Computation points - need to understand when they trigger

Question

Hi,
Can anyone please assist me in understanding computation points...
I've used (Before Header - on the first instance of the page) in the application... need to understand the others (such as After Header, Before Regions, After Regions, etc...) as when they trigger and some examples of application...
Thanks in advance

Answer 1

Hello,
>> …need to understand the others (such as After Header, Before Regions, After Regions, etc...) as when they trigger ….
Although the Computations you are talking about are part of the Page Rendering phase, it’s important to remember that they are actually triggered by the server – the APEX Engine – as part of generating the application page code. It means that these Computations are not triggered when the page actually runs on the client.
The Firing points are shared by both Computation and Processes, but are more relevant to the latter. They actually reference the different stages in generating the page code (and not necessarily the sequence of running it).
Computations allow you to set the value of page/application items. All of these are available to the APEX Engine prior to starting the rendering process, so in APEX terms they are already available in the Before Header stage, and for all the following stages. However, right now I can’t think of an example that force you to set a Computation firing point other than Before Header (as we are talking about the rendering phase, After Submit is excluded).
With Processes things might look differently, especially if we are using them to generate some dynamic code that depends on the values/existing of items or DOM elements. For example, if we want to add some JavaScript code that will close a (popup) window prior to its rendering, we should fire it before header. However, if we want to include a script that manipulates the region header title, it should be included before the APEX Engine code for that region, so we should choose a firing point of Before Region. Relying on the same logic, if we need to generate a script that uses DOM elements that are only created with the region, we must append it after the code for the regions, so we should choose the After Region (or later) firing point.
I hope this makes things a bit clearer for you.
Regards,
Arie.
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