When asp.net introduced the concept
of viewstate, it changed the way how developers maintain the state for the controls in a web page. Until then to keep the track
of the control(in classic asp), it was the developer responsibility to manually assign the posted content before rendering the
control again. Viewstate made allowed the developer to do it with ease. The developers are not bothered about how controls keep there state on post back. Viewstate is rendered to the browser as a hidden variable __viewstate. Since viewstate stores the values
of all controls, as the number
of controls in the page increases, the content
of viewstate grows large. It causes some websites to load slowly. As developers we need viewstate, but actually we do not want this for all the controls in the page. Till asp.net 3.5, if viewstate is disabled from web.config (using <pages viewstate=”false”/> ..</pages>), then you can not enable it from the
control level/page level. Both <%@ Page EnableViewState=”true”…. and <asp:textbox EnableViewState=”true” will not work in this case. Lot
of developers demands for more
control over viewstate. It will be useful if the developers are able to disable it for the entire page and enable it for only those controls that needed viewstate. With ASP.NET 4.0, this is possible, a happy news for the developers. This is achieved by introducing a new property called ViewStateMode. Let us see, What is ViewStateMode – Is a new property in asp.net 4.0, that allows developers to enable viewstate for individual
control even if the parent has disabled it. This ViewStateMode property can contain either
of three values Enabled- Enable view state for the
control even if the parent
control has view state disabled. Disabled - Disable view state for this
control even if the parent
control has view state enabled Inherit - Inherit the value
of ViewStateMode from the parent, this is the default value. To disable view state for a page and to enable it for a specific
control on the page, you can set the EnableViewState property
of the page to true, then set the ViewStateMode property
of the page to Disabled, and then set the ViewStateMode property
of the
control to Enabled. Find the example below. Page directive - <%@ Page Language="C#" EnableViewState="True" ViewStateMode="Disabled" .......... %> Code for the control - <asp:TextBox runat="server" ViewStateMode="Enabled" ............../> Now the viewstate will be disabled for the whole page, but enabled for the TextBox. ViewStateMode gives developers more
control over the viewstate.
