What is a postback

Question

The best explanation I ve found for a postBack is from Wiki   a postback is an HTTP POST to the same page that the form is on   While the article does explain how a second page was needed in ASP  but no longer needed in ASP NET  it doesn t give much detail or background   I am looking for a freakin  tome of information on PostBacks  Much like the simple question of  how can I clean a house  can be addressed by this 900 page book  I don t need 900 pages worth  but details please  I found a nice little tutorial for ASP NET life cycle  but it seriously glosses over postbacks  amongst other things      I am looking to the developers who have been around before  NET and really don t take these kinds of things for granted  Books and hyperlinks are reasonable answers or additions to your answer

User · Answer

Postback is essentially when a form is submitted to the same page or script (.php .asp etc) as you are currently on to proccesses the data rather than sending you to a new page.

An example could be a page on a forum (viewpage.php), where you submit a comment and it is submitted to the same page (viewpage.php) and you would then see it with the new content added.

See: http://en.wikipedia.org/wiki/Postback

User · Answer

Postback happens when a webpage posts its data back to the same script dll whatever that generated the page in the first place   Example in C   asp net        if   IsPostback        generate form else    process submitted data

User · Answer

A post back is anything that cause the page from the client s web browser to be pushed back to the server   There s alot of info out there  search google for postbacks   Most of the time  any ASP control will cause a post back  button link click  but some don t unless you tell them to  checkbox combobox

User · Answer

Yet the question is answered accurately above  but just want to share my knowledge   Postback is basically a property that we can use while doing some tasks that need us to manage the state of the page  that is either we have fired some event for e g  a button click or if we have refreshed our page  When our page loads for the very first time   that is if we have refreshed our page  at that time postback-property is false  and after that it becomes true   if  ispostback        do some task here   else      do another task here     http   happycodng blogspot in 2013 09 concept-of-postback-in html

User · Answer

Yet the question is answered accurately above  but just want to share my knowledge   Postback is basically a property that we can use while doing some tasks that need us to manage the state of the page  that is either we have fired some event for e g  a button click or if we have refreshed our page  When our page loads for the very first time   that is if we have refreshed our page  at that time postback-property is false  and after that it becomes true   if  ispostback        do some task here   else      do another task here     http   happycodng blogspot in 2013 09 concept-of-postback-in html

User · Answer

The Wikipedia definition of postback is pretty good  but I d add the following  A postback is a subsequent HTTP POST to the same page that the form is on   If I have a page with a form on it and  rather than having my Submit button redirect the browser to another page that will process the form  instead have the Submit button refresh the current page  and perform some specific steps to validate save the page  presumably   then that Submit button is said to have posted back to the current page   Postbacks can be either full  refresh the entire page  or partial  in a case where AJAX is employed   A partial page postback will re-render only a part of the page  like a single drop-down list  a table  etc

User · Answer

A post back is anything that cause the page from the client s web browser to be pushed back to the server   There s alot of info out there  search google for postbacks   Most of the time  any ASP control will cause a post back  button link click  but some don t unless you tell them to  checkbox combobox

User · Answer

The term is also used in web application development when interacting with 3rd party web-service APIs  Many APIs require  both an interactive and non-interactive integration  Typically the interactive part is done using redirects  site 1 redirects a user to site 2  where they sign in  and are redirected back   The non-interactive part is done using a  postback   or an HTTP POST from site 2 s servers to site 1 s servers

User · Answer

POSTBACK  Part of ASP NET s contrived technique for hiding the true stateless nature of the web HTTP behind a stateful facade   This results in complex code  IsPostback        a hard to understand page lifecycle  many different events      and numerous problems  ViewState size  web-farm stickyness  state servers  browser warnings  not using PRG pattern            See ASP NET MVC instead

User · Answer

A post back is anything that cause the page from the client s web browser to be pushed back to the server   There s alot of info out there  search google for postbacks   Most of the time  any ASP control will cause a post back  button link click  but some don t unless you tell them to  checkbox combobox

User · Answer

IsPostBack is a property of the Asp Net page that tells whether or not the page is on its initial load and if a user has perform a button on your web page that has caused the page to post back to itself    more on     Asp Net ispostback

User · Answer

When a script generates an html form and that form s action http POSTs back to the same form

User · Answer

Postback happens when a webpage posts its data back to the same script dll whatever that generated the page in the first place   Example in C   asp net        if   IsPostback        generate form else    process submitted data

User · Answer

Expanding on the definitions given  the most important thing you need to know as a web-developer is that NO STATE IS SAVED between postbacks  There are ways to retain state  such as the Session or Viewstate collections in ASP NET  but as a rule of thumb write your programs where you can recreate your state on every postback   This is probably the biggest difference between desktop and web-based application programming  and took me months to learn to the point where I was instinctively writing this way

User · Answer

Postback refers to HTML forms  An HTML form has 2 methods  GET and POST  These methods determine how data is sent from the client via the form  to the server  A Postback is the action of POSTing back to the submitting page  In essence  it forms a complete circuit from the client  to the server  and back again

User · Answer

From wikipedia      A Postback is an action taken by an   interactive webpage  when the entire   page and its contents are sent to the   server for processing some information   and then  the server posts the same   page back to the browser

User · Answer

Postback is a request during which ASP restores values of controls  properties from view state

User · Answer

When a script generates an html form and that form s action http POSTs back to the same form

User · Answer

From wikipedia      A Postback is an action taken by an   interactive webpage  when the entire   page and its contents are sent to the   server for processing some information   and then  the server posts the same   page back to the browser

User · Answer

Postback refers to HTML forms  An HTML form has 2 methods  GET and POST  These methods determine how data is sent from the client via the form  to the server  A Postback is the action of POSTing back to the submitting page  In essence  it forms a complete circuit from the client  to the server  and back again

User · Answer

Expanding on the definitions given  the most important thing you need to know as a web-developer is that NO STATE IS SAVED between postbacks  There are ways to retain state  such as the Session or Viewstate collections in ASP NET  but as a rule of thumb write your programs where you can recreate your state on every postback   This is probably the biggest difference between desktop and web-based application programming  and took me months to learn to the point where I was instinctively writing this way

User · Answer

Postback refers to HTML forms  An HTML form has 2 methods  GET and POST  These methods determine how data is sent from the client via the form  to the server  A Postback is the action of POSTing back to the submitting page  In essence  it forms a complete circuit from the client  to the server  and back again

User · Answer

Web developement generally involves html pages that hold forms   lt form gt  tags    Forms post to URLs  You can set a given form to post to any url you want to   A postback is when a form posts back to it s own page url     The term has special significance for ASP Net developers  because it is the primary mechanism that drives a lot of the behavior for a page -- specifically  event handling    ASP Net pages have exactly one server form that nearly always posts back to itself  and these post backs trigger execution on the server of something called the Page Lifecycle

User · Answer

Simply put this by a little code  Hope it is helpful to you  When you firstly request the page url  you can view the source code of it in most browser  Below is a sample of it    The essential of Post Back is actually call the   doPostBack which submit all the form data got from your firstly requested back to the server     EVENTTARGET contains the id of the control     lt html xmlns  http   www w3 org 1999 xhtml  gt   lt head gt  lt title gt      NHibernate Demo  lt  title gt       lt script language  javascript  type  text javascript  gt          function dopost                       doPostBack  LinkButton1                           lt  script gt   lt  head gt   lt body gt       lt h1 gt NHibernate Demo lt  h1 gt           lt form name  ctl01  method  post  action  Default aspx  id  ctl01  gt   lt div gt   lt input type  hidden  name    EVENTTARGET  id    EVENTTARGET  value      gt   lt input type  hidden  name    EVENTARGUMENT  id    EVENTARGUMENT  value      gt   lt input type  hidden  name    VIEWSTATE  id    VIEWSTATE  value   wEPDwUKLTMxNzcwNTYyMWRkKHoXAC3dty39nROvcj1ZHqZ5FYY     gt   lt  div gt    lt script type  text javascript  gt     lt   CDATA  var theForm   document forms  ctl01    if   theForm        theForm   document ctl01    function   doPostBack eventTarget  eventArgument        if   theForm onsubmit     theForm onsubmit      false             theForm   EVENTTARGET value   eventTarget          theForm   EVENTARGUMENT value   eventArgument          theForm submit                 gt   lt  script gt      lt div gt       lt input type  hidden  name    VIEWSTATEGENERATOR  id    VIEWSTATEGENERATOR  value  B2D7F301    gt       lt input type  hidden  name    EVENTVALIDATION  id    EVENTVALIDATION  value   wEWAwKZx5vTCgKM54rGBgLM9PumD20dn9KQguomfpAOdTG0r9Psa7al    gt   lt  div gt           lt a id  LinkButton1  href  javascript   doPostBack  LinkButton1       gt LinkButton lt  a gt           lt input type  button  value  testPostBack  id  testpostback  onclick  dopost       gt       lt  form gt   lt  body gt   lt  html gt

User · Answer

Expanding on the definitions given  the most important thing you need to know as a web-developer is that NO STATE IS SAVED between postbacks  There are ways to retain state  such as the Session or Viewstate collections in ASP NET  but as a rule of thumb write your programs where you can recreate your state on every postback   This is probably the biggest difference between desktop and web-based application programming  and took me months to learn to the point where I was instinctively writing this way

User · Answer

Postback happens when a webpage posts its data back to the same script dll whatever that generated the page in the first place   Example in C   asp net        if   IsPostback        generate form else    process submitted data

User · Answer

From wikipedia      A Postback is an action taken by an   interactive webpage  when the entire   page and its contents are sent to the   server for processing some information   and then  the server posts the same   page back to the browser

User · Answer

Postback happens when a webpage posts its data back to the same script dll whatever that generated the page in the first place   Example in C   asp net        if   IsPostback        generate form else    process submitted data

User · Answer

Postback is essentially when a form is submitted to the same page or script (.php .asp etc) as you are currently on to proccesses the data rather than sending you to a new page.

An example could be a page on a forum (viewpage.php), where you submit a comment and it is submitted to the same page (viewpage.php) and you would then see it with the new content added.

See: http://en.wikipedia.org/wiki/Postback

User · Answer

Web developement generally involves html pages that hold forms   lt form gt  tags    Forms post to URLs  You can set a given form to post to any url you want to   A postback is when a form posts back to it s own page url     The term has special significance for ASP Net developers  because it is the primary mechanism that drives a lot of the behavior for a page -- specifically  event handling    ASP Net pages have exactly one server form that nearly always posts back to itself  and these post backs trigger execution on the server of something called the Page Lifecycle

User · Answer

Web developement generally involves html pages that hold forms   lt form gt  tags    Forms post to URLs  You can set a given form to post to any url you want to   A postback is when a form posts back to it s own page url     The term has special significance for ASP Net developers  because it is the primary mechanism that drives a lot of the behavior for a page -- specifically  event handling    ASP Net pages have exactly one server form that nearly always posts back to itself  and these post backs trigger execution on the server of something called the Page Lifecycle

User · Answer

In the old HTML  the only way to make something updated on the webpage is to resend a new webpage to the client browser  That s what ASP used to do  you have to do this thing call a  PostBack  to send an updated page to the client   In ASP  NET  you don t have to resend the entire webpage  You can now use AJAX  or other ASP NET controls such that you don t have to resend the entire webpage   If you visit some old website  you would notice that once you click something  the entire page has to be refresh  this is the old ASP   In most of the modern website  you will notice your browser doesn t have to refresh the entire page  it only updates the part of the content that needs to be updated  For example  in Stackoverflow  you see the page update only the content  not the entire webpage

User · Answer

Postback is essentially when a form is submitted to the same page or script (.php .asp etc) as you are currently on to proccesses the data rather than sending you to a new page.

An example could be a page on a forum (viewpage.php), where you submit a comment and it is submitted to the same page (viewpage.php) and you would then see it with the new content added.

See: http://en.wikipedia.org/wiki/Postback

User · Answer

The following is aimed at beginners to ASP Net      When does it happen   A postback originates from the client browser  Usually one of the controls on the page will be manipulated by the user  a button clicked or dropdown changed  etc   and this control will initiate a postback  The state of this control  plus all other controls on the page  known as the View State  is Posted Back to the web server   What happens   Most commonly the postback causes the web server to create an instance of the code behind class of the page that initiated the postback  This page object is then executed within the normal page lifecycle with a slight difference  see below   If you do not redirect the user specifically to another page somewhere during the page lifecycle  the final result of the postback will be the same page displayed to the user again  and then another postback could happen  and so on   Why does it happen   The web application is running on the web server  In order to process the user   s response  cause the application state to change  or move to a different page  you need to get some code to execute on the web server  The only way to achieve this is to collect up all the information that the user is currently working on and send it all back to the server   Some things for a beginner to note are      The state of the controls on the posting back page are available within the context  This will allow you to manipulate the page controls or redirect to another page based on the information there  Controls on a web form have events  and therefore event handlers  just like any other controls  The initialisation part of the page lifecycle will execute before the event handler of the control that caused the post back  Therefore the code in the page   s Init and Load event handler will execute before the code in the event handler for the button that the user clicked  The value of the    Page IsPostBack    property will be set to    true    when the page is executing after a postback  and    false    otherwise  Technologies like Ajax and MVC have changed the way postbacks work

User · Answer

The term is also used in web application development when interacting with 3rd party web-service APIs  Many APIs require  both an interactive and non-interactive integration  Typically the interactive part is done using redirects  site 1 redirects a user to site 2  where they sign in  and are redirected back   The non-interactive part is done using a  postback   or an HTTP POST from site 2 s servers to site 1 s servers

User · Answer

A post back is round trip from the client  Browser  to the server and then back to the client     This enables you page to go through the asp engine on the server and any dynamic content to be updated    here is a nice explanation

User · Answer

The following is aimed at beginners to ASP Net      When does it happen   A postback originates from the client browser  Usually one of the controls on the page will be manipulated by the user  a button clicked or dropdown changed  etc   and this control will initiate a postback  The state of this control  plus all other controls on the page  known as the View State  is Posted Back to the web server   What happens   Most commonly the postback causes the web server to create an instance of the code behind class of the page that initiated the postback  This page object is then executed within the normal page lifecycle with a slight difference  see below   If you do not redirect the user specifically to another page somewhere during the page lifecycle  the final result of the postback will be the same page displayed to the user again  and then another postback could happen  and so on   Why does it happen   The web application is running on the web server  In order to process the user   s response  cause the application state to change  or move to a different page  you need to get some code to execute on the web server  The only way to achieve this is to collect up all the information that the user is currently working on and send it all back to the server   Some things for a beginner to note are      The state of the controls on the posting back page are available within the context  This will allow you to manipulate the page controls or redirect to another page based on the information there  Controls on a web form have events  and therefore event handlers  just like any other controls  The initialisation part of the page lifecycle will execute before the event handler of the control that caused the post back  Therefore the code in the page   s Init and Load event handler will execute before the code in the event handler for the button that the user clicked  The value of the    Page IsPostBack    property will be set to    true    when the page is executing after a postback  and    false    otherwise  Technologies like Ajax and MVC have changed the way postbacks work

User · Answer

Web developement generally involves html pages that hold forms   lt form gt  tags    Forms post to URLs  You can set a given form to post to any url you want to   A postback is when a form posts back to it s own page url     The term has special significance for ASP Net developers  because it is the primary mechanism that drives a lot of the behavior for a page -- specifically  event handling    ASP Net pages have exactly one server form that nearly always posts back to itself  and these post backs trigger execution on the server of something called the Page Lifecycle

User · Answer

The following is aimed at beginners to ASP Net      When does it happen   A postback originates from the client browser  Usually one of the controls on the page will be manipulated by the user  a button clicked or dropdown changed  etc   and this control will initiate a postback  The state of this control  plus all other controls on the page  known as the View State  is Posted Back to the web server   What happens   Most commonly the postback causes the web server to create an instance of the code behind class of the page that initiated the postback  This page object is then executed within the normal page lifecycle with a slight difference  see below   If you do not redirect the user specifically to another page somewhere during the page lifecycle  the final result of the postback will be the same page displayed to the user again  and then another postback could happen  and so on   Why does it happen   The web application is running on the web server  In order to process the user   s response  cause the application state to change  or move to a different page  you need to get some code to execute on the web server  The only way to achieve this is to collect up all the information that the user is currently working on and send it all back to the server   Some things for a beginner to note are      The state of the controls on the posting back page are available within the context  This will allow you to manipulate the page controls or redirect to another page based on the information there  Controls on a web form have events  and therefore event handlers  just like any other controls  The initialisation part of the page lifecycle will execute before the event handler of the control that caused the post back  Therefore the code in the page   s Init and Load event handler will execute before the code in the event handler for the button that the user clicked  The value of the    Page IsPostBack    property will be set to    true    when the page is executing after a postback  and    false    otherwise  Technologies like Ajax and MVC have changed the way postbacks work

User · Answer

When a script generates an html form and that form s action http POSTs back to the same form

User · Answer

ASP Net uses a new concept  well  new compared to asp    it s antiquated now  of ViewState to maintain the state of your asp net controls   What does this mean   In a nutshell  if you type something into a textbox or select a dropdown from a dropdownlist  it will remember the values when you click on a button   Old asp would force you to write code to remember these values   This is useful when if a user encounters an error   Instead of the programmer having to deal with remembering to re-populate each web control  the asp net viewstate does this for you automatically   It s also useful because now the code behind can access the values of these controls on your asp net web form with intellisense   As for posting to the same page  yes  a  submit  button will post to an event handler on the code behind of the page   It s up to the event handler in the code behind to redirect to a different page if needs be  or serve up an error message to your page or whatever else you might need to do

User · Answer

The following is aimed at beginners to ASP Net      When does it happen   A postback originates from the client browser  Usually one of the controls on the page will be manipulated by the user  a button clicked or dropdown changed  etc   and this control will initiate a postback  The state of this control  plus all other controls on the page  known as the View State  is Posted Back to the web server   What happens   Most commonly the postback causes the web server to create an instance of the code behind class of the page that initiated the postback  This page object is then executed within the normal page lifecycle with a slight difference  see below   If you do not redirect the user specifically to another page somewhere during the page lifecycle  the final result of the postback will be the same page displayed to the user again  and then another postback could happen  and so on   Why does it happen   The web application is running on the web server  In order to process the user   s response  cause the application state to change  or move to a different page  you need to get some code to execute on the web server  The only way to achieve this is to collect up all the information that the user is currently working on and send it all back to the server   Some things for a beginner to note are      The state of the controls on the posting back page are available within the context  This will allow you to manipulate the page controls or redirect to another page based on the information there  Controls on a web form have events  and therefore event handlers  just like any other controls  The initialisation part of the page lifecycle will execute before the event handler of the control that caused the post back  Therefore the code in the page   s Init and Load event handler will execute before the code in the event handler for the button that the user clicked  The value of the    Page IsPostBack    property will be set to    true    when the page is executing after a postback  and    false    otherwise  Technologies like Ajax and MVC have changed the way postbacks work

User · Answer

A post back is anything that cause the page from the client s web browser to be pushed back to the server   There s alot of info out there  search google for postbacks   Most of the time  any ASP control will cause a post back  button link click  but some don t unless you tell them to  checkbox combobox

User · Answer

From wikipedia      A Postback is an action taken by an   interactive webpage  when the entire   page and its contents are sent to the   server for processing some information   and then  the server posts the same   page back to the browser

User · Answer

Postback is essentially when a form is submitted to the same page or script (.php .asp etc) as you are currently on to proccesses the data rather than sending you to a new page.

An example could be a page on a forum (viewpage.php), where you submit a comment and it is submitted to the same page (viewpage.php) and you would then see it with the new content added.

See: http://en.wikipedia.org/wiki/Postback

User · Answer

Expanding on the definitions given  the most important thing you need to know as a web-developer is that NO STATE IS SAVED between postbacks  There are ways to retain state  such as the Session or Viewstate collections in ASP NET  but as a rule of thumb write your programs where you can recreate your state on every postback   This is probably the biggest difference between desktop and web-based application programming  and took me months to learn to the point where I was instinctively writing this way

User · Answer

So far I ve seen the right answer alluded to repeatedly  and almost everyone has come shy of what I consider subjectively to be the mark   Let s start with the basics   An HTTP request can be any of the HTTP verbs  but the two that people use most are GET and POST  Well  those are the two a programmer uses most frequently  The others all have some purpose  if they re implemented on the server  When you send information to the server  you can do so either through the use of the URL  to request a page  or within the body of the request  POST  PUT  DELETE  for instance    Now you ll remark  I m sure  that the URL in a GET request often contains data  and this is true  but according to W3C  you should not use GET to alter state  and yet we do often  It s sort of a hack that we all agree is an actual use  and not a hack  Whether that makes it a hack or an actual implementation detail I leave up to you   So when you send the body of the POST  skipping the others for now  you can figure it out from here  with the form elements  you re sending back certain elements  How those elements are defined is up to you and to the environment you re working in  You could post to a server with a JSON element in the body  or with XML  or with form fields  Generally we do posts from a FORM element in the body of the HTML   Now everyone says   oh  a postback is a subsequent request to a page   But  that s not true  A postback is when you send data via POST -  back to the server  I say this because the difference between a GET request and a POST request is if data is included in the body  and the verb used  but the client usually knows how to deal with that   You could postback to the page on the first time the page is visited  and in fact ASP NET has tools for doing that in the library  You could certainly have a desktop client POST data to a server  think Twitter  without showing any webpage at all from the server  ok  so twitter is probably not the best concept to use for an example here  but I want to illustrate that you can use a client that doesn t show the webpage  so no request is necessary    So really what you should read there in  postback  is  I m POSTing data BACK to the server for processing   It s presumed that you retrieved the page initially with a GET to show the user the  lt form gt  element that has  lt input gt  fields for them to interact with  and that at the end you re sending data back  But I hope you can see that it doesn t have to be in that order   So here s something else to consider   What if you gave the user a page with a bunch of  lt input gt s and no  lt form gt  but instead  had a button wired up in javascript to concat all those  lt input gt s with  amp value-n  and send them as a GET  Does the same thing  but violates that concept of only using GET for requests   possibly  ensuing discussion encourages me to reinforce that GET should have no side effects  no updating values   It s how come you can send someone a link to a google search  for instance  So we don t ALWAYS have to POST BACK to the server to get data   Hope this helps  Cheers

User · Answer

See ASP NET Page Life Cycle Overview on MSDN for a good general introduction about what happens when a requests hits the server   A PostBack is any request for a page that is not the first request  A PostBack will always be in response to a user action  triggered most commonly by a Button  AutoPostBack control or Ajax

User · Answer

When a script generates an html form and that form s action http POSTs back to the same form

User · Answer

Postback refers to HTML forms  An HTML form has 2 methods  GET and POST  These methods determine how data is sent from the client via the form  to the server  A Postback is the action of POSTing back to the submitting page  In essence  it forms a complete circuit from the client  to the server  and back again

[asp.net] What is a postback?

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