Suppose you needed to enable and disable report regions on each page based on a parameter. You could add a condition to each region. If the conditions were all the same, the smart thing to do would be to create a function and have your condition reference the function.
What if your application had 100 pages? Would you remember to apply the condition to each report region in the 100 pages?
This is not a problem that most developers run into, however when you are building large applications something similar may come up. If you can find a way to dynamically control items, regions, processes, etc this can save on development time.
At the ODTUG Kaleidoscope conference Dennis Vanill gave a presentation on how to use Page 0 items to enable and disable APEX objects dynamically. Using this logic, here's an example on how to dynamically disable a region.
Note: Use this when appropriate. For basic conditions stick with using "regular" conditions
A demo is available here: http://apex.oracle.com/pls/otn/f?p=20195:1900
1- Create a page with some report regions
-- Interactive Report: SELECT * FROM emp -- Regular Report SELECT ename, sal FROM emp
2- Create Page Process: On Load - Before Header
DECLARE BEGIN IF NVL (:p1900_hide_reports_flag, 'N') = 'Y' THEN FOR x IN (SELECT region_id FROM apex_application_page_regions WHERE application_id = :app_id AND page_id = :app_page_id AND source_type IN ('Report', 'Interactive Report')) LOOP FOR i IN 1 .. apex_application.g_plug_id.COUNT LOOP IF apex_application.g_plug_id (i) = x.region_id THEN apex_application.g_plug_display_condition_type (i) := 'NEVER'; END IF; END LOOP; END LOOP; END IF; END;
2- (For Demo purposes only) I added the following on Page 0 to display in the example application. This shows that no conditions were applied to a region
SELECT region_id, region_name, source_type, condition_type, condition_expression1, condition_expression2, build_option, authorization_scheme FROM apex_application_page_regions WHERE application_id = :app_id AND page_id = :app_page_id
You can use the same logic to control computations, items, etc. Take a look at apex_application (desc apex_application) for more options.