I am adding event handlers to a button like this:
btn.Click += new EventHandler(btn_Click);
However the btn_Click function is not being called (never hits the breakpoint in it) and the button just reloads the page. In my past experience, asp buttons usually perform the click code before reloading the page, so how do I get that to happen when the event is dynamically added?
I also set CausesValidation = false, although there's no validation on the page so I don't think that would have influence anyway.
The event handler needs to be bound for every request regardless of whether or not the page is being posted back. The binding of the event handler is lost at the start of each page request. Event handlers for buttons are typically bound in Page_Load.
You have to set event handlers on Load event (or before). If you do it after Load, it won't be executed since by the time the handler for the event is evaluated it won't be there.
Check this msdn article in relation to page life cycle. I think it will help you to understand. See that event handling occurs inmediatly after Load
Related
Let's say we have a pretty standard form with a textbox and a button (for simplicity). You want to handle a Click event and do some stuff based on user's input.
I was wondering, does it matter, when exactly you wire up an event handler for the Click event in a code-behind? If it does, where is the best place to put it? Page load? Page init? I've tried both places, but didn't notice any difference. Or it's just a personal preference of the programmer? I've already searched the internet couple of times, but haven't found any satisfactory answer.
I know when the actual method execute, just not sure about the wiring-up part.
As you know, there are several Page_xxx event handlers, like Init, Load, Prerender... This events exist in Controls, and Pages as well as User controls (in fact they're derived form Control, which holds all these events).
This events are related to the ASP.NET Page Life Cycle
If you read the page pointed to by this link carefully you will understand when the events are triggered. So, if you bind your event handler in any page lifecycle event that happens before the events are triggered, it's guaranteed that your event handlers will be bound in time to be triggered.
These are the main lifecycle steps:
PreInit -> Init -> InitComplete -> PreLoad -> Load -> [Control events] ->
LoadComplete -> PreRender -> SaveStateComplete -> Render -> Unload
Not all of them have associated events, but, if it's necessary you can override the corresponding OnXxx() function, like OnPreInit(). (This is usually only done on custom server controls).
You can bind events in Page_Init or Page_Load, because the control events are triggerd after the loading of all the controls has finished. The Load step happens in top-bottom way, first in the Page, and then recursively in all the children controls.
After Load finishes, the first events which are triggered are the Change Events, like TextChanged or SelectionChanged. Then are triggered all the other events, like Click.
If you bound the events in PreRender or Unload, they wouldn't be triggered. If you did in Init or Load, they would.
So it could look like it's safe to bind in Init or Load, but that's not true:
It could look like there's no special reason to bind them on Init or Load, because they'll be triggered later in the page life cycle. But, as the binding defined in the .aspx happens during Init, a programmer will expect that all events are already bound in the Load event. What would happen if this programmer raised an event of a child control in code behind? The Load event happens first in the root of the control tree, and them on all of the children, recursively. So, by the time the programmer is trying to raise the event of the child control, it won't be already bound. So this won't work as expected. This is more than enough to consider unsafe to bind events in Load event. That's why you should always bind events in Init.
Look at this diagram to see the order of execution of Page & children events:
ASP.NET Page Life Cycle Diagram
I have been wiring mine up in the control tag. If I do it this way it is clear that an event handler is present.
<asp:Button ID="btnRefresh" runat="server" Text="Refresh" OnClick="btnRefresh_Click" />
If I had to wire up an event handler in the codebehind, I would put it in Page_Load as a private function call.
I need to add onclick event to some dynamically added button, but when i click the button, the onclick event is not fired. I saw some solutions to this, like link which says I should create the controls and attach the event on page_init or page_load every time there is a request, but, will this make the website very slow if I have a lot of controls to add?
Yes, you must recreate dynamic controls if you want to access them and have their events fire on postback.
If you have so many controls on a page that your site is slow, you have a design issue. Rethink your design so you do not have so many controls on one page (perhaps several pages/tabs?).
Allocate memory like below to button in Init Page Event
Button b = new Button();
b.Click += new EventHandler(b_Click);
void b_Click(object sender, EventArgs e)
{
}
As told by #Oded, this approach can create Design issue.
When you have a Div like control IN YOUR PAGE which is supposed to consume this Button, then you can GIVE CSS styles to give it proper alignment and proper placement.
You have two option.
Add control at Runtime
Add control at Design Time
Definitely, site will go slow in case of many controls in both cases. As both options will take memory BUT, By End of the Page Life Cycle, all the controls will get disposed.
I have an ASP.NET user control with a button, and I want to add it to the page when the user clicks a button from another user control. I have created an event handler to the first user control to handle it from the page and add the second user control to a page. Everything is working normally, but the button on the second user control doesn't respond to the event.
I place the second control on RadAjaxPanel
Note: When I add the second user control at design time its working fine.
All dynamically created controls should be added by the end of Page_Init (though sometimes you can get away with them added by the end of Page_Load).
If you're only adding them based on a button click event then you've done this in the event handers which fire AFTER Page_Init and Page_Load in the lifecycle - This is why your events don't fire and why it works fine when you add at design time.
This is because when a button is clicked on the second user control - the whole page lifecycle starts again. The page goes through Page_Load and Page_Init first and your control doesn't get loaded here. So, when the page lifecycle handles the "handle postback events" part, the control no longer actually exists, so the event doesn't fire.
Conversely, when you add at design time, the control exists in Page_Init and Page_Load so is able to handle the postback events from the user control because it already exists in the control tree - if this makes sense.
You need to think how you can restructure so they're added by the time Page_Load has finished at the very latest or it won't work. Without code samples or more detail it's hard to suggest exactly how you might do this. One possibility would be to set it visible instead of loading it outright - but if the control does some 'heavy lifting' on load like database hits or API calls then this might not be suitable for you.
I did something similar. What I did was to load some controls dynamically based on a selection from a DropDownList. If you have a method which loads the control for you, let's call it LoadControls(), then you can do something like this:
DropDownList_Click {
ViewState("LoadControls") = true;
LoadControls()
}
By setting the ViewState variable, you can then indicate Page_Load to load the controls on future postbacks:
Page_Load {
if (ViewState("LoadControls") == "true")
{
LoadControls();
}
}
This has the effect of then loading the control on-the-fly when the event first happens, and then at future times in the lifecycle.
I am developing a web application in asp.net and c#, now in a particular aspx page whenever I doubleClick(design view) on a button or on a drop down list, instead of going to
public void btn_click event or DropDown_SelectedIndexChanged event, the cursor points to protected void Page_Load only. Strange!! any remedy?
Not a fix for your VS misbehaving, if it is doing so. But this will help you wire up your events and perhaps notice anomalous event assignments:
Select the control in question, right-click>Properties, switch to the 'events' tab (lightning bolt) and either enter the name of a method or simply double click the empty space to generate an event handler in your codebehind.
This is also where you will see if Page_Load is already, for whatever reason, assigned to the event you are having trouble with.
HTH
May be both your btn_click event and DropDown_SelectedIndexChanged event delegates have Page_Load as the method. Check your events tab for button and dropdown.
this happens to me when I have my project running in debug mode and forget to stop it before editing my code. Long shot, but sometimes the obvious things are the things we overlook :)
I'm currently having a problem with what seems like the Timer_Tick event interfering with the event handling for other controls within the UpdatePanel.
For now I have a Countdown label and some buttons inside an UpdatePanel. The Timer is outside the UpdatePanel and its Tick event is registered as a trigger for the panel. On every Tick, the Countdown's Text property is modified.
Whenever a button is clicked, a pop-up box will appear. However, I notice that if I click the button just when a Tick occurs, nothing happens. I'm assuming that it is because the Click event does not register while the UpdatePanel is in the process of rendering its updated contents.
Should I be using another type of timer instead? Is there a way to force the Click event to interrupt the Tick event? Or are there other ways to fix this issue?
Thank you.
You can nest your UpdatePanels so that your Label has it's own UpdatePanel.