any great solutions offered, so though I would add what I recently did to solve the same issue:
I had a similar problem with a site I was building. My solution was to add a method to the user control called "OnFirstLoad" that does all of the stuff I would have wrapped in an "if not Page.IsPostback" block. I then call the "OnFirstLoad" method from the hosting page the first time the control is loaded into the control tree. This way the control itself doesn't have to worry about whether or not this is a postback, and the main page can initialize it as needed.