How to get the value of usercontrol to page holding usercontrol?
If I understand correctly, the problem is that you are trying to access the user control's StudentId property in page_load of the page that hosts the user control?
If that's the case, it is quite likely that you are just trying to read the data before the user control has fired the SelectedIndexChanged event on the dropdown list.
The simplest solution is to move the code that reads the property to the Page_PreRender event. This event happens late in the page life-cycle, and after all the user events have had a chance to fire off.
As an alternative, you can expose your own event (I'll call it "UserControlDropDownChanged") in the user control and have the code in your SelectedIndexChanged event handler fire the user control's UserControlDropDownChanged event. In your page, during page_load or page_init you'd register an event handler to listen to UserControlDropDownChanged from the user control... and in that event handler perform whatever functions you need to when the drop down list's value changes.
I provided an example of how to use events this way in response to another question here on SO if you aren't familiar with this technique.
You'll need to expose this value as a public property of the user control.
Related
Okay,
I have this scenario:
There is a user control with an update panel within it. There is a button within that update panel with proper postback trigger being set. The button_click event is also defined well. I need to call a full postback of the parent aspx page once the "button_click" event is completed. Under ideal case, all the form submission events such as postbacks occur before event based methods are executed. This means my page will first be reloaded then the button click event will be executed. I want something like to reverse this operation. First Button_click event execution then one postback after that on the aspx page(this page calls the user control-> and this user control has the updatepanel with button in it).
Any possible way out would be highly appreciated.
I don't think there's a way to change ASP.NET's lifecycle, like the one you described. A (dirty) way of postbacking the parent page is however to put a hidden button on that page, and call it via javascript in the UC. (via ScriptManager.RegisterStartupScript)
I want to prompt a message to the user Do You want to save the changes?? if he made some changes in any control on the current page before navigation to other page. what is the best way to do this. every control has their events. Like text-box key change event. combo box selectedItemChange event. But a lot of code have to be written in this scenario. I want this modification on each page of the project....
Thanks In Advance...
you'll atleast need to define the event handlers for the controls that can be changed.
Inside the event handlers you can just set a boolean variable to true, and check the value of the variable in OnNavigatedFrom method of the Page, and accordingly show the message.
If you use the Silverlight Navigation framework:
http://msdn.microsoft.com/en-us/library/cc838245(v=vs.95).aspx
There are events that get raised (navigating, navigated, etc...) where you can prompt the user and cancel the navigation.
my situation is a little complicated. What I'm trying to do is make reload UserControl (with dynamically changed control inside my UserControl). It's simple when I trying to do it OnInit or Page_Init event of my Page. But I need to do this inside a click event of button which by the way is ext.net type and have build in callback events.
So is there any way to invoke OnInit event of UserControl on event click raise?
If any more information needed pls feel free to ask in comments:)
Thanks for advance:)
I think you should manage this case differently.
OnInit is fired according to the webform life-cycle, in which each step has a specific purpose :
http://msdn.microsoft.com/en-us/library/ms178472(v=vs.100).aspx
During page initialization, controls on the page are available and
each control's UniqueID property is set. A master page and themes are
also applied to the page if applicable. If the current request is a
postback, the postback data has not yet been loaded and control
property values have not been restored to the values from view state.
You'd better not 'force' this concept, try to adapt your code to meet the flow constraints.
I am creating a custom control. Let's say I'm reinventing the wheel and creating a custom Button control that derives from the UserControl class(only for example)
Well, it of course has a Click event handler. Now my problem is, when do I call this event handler? I know it happens sometime between the Pages OnLoad and OnLoadComplete, but I'm not quite sure what event I can hookup to so that the Click event is raised at the same time as other control events.
When are you suppose to call custom control events?
In general you should raise the event as soon as you know that the underlying event has happened.
For example, how does the ASP.NET Button control know that the it was clicked by the use? It implements IPostBackEventHandler and the RaisePostBackEvent() method. That method will get called if there is postback event data associated with the control. I believe the association is determined by the "name" attribute that it renders. In RaisePostBackEvent() it then raises the Click event.
The question you need to answer is: How does your control know that it should raise its event? Once you find that our the rest is easy.
If your control has similarities to existing ASP.NET controls I would recommend stepping through the ASP.NET source code and seeing how those controls work.
If you implement IPostbackEventHandler, you can do something like this, taken from decompiling System.Web.Ui.WebControls.Button
protected virtual void RaisePostBackEvent(string eventArgument)
{
base.ValidateEvent(this.UniqueID, eventArgument);
if (this.CausesValidation)
{
this.Page.Validate(this.ValidationGroup);
}
this.OnClick(EventArgs.Empty);
this.OnCommand(new CommandEventArgs(this.CommandName, this.CommandArgument));
}
Say that I have a web user control that has several drop down lists in it. They are all set to AutoPostBack = true, BUT each SelectedIndexChanged event handler in my control will fire/chain the other SelectedIndexChanged handlers I have defined for the other DDLs. This means that when the user changes a single DDL, the event handlers are chained/fired for several other DDLs. The logic for which events are chained is very complicated, data driven, and can change depending on which list was actually changed by the user. Therefore, it is very difficult to determine which event handler would fire last.
From the page's point of view, I want to subscribe to a single SelectionChanged Event on the user control that will only fire one time per postback and not until all of the event handlers have fired. I don't care which event handlers have fired, only that the state of the control as a whole has changed.
I'm using C# 3.5/ASP.NET 2.0/VisualStudio 2008
How can I go about doing this?
EDIT: Moved clarification into original description. I think the fact that I specified AutoPostBack=true without specifying that chaining was happening was misleading. I apologize for the confusion.
It depends on when you need the event handler to fire in the page lifecycle.
Here's one strategy:
1) In your user control, track the selection changing of your dropdown lists. If the event handler is executed, update your local tracking variables.
2) In your usercontrol's PreRender handler, check your tracking variables and if called for, fire the user control's SelectionChangedEvent.
This strategy will guarantee that the event handling phase of the page lifecycle is done, but has the drawback that your main page won't receive the "SelectionChanged" on your user control until the PreRender phase. This may or may not work for your situation.
If you need to handle the SelectionChanged event for your usercontrol earlier, then you will likely have to put in more complicated tracking logic in your dropdownlist handlers, and add a tracking variable to ensure that the usercontrol's "SelectionChanged" event only ever gets fired once.
I think you need to create a delgate in child control and then reference that delegate into parent control.