I have a datalist and want to dynamically add buttons to it. I am using the OnItemCommand datalist event and setting the CommandName/ CommandArgument attributes of the button.
However I am having trouble with handling the button click - does not seem to fire.
It works when I declared a button on the aspx page, but not for buttons that are dynamically created.
I hope this makes sense, and any help would be great.
Thanks
You can only create dynamic controls on PreInit or Init if you want to handle associated events. Otherwise, on postback, they won't exist at the moment of event handling and because of that, your handler method won't be called.
Internet is full of resources about how to handle dynamic controls. Let me know if you need any reference.
Related
I have a ASP.Net(C#) page. When a user selects a value in dropdownlist, some new controls will be visible to him.
I am able to that now, but the page has to reload every time and state has to be maintained between postbacks.
Is there any way to do the same without reloading of the page in a easiest way possible without using ajax control toolkit?
Additional info: the data for the dropdownlist is coming from the database, and some places it has to be all server side so i can't use javascript .
You can try this idea: http://msdn.microsoft.com/en-us/library/ms178208(v=vs.100).aspx. I have not try it before but it seems logical.
you should go through updatepanel. Put all the controls inside a updatepanel which you want to show on selectedindexchanged event of the dropdownlist and write code behind on selectedindexchanged event of the dropdownlist accordingly. Hope this will help you...
I'm creating a simple custom pager for repeater (or anything else, it doesn't actually matter because all I want from it is current page number). Pager has 3 public properties: PageSize, MaxResults and PageIndex.
First is set in markup, second is set on the page in Page_Load or EventHandlers when various buttons are clicked and repeater is databinding again. Third is decided by user when clicking on page numbers.
Page numbers are dynamically created LinkButtons with OnCommand set to method that launches my pager's OnPageChanged event to inform webpage that it need to reload data.
The problem is that in order to create correct number of page linkbuttons I need to know MaxResults. I will know it not sooner than in Page_Load and most probably even later. But as far as I know if I want my linkbuttons to fire events they need to be created before Page_Load when I don't know MaxResults...
Now I'm creating linkbuttons in Page_PreRender and event's don't launch. What is the solution for this? It looks like GridView's built in pager is also done with LinkButtons and it also can't know count of data before databinding but the events are firing.
Problem: Content Page with Wizard Control with UpdatePanel and Placeholder. Above the UpdatePanel is a DropDownList. I need to display different input controls below the drop-down list when the user changes the selection in the drop-down list. When the user clicks 'Next' on the wizard control, I need to be able to get the data out of those dynamic controls as well.
I know all the dynamic controls have to be created in the OnInit method in order to get the data back from those controls during the postback. However, when the drop-down list's SelectedIndexChanged event is fired, the OnInit method is called... then the PageLoad... and finally the handler for the SelectedIndexChanged event is called. ViewState hasn't been restored until well after the OnInit & PageLoad methods have been called, so there is no way to know what the user chose in the list box at the time OnInit is called... which exactly when I'm required to create the dynamic controls.
So... how do you solve this problem? Do you just have to write the entire page, or most of it, using JavaScript?
Thanks in advance.
I tend to use an old school method for this type of requirement. I would write all of the controls that are needed in the update panel, with their Visible property set to false. Then, on post back read the drop down's state and set the approperate controls Visible property to true. This way there is no "dynamic" controls, and due to the fact that controls whose Visible property is false are not rendered, they are not downloaded until the user should see them.
you can also use an asp:hiddenfield and set the value to a case var you mentally create. then run a small jQuery script on top to look at
$(document).on("change", "#ddlSelector", setControls);
then just make a function, for instance:
function setControls(event) {
event.preventDefault();
var selector = hiddenfield.val();
}
then any item to show/hide can be done with getting the tag:
$("#elementName").css("display", "inline");
or display, none to hide.
I used this at work because at times you need to change without firing the postback, but still collect data when they engage the form.
I typically avoid jQuery for many events for strength of code and security, but DOM element manipulation can be much easier at times with jQuery.
I was going through an article on event bubbling in asp.net and came to know that although it is possible to subscribe to the click event of a user control's button from the containing page, "doing so would break some of the object oriented rules of encapsulation". A better idea is to publish an event in the user control to allow any interested parties to handle the event.
My question is that exactly how does a direct subscription to the button's click event from a containing page would break the object oriented rules of encapsulation?
Apologies if its a dumb question. :|
Thanks!
The Button is supposed to be encapsulated by the UserControl.
If the Page binds directly to events on the button, then the page is now dependent on the inner workings of the UserControl.
The Page should be consuming the UserControl, not the UserControl's button. If the author of the UserControl later wants to remove the button and use some fancy new method of firing its "Submit" event, your page could be broken because the button may no longer exist.
For that matter, if the owner of the UserControl decides in v1.1 to rename the button from btnSubmit to SubmissionButton, it could break your page, as well.
Better to consume the UserControl and let it be concerned with its own inner workings.
The idea is that the button of the control is an implementation detail of the UI of the control. If you republish the click event you could reimplement that button as an ImageButton, LinkButton, etc.
I think it's OK to attach an event handler at the page level to the button if the button is a permanent fixture of the UI. It saves a lot of event code, especially with a lot of buttons.
My understanding of the order of page events is this:
Page : Load
Control : DataBind (for a GridView or whatever)
Control : Load
Control : Clicked (for a Button)
Page: PreRender
Control : PreRender
(There are lots of others - but these are the ones I'm interested in)
The important thing to notice here is that the button's click event comes after the gridview's bind event. If the button causes a change to the data, the GridView displays the old data. I could rebind the control in the PreRender event, but that seems totally ugly.
This must be a very common pattern (a button that updates data). How do I put this together so that the GridView binds to the data after the Button click changes it?
The answer was in the Button Click event, after the data has been changed, call DataBind() on the page to cause the GridView (and anything else that needs it) to rebind. I didn't realise you could do that.
Thank you Ocdecio & Mufasa - I would mark your answers as helpful, but I got no rep yet.
ASP.NET does, by default, lots of binding and rebinding. Rebinding after a click event is normal.
The only reason the button click event comes after GridView bind is because you programmed your page to do that . I don't see any problem in binding the control in the PreRender event, in fact that is the only way to take action after a control event (such as Button onclick).