Page.IsPostBack Property
Updated: April 2009
Gets a value that indicates whether the page is being rendered for the first time or is being loaded in response to a postback.
Assembly: System.Web (in System.Web.dll)
'Declaration <BrowsableAttribute(False)> _ Public ReadOnly Property IsPostBack As Boolean 'Usage Dim instance As Page Dim value As Boolean value = instance.IsPostBack
Property Value
Type: System.Booleantrue if the page is being loaded in response to a client postback; otherwise, false.
For an explanation of the difference between postbacks and callbacks, see Implementing Client Callbacks Programmatically Without Postbacks in ASP.NET Web Pages.
| Topic | Location |
|---|---|
| How to: Determine How ASP.NET Web Pages Were Invoked | Building ASP .NET Web Applications |
| How to: Determine How ASP.NET Web Pages Were Invoked | Building ASP .NET Web Applications |
The following example shows how to test the value of the IsPostBack property when the page is loaded in order to determine whether the page is being rendered for the first time or is responding to a postback. If the page is being rendered for the first time, the code calls the Page.Validate method.
The page markup (not shown) contains RequiredFieldValidator controls that display asterisks if no entry is made for a required input field. Calling Page.Validate causes the asterisks as to be displayed immediately when the page is rendered, instead of waiting until the user clicks the Submit button. After a postback, it is not required to call Page.Validate, because that is part of the ordinary Page life cycle.
Windows 7, Windows Vista, Windows XP SP2, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP Starter Edition, Windows Server 2008 R2, Windows Server 2008, Windows Server 2003, Windows Server 2000 SP4, Windows Millennium Edition, Windows 98
The .NET Framework and .NET Compact Framework do not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.