Editing API:EPrints/Plugin/Screen (section)

==DESCRIPTION==
Screen plugins provide the CGI user interface to EPrints. Only "static" pages (summary pages, browse views) are not rendered via screens.

Screens generate elements of the page that are then rendered using the [[API:EPrints/Apache/Template|EPrints::Apache::Template]]. These elements include the page title, header elements and page body. Screens can also '''export''' (depending on [[API:EPrints/Plugin/Screen#wishes_to_export|wishes_to_export]]) which allows complete control over the HTTP response.

Most screens have an interactive element that follow this pattern:

first request ...

* 1. can_be_viewed() grants access
* 2. properties_from() sets up the response
* 3. render() includes a form with an action
second request ...

* 4. properties_from() sets up the response
* 5. from() identifies the action
* 6. allow_*() checks access to the specific action
* 7. action_*() method performs the (probably) side-effecting action
* 8. redirect_to_me_url() redirects the user back to ...
third request ... back to step 1.

The exception to this is where [[API:EPrints/Plugin/Screen#redirect_to_me_url|redirect_to_me_url]] is sub-classed to return undef, in which case the screen is expected to render in addition to processing the form request.

The reason for using a redirect is that the user will end up on a page that can be reloaded without re-submitting the form. This is particularly important where submitting the action twice may result in an error, for example when deleting an object (can't delete twice!). 

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