I have usercontrol x in a page, within usercontol x is usercontrol z. I need to do something to usercontrol z after an event fires in usercontrol x. I understand this is very generic, but it just lays out a simple premise for my issue.
Is there a simple way to get a list of all events that fire in the page lifecycle whether I am subscribed to them or not to find out what events fire between Event A on the page and Event B on control z? I would think that there would be something like this when page tracing is turned on, but I don't see any events listed. I imagine that it would be something that the pipeline could generate, maybe I could use reflection to get a list?
I found this topic hard to search against in general, maybe I am using bad keywords...
I did find an old project on codeproject.com, but I was hoping that there would be something more elegant available by now.
*To clarify, I'm looking to generate a list after a postback of every potential event (subscribed or not), in firing order from init to unload, of all controls on a page.
THIS POST: Tracing all events in VB.NET
gets me a little bit closer, however these are lists on a per control basis, not in chronological order.
Enable trace with <%# Page Trace="true" %> in page attribute. that should display life cycle events in sequence.
Well if you're just looking to see what the events are in general, and in what order they fire, check out this article. As far as getting them...well, that depends on what you mean. It could be as simple as getting them through reflection:
EventInfo[] events = this.GetType().GetEvents();
The ASP.NET Page Life Cycle Overview on MSDN lists all of the events fired by a Page from PreInit to Unload. Most of these events fire on any class that inherits from System.Web.UI.Control as well.
Update
Now that I understand your intention better, one possible solution would be to loop through the events of every control and assign an event handler that logs the calling of the event. There is at least one way to retrieve all of the event handlers assigned to an event, and it shouldn't be too difficult to adapt that code to assign an event handler instead.
Related
that is a question I have been asking myself for a while.
Giving a certain flow of events, can I when handling one of them, stop the next ones to be raised?
For example, when collapsing a node which child was selected in a treeview (winform), the events are raised like that:
BeforeCollapse
BeforeSelect
AfterSelect
AfterCollapse
I could stop them by using a class member, but I was wondering whether there was a built-in function or just another way (a more elegant way) to achieve this, by acting directly on the events queue.
Any idea?
Not easily, no. The order of the events firing is controlled by the TreeView control class, and there is no built-in way to prevent events from firing. But you have a couple of options:
Create your own TreeView class that inherits from the base class,
then add a bool property to prevent the events from processing.
Then you can override BeforeCollapse, etc. to check the bool
before calling base.BeforeCollapse.
Just create a bool flag, and check the flag in each of the events.
No there is no way to do that for that type of event (you are asking for TreeView).
Like for example could be managed KeyEventArgs.Handled via built-in mechanism.
You can use some instance (boolean ?) value to manage the flow,
or you can, unsubscribe from the event that you don't want more recieve, but after subscribe to it again. Sounds rough solution, but sometimes turns out reasonable one.
even if the event are raised nothing will happen if you don't bind an event handler to them. In this case you can just remove the handler using the code below:
object.Event -= new EventHandlerType(your_Method)
Otherwise you should create your own custom control
according to OnBeforeCollapse you get an TreeViewCancelEventArgs which has an Cancel property. Setting this to true should stop the flow, but will also not collapse it.
Same goes for OnBeforeSelect.
The only times you can easily "cancel" an event is if the event handler has the CancelEventHandler delegate type. Even then it doesn't really cancel it as much as set a flag for the remaining events that makes it skip performing all the events subscribed to it.
If you did have a CancelEventHandler type (which these don't) you'd simply set Cancel to true on the event object itself in the handler.
Plenty of other answers give you suggestions for what you should o. I'd just go with your idea: set a 'event cancelled' flag in your control class, and check it. When the last event in the series gets called, reset it.
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'm having an interesting lifecycle event error, imagine a code hierarchy like this:
Page 1
User Control 2
User Control 3
Where each of these items is a child in this order. I expect Page 1 to fire its oninit first, then User Control 2, then User Control 3. But this doesn't happen; actually, in this scenario, User Control 3 fires init first. I have each of these inheriting from a special base class, and have some plumbing code that needs to run in order. Any idea why this is happening?
Thanks.
What you're seeing isn't an error. It's happening because that's the way it's supposed to happen:
The Init event of individual
controls occurs before the Init
event of the page.
As pointed out by others, the Init events fire from the bottom up, while later events (such as Load) fire from the top down.
The general rule for how events are raised is that the initialization events are raised from the innermost control to the outermost one, and all other events are raised from the outermost control to the innermost one.
I'm setting a HTML string value to webbrowser.DocumentText. Problem is, sometimes it worked and sometimes it hangs up and not go through the documentcompleted event. what might be the problem?
Please reply, asap..
Thanks,
Jepe
Just a thought: With all the web-'dynam-ism' nowadays, a page is never really in a 'completely-loaded' state. After DocumentComplete, the OnLoad event of the page is fired, then any scripts placed in such an event are fired, and then javascript timers may be used to initiate download/upload of some resource, or a change in page using AJAX, etc.
I believe AJAX calls could cause all kinds of unseen problems with your WebBrowser control; because AJAX can cause multiple Navigating() events to fire during the loading of a page. And for that reason your app would experience multiple DocumentCompleted event fire on that page.
A possible solution could be to monitor the page changes and attempt to find out what possibly got changed. And to do this you may need to look into Notify method.
Called by MSHTML when a change occurs
in the contents of the markup
container with which it is
associated.
This and this discussion may help you coming up with something like following:
HtmlElement target = _webBrowser.Document.GetElementById("somedivthatwillbepopulatedbytheajaxrequest");
if (target != null)
{
target.AttachEventHandler("onpropertychange", new EventHandler(handler));
}
I'm experiencing a very strange problem...
I have a regular ASP.Net webpage with a page_init and a page_load function. It is my understanding(from everywhere I look) that page_init gets called on the first page load(as in, not ever called in a postback) and page_load is called anytime something happens with the page.(It is very hard finding any info about this except for dead links and stuff about the page life cycle)
Well, I have an update panel containing other update panels and other assorted controls. Anytime I edit one of these controls, an async postback happens but instead of only page_load being called, page_init is also called which isn't suppose to happen(and didn't happen before a big codebase change)
So I would like to know anything that might cause this behavior or just if my idea of how page events are called is wrong.
I think you have the wrong idea of the page load life cycle. The OnInit event is called on EVERY request. Having the Page_Init method in your code behind is a shorthand way of wiring up the pages OnInit event.
Now I believe that you are confusing this with the "IsPostBack" property which will be set to true if a page posts back to itself i.e. when you click a Button etc. My guess is what you need to do is add an if statement in your Page_Init method i.e.
if(!IsPostBack){
//Do something to to update the UI
}
Page_Init is definitely called on every page hit, postback or not, exactly the same as Page_Load.
The misconception that Page_Init doesn't get called on every request seems to be a common one.
Are you certain that this wasn't happening before your "big codebase change"?
My suggestion is that you create a simple example of what you're trying to do on a brand new scratch page based on these rules..
http://msdn.microsoft.com/en-us/library/ms178472.aspx
Keep adding complexity as you have it now until it breaks..
It would be difficult to diagnose your issue without the code..
Your Page_Init as well as Page_Load both methods should be called each time.