I have a dropdownlist, in the client side, i have it's on change event. If validation is passed, it's selected inded changed event should be fired(server side). My side, the server event is not getting fired. Autopostback is also set is true.
Any suggestion ?
If you are adding the code from the code-behind (as opposed to in the ASPX or ASCX markup), make sure you add it in the Page_Init event or override CreateChildControls. If you want until the Page_Load event to add it, the ASP.NET has already initialized the control state and view state and then will not be aware that the dropdown exists, so when the postback comes it won't know what control to route it to.
Also, in this case, make sure you are always adding the control to the page, not just when Page.IsPostback==false
Make sure your page code is in autoeventwireup = true.
you can check it in your page design page on top.
if autoeventwireup is set to false your event doesn't fire. auto event will set automatically event so it is necessary to write else you have to set event on initialize state.
Related
What's the difference between AutoPostBack=True and AutoPostBack=False?
Taken from http://www.dotnetspider.com/resources/189-AutoPostBack-What-How-works.aspx:
Autopostback is the mechanism by which the page will be posted
back to the server automatically based on some events in the web controls. In some of the web controls, the property called auto post back, if set to true, will send the request to the server when an event happens in the control.
Whenever we set the autopostback attribute to true on any of the controls, the .NET framework will automatically insert a few lines of code into the HTML generated to implement this functionality.
A JavaScript method with name __doPostBack (eventtarget, eventargument)
Two hidden variables with name __EVENTTARGET and __EVENTARGUMENT
OnChange JavaScript event to the control
AutoPostBack = true permits control to post back to the server. It is associated with an Event.
Example:
<asp:DropDownList id="id" runat="server" AutoPostBack="true" OnSelectIndexChanged="..."/>
The aspx page with the above drop down list does not need an asp:button to do the post back. When you change an option in the drop down list, the page gets posted back to the server.
Default value of AutoPostBack on control is false.
AutopostBack is a property which you assign to web controls if you want to post back the page when any event occurs at them.
You may see this article: What is AutoPostBack?
Autopostback is the mechanism, by which the page will be posted back
to the server automatically based on some events in the web controls.
In some of the web controls, the property called auto post back, which
if set to true, will send the request to the server when an event
happens in the control
For example, TextBox has AutoPostBack property
Use the AutoPostBack property to specify whether an automatic postback
to the server will occur when the TextBox control loses focus.
Pressing the ENTER or the TAB key while in the TextBox control is the
most common way to change focus.
The AutoPostBack property is used to set or return whether or not an automatic postback occurs when the user presses "ENTER" or "TAB" in the TextBox control.
If this property is set to TRUE the automatic postback is enabled, otherwise FALSE. The default is FALSE.
There is one event which is default associate with any webcontrol. For example, in case of Button click event, in case of Check box CheckChangedEvent is there. So in case of AutoPostBack true these events are called by default and event handle at server side.
AutopostBack :
AutopostBack is a property of the controls which enables the post back on the changes of the web control.
Difference between AutopostBack=True and AutoPostBack=False:
If the AutopostBack property is set to true, a post back is sent immediately to the server
If the AutopostBack property is set to false, then no post back occurs.
AutoPostBack property:
Asp.net controls which cannot submit the Form (PostBack) on their own and
hence ASP.Net has provided a feature using
AutoPostBack = "true"
: which controls like DropDownList, CheckBoxList, RadioButtonList, etc. can perform PostBack(when clicked on it).
And
AutoPostBack = "false"
It is the by default state of controls which can perform Postback on button submit.
hai sir
There is one event which is default associate with any webcontrol.
For example, in case of Button click event, in case of Check box
CheckChangedEvent is there. So in case of AutoPostBack true these
events are called by default and event handle at server sid
If you want a control to postback automatically when an event is raised, you need to set the AutoPostBack property of the control to True.
I have two radio button on my asp.net page, with AutoPostBack = True
When I click on either of those, they each set a flag SaveData=False
However, when I click on them, the page_load event occurs first, so the page_load event saves the data, then the radiobutton_OnCheckedChanged event is triggered.
How can I trigger the OnCheckedChanged before the page_load event?
You can't.
You need to read up on the page lifecycle.
You can't trigger the OnCheckedChanged before radiobutton_OnCheckedChanged because that's the normal page life cycle.
You can check in Page_Load if Page.IsPostBack is true or not, and then don't save (or save) the data.
Troy - you will have to take care of this on the client side (javascript / jquery).
Your AutoPostBack = True causes the form to do a postback which calls page load.
Its all about how the page lifecycle and server side events work.
You can't the page always needs to load before events can be fired. This has to do with control creation, view state management, control state, etc.
What you want to do in your Page_Load is something like:
if(!this.IsPostBack)
{
// Do the stuff you want on the initial page load
}
Anything that you do not want to happen when the radio buttons are clicked, put it inside the if {} block. IsPostBack indicates that the page is processing a post-back event, which is what happens when you click one of your radio buttons.
You can't change the order/sequence of event handler execution. However you may move the code inside the page_load to another event handler.
I forgot to mention this asp.net 2.0.
The user control has a unique id and it is loaded in the PageLoad event.
The user control is loaded into a panel and the panel is inside of a webpart.
The dropdown has autopostback set to true.
EnableViewState = true on the dropdown.
The ListItems are created in the dropdowns pre-render event method.
This is why I don't understand why it is not firing, the dropdown is the only thing that causes postback on this user control.
The event methods for the dropdown should occur since the user control is loaded in the page load method on postback again right?
Make sure there is no OnLoad or PageLoad event that is rebinding the datasource of the dropdown list. Rebinding the data with a new set of data may cause the clickhandler to not ever get executed.
make sure you have if (!Page.IsPostBack) around dropdownlist.datasource = and dropdownlist.databind()
I am not sure if this is your problem, but it is the most common.
Try with EnableViewState set to
true for the DropDownList
If the ViewState is set to false, on post back the selected Index gets back to default which is normally the first Item. First item, if selected, does not cause SelectedIndexChange event to fire
I have an update panel that contains a repeater that calls a user control into each row. When I click a button inside the user control, the page does not refresh at all, only when I reload it completely. How can I make the update panel refresh from user control's button click?
Phairoh is correct that your button needs to successfully cause a PostBack.
There are three things that affect when a UpdatePanel is updated:
The UpdateMode property - This takes two possible values, Always and Conditional.
If it is set to Always then any postback o the page will cause the UpdatePanel to update.
If it is set to Conditional then the UpdatePanel is only updated when the UpdatePanel's Update method is called or when one of the UpdatePanel's triggers does a postback.
The Triggers proroperty - Defines which controls will cause the UpdatePanel to be updated when UpdateMode is set to Conditional.
The ChildrenAsTriggers property - This is a boolean value that determines if child controls of the UpdatePanel are automatically considered triggers without having to be added to the Triggers collection.
Because your button is in a UserControl it won't be easy to add the control to the Triggers collection or to have the button call the Update method on the UpdatePanel that is not inside the UserControl.
Because your UpdatePanel contains the UserControl's your best bet is to enable ChildrenAsTriggers. If this doesn't work try setting the UpdateMode property to Always. If this still doesn't work then Phairoh is probably correct and your Button isn't posting back.
Sometimes solving this problem not really convenient with Triggers. So here is another fancy approach which could be used even from your user controls without any knowledge about Update Panel:
var scriptManager = ScriptManager.GetCurrent(Page);
if (scriptManager != null)
scriptManager.RegisterPostBackControl(SomeControlID);
Are you sure your buttons on your user control are attempting to do a postback? I haven't used update panels in a while (and I'd actually recommend avoiding them) but if I recall correctly they will refresh whenever a postback is done within them. This means that your buttons must be Asp:Buttons (or similar controls that cause postback) and not have some kind of javascript on them that would not allow their action to continue (such as a return false).
I have a ListView inside of an Update Panel and wanted to change the Select Query from the code behind fired by a button click event and then reload the ListView inside of the Update Panel. Does anyone know how to cause the Update Panel to refresh from the code behind?
Just do:
YourUpdatePanelId.Update();
From MSDN:
If the page is enabled for partial-page rendering, when you invoke the Update method, the UpdatePanel control's content is updated in the browser. Call the Update method if you have server code that must execute to determine whether an UpdatePanel control should be updated. If you plan to use the Update method, set the UpdateMode property to Conditional. If you want the decision to update the panel to be determined in server logic, make sure that the ChildrenAsTriggers property is false and that no explicit triggers are defined for the panel.
In a typical page development scenario, if you define triggers or if the ChildrenAsTriggers property is true for the UpdatePanel control, the Update method is automatically called during the page life cycle.
If the ContentTemplate property is not defined for the UpdatePanel control, no updates of the panel will occur.