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The PreRender Event

By handling this event, pages and controls can perform any updates before the output is rendered. The PreRender event fires for the page first and then recursively for all controls. Note that at this time the page ensures that all child controls are created. This step is important, especially for composite controls.

The PreRenderComplete Event

Because the PreRender event is recursively fired for all child controls, there’s no way for the page author to know when the pre-rendering phase has been completed. For this reason, ASP.NET supports an extra event raised only for the page. This event is PreRenderComplete.

The SaveStateComplete Event

The next step before each control is rendered out to generate the markup for the page is saving the current state of the page to the view-state storage medium. Note that every action taken after this point that modifies the state could affect the rendering, but it is not persisted and won’t be retrieved on the next postback. Saving the page state is a recursive process in which the page processor walks its way through the whole page tree, calling the SaveViewState method on constituent controls and the page itself. SaveViewState is a protected and virtual (that is, overridable) method that is responsible for persisting the content of the ViewState dictionary for the current control. (We’ll come back to the ViewState dictionary in Chapter 19.)

ASP.NET server controls can provide a second type of state, known as a “control state.” A control state is a sort of private view state that is not subject to the application’s control. In other words, the control state of a control can’t be programmatically disabled, as is the case with the view state. The control state is persisted at this time, too. Control state is another state storage mechanism whose contents are maintained across page postbacks much like the view state, but the purpose of the control state is to maintain necessary information for a control to function properly. That is, state behavior property data for a control should be kept in the control state, while user interface property data (such as the control’s contents) should be kept in the view state.

The SaveStateComplete event occurs when the state of controls on the page have been completely saved to the persistence medium.

Note

The view state of the page and all individual controls is accumulated in a unique memory structure and then persisted to storage medium. By default, the persistence medium is a hidden field named __VIEWSTATE. Serialization to, and deserialization from, the persistence medium is handled through a couple of overridable methods on the Page class: SavePageStateToPersistenceMedium and LoadPageStateFromPersistenceMedium. For example, by overriding these two methods you can persist the page state in a server-side database or in the session state, dramatically reducing the size of the page served to the user. Hold on, though. This option is not free of issues, and we’ll talk more about it in Chapter 19.

Generating the Markup

The generation of the markup for the browser is obtained by calling each constituent control to render its own markup, which will be accumulated in a buffer. Several overridable methods allow control developers to intervene in various steps during the markup generation—begin tag, body, and end tag. No user event is associated with the rendering phase.

The Unload Event

The rendering phase is followed by a recursive call that raises the Unload event for each control, and finally for the page itself. The Unload event exists to perform any final cleanup before the page object is released. Typical operations are closing files and database connections.

Note that the unload notification arrives when the page or the control is being unloaded but has not been disposed of yet. Overriding the Dispose method of the Page class—or more simply, handling the page’s Disposed event—provides the last possibility for the actual page to perform final clean up before it is released from memory. The page