What is ispostback how to use it

Getting Started with Visual Studio. When page get loaded, it is not postback. If your page contents some server controls and doesnot have client event fucntionality then, it causes postback.

Postback is actually sending all the information from client to server, server then process all those contents and returns back to client. This causes flicker to the client browser web page. When you refresh your page, it also causes postback. If you are moving from one page to another, then it is cross page postback and if you implement to call server side function from client, then it is called Callback and IsCallback event is raised.

So IsPostBack is used for checking full page refresh. IsPostBack is a property of the Asp. Net page that tells whether or not the page is on its initial load or if a user has perform a button on your web page that has caused the page to post back to itself. The content you requested has been removed. Ask a question. Quick access. Search related threads. Remove From My Forums. Answered by:. Stack Overflow for Teams — Collaborate and share knowledge with a private group.

Create a free Team What is Teams? Collectives on Stack Overflow. Learn more. IsPostBack how can use it Ask Question. Asked 10 years, 6 months ago. Active 10 years, 6 months ago. Viewed 13k times. What is this keyword how can use it? If Page. Tom Gullen Pathum Chamara Pathum Chamara 95 1 1 gold badge 2 2 silver badges 6 6 bronze badges. That's a bunch of keywords and a bunch of things that aren't keywords. The postback is a very basic and fundamental building block to asp. If you don't understand it, you won't have a grasp on any of the other material.

Wade I don't think that's entirely fair, I came from a long background of Classic ASP and such concepts that are fundamental blocks can be quite counter intuitive sometimes, but netherless this is an answer that could easily be googled. It was not meant to be harsh and I apologize if it was. Wade not at all wasn't Harsh, was just pointing out that some things are not so obvious to others : Your point is fair.

We know that all ASP. NET server controls retain their state across postback. These controls make use of ViewState. So, the first time, when the webform load. Now, when the client clicks the button control, and the webform is posted back to the server for processing. During the Page initialization, ViewState restoration happens. During this stage, the city names are retrieved from the viewstate and added to the DropDownList.

PageLoad event happens later in the life cycle of the webform. During page load we are again adding another set of cities.

Hence, the duplication. How to solve the DropDownList items duplication There are several ways to solve this. One of the best ways to do this, is to use IsPostBack property. That is, only if the webform is being loaded and accessed for the first time.

Now run the project, and the cities duplication issue is gone. But the problem, with this approach is that, the DropDownList list, does not remember your selecttion across postback. That is, Select "Mumabi" as the city, and submit the form. When the page rerenders, observer that selection is set back to "London".