Standalone screen without process

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n/A

postedon September 23, 2013at 10:56 AM

I created a screen and I started it from the studio by clicking the Start Screen button. When I then hit a button in my screen, which has a Script Action attached, I get the following error:

Workspace Form not found

Is this a restriction of standalone screens or am I doing something wrong?

Stephan

repliedon September 23, 2013at 12:09 PM

Hi Biörn,

This is in fact a restriction of standalone screens. Appway does not keep a server-side state for such a screen. If the screen is referenced by a screen task in a process and rendered in the context of the execution of this process, the screen's scope and other context information is stored on the server side in the process instance its value store. But standalone screens are stateless.

That does not mean that they are useless. You can add an HTML Form component to such a screen and use other components like "HTML Text Field", "HTML Text Area" and "HTML Checkbox" to collect information from a user. The form's action URL could point to a script function which will take care of processing the request parameters and maybe redirect the user to an other screen afterward. You can even submit the form data to the screen itself. You only have to make sure that your screen has an assigned variable with the same name as the name of the HTML input components (HTTP parameter). If you call a standalone screen with a GET or POST request, Appway tries to assign the request parameter values to local variables of this screen.

Components and actions which require a server-side state however do not work in a standalone screen. This includes all components with a binding expression (also called "controls") like "Text Field", "Checkbox", "Dropdown List" etc. And it also includes actions which should get executed on the server side like "Script Action", "Process Action" and "URL Action".

- Stephan

Stephan

repliedon September 23, 2013at 12:15 PM

The biggest disadvantage of standalone screens is that they are stateless. And the biggest advantage is ... that they are stateless. If you have a couple of standalone screens and a user visits them one after the other, the user can create bookmarks for every screen and even use the browser's Back button. This is not possible with screens invoked during process execution, because the server-side state (the process instance) changes over time and is deleted as soon as the process ends. Bookmarks with ids of process tokens (= workitems) and process instances like in "/process/1323577364321" therefore do not work as bookmarks.

This is why we are currently rebuilding parts of our support and developer site. Pages which are used only to display simple information from a database will be implemented as standalone screens. Only a few actions (e.g. opening a new support ticket) will be implemented as processes.

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