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.
Related
I am reading the textbook "Sams ASP.NET 4 unleashed" and I am confused about the Difference between TextChanged property and AutoPostBack property with respect to ASP.NET TextBox control.
The book explains the two properties as :
AutoPostBack—Enables you to post the form containing the TextBox back
to the server automatically when the contents of the TextBox is
changed.
then,
TextChanged—Raised on the server when the contents of the text box are
changed.
Then it continues to explain :
When the AutoPostBack property has the value True, the form containing
the TextBox is automatically posted back to the server when the
contents of the TextBox changes. If you modify the contents of the
text box and tab out of the TextBox control, the form is automatically
posted back to the server, and the contents of the TextBox display.
The line that confused me is this one :
You can handle TextChanged event even when you don’t use the
AutoPostBack property.
Well, what is the difference between Autopostback property and textchanged property of both cause the page to be posted again to the server? Or is it that the working of both the methods differ from each other? I am confused..please help me understand it better.
You can handle TextChanged event even when you don’t use the AutoPostBack property.
Yes, that's true. You can handle the TextChanged event on the next roundtrip to the server even if it doesn't post back immediately.
So when you handle the event and AutoPostBack is set to true, the postback will happen immediately and the TextChanged-event is raised.
When AutoPostBack is set to false, you can handle the event anyway on the next postback(f.e. a button-click)
what is the difference between Autopostback property and textchanged property of both cause the page to be posted again to the server?
So the bold printed is simply wrong.
The difference is that the one controls the postback-behaviour and the other registers an event handler.
TextChanged will be raised when postback is completed and directed to self page. After Load cycle this event is raised. Which means that TextChanged is raising between two postbacks.
AutoPostBack property is activating postback, when content of textbox is changed and focused out from this textbox. After that postback occurs, page is directed to self. Then again after Load cycle TextChanged event is raised.
Also TextChanged is an 'event' not property.
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.
can you define autopostback and postback and it's differences and which web server control support autopostback and postback and also the difference between postback and callback?
postback: the page performs a POST request to itself
autopostback: a postback is performed automatically, for example when the selected value of a dropdown changes
callback: a method which is invoked when a certain event occurs such as clicking on a button. It also could have another meaning that a page performs a request back to the server (such as an AJAX request).
A postback is initiated by the browser, and reloads the whole page, usually when a control on the page (e.g. a button) is changed.
With some controls (e.g. Checkboxes), you choose if changing the control should result in a postback. This property is called AutoPostback.
A callback is initiated by java script in the page, and can load/update parts of the page, e.g. by manipulating the DOM.
Controls that support AutoPostback includes:
List item
ListControl
BulletedList
CheckBoxList
DropDownList
ListBox
RadioButtonList
CheckBox
TextBox
PostBack happens when data is send to the server (he page performs a POST request to itself)
IsPostBack helps you to identify if postback happen or not
Autopostback if this property of control is true helps to you post as soon as data change on the contol or some event occur
callback is a special postback, so a round-trip always occurs; however, unlike the classic postback, the script callback doesn't redraw the whole page. ViewState is not updated during a callback, it is for postback.
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 a GridView control where if the user click on the auto-generated edit button. A window will pop up using modal pop-up extender with a drop down list for user to select. The problem is the SelectedIndexChanged event will not fire if AutoPostBack is set to false.
But if I set the AutoPostBack to true the pop-up will go away without firing the SelectedIndexChanged event.
Is it possible to have a control with AutoPostBack set to true inside the modal pop-up?
Please put below code on drop down server side change event
modalpopup.show();
updatepanel.update();
where modalpopup is "ID" of modalpopupextender
and updatepanel is "ID" of updatepanel
The problem is the selectedindexchange
event will not fire if autopostback is
set to false...
I'm not sure that statement is strictly true. Isn't it a case that if autopostback is false, the SelectedIndexChange event fires during the next postback? So if you change the index, then click a Submit button, that's when the index change event is fired.
This isn't much good if you need server code to run to respond to the index change while the popup is still showing, but otherwise, you can still respond to the index change.
If you need to change something in the popup in response to the index change, you can always use client-side javascript.
You can use an UpdatePanel to resolve this problem. Wrap the DropDownList and any other controls that might give similar issue inside of an UpdatePanel, inside of the pop-up control. This will allow the pop-up to continue showing, while executing your postback code at the right time.