One of the areas in which dropdown comboboxes have always been lacking is the ability to fully control when the list is populated in a visually pleasing manner. Under most circumstances the contents are loaded well before the dropdown button is clicked, and this is fine, but in situations where the items are context -sensitive it is necessary to load them just before the list is shown, and in previous versions this can look a little messy.
You can see an example of this in the OI9 System Editor++: there is a very handy pair of dropdowns at the top if the form that allow you to navigate your source code using inserts and labels, but when you use them you see the list contents loaded just after it has been dropped; this looks somewhat jarring and usually causes issues with the vertical scrollbar too.
Of course, the reason for this is that OpenInsight events are normally fired in an asynchronous manner, and the DROPDOWN event won’t run until after the list has been shown. While you do have the ability to fire events in a synchronous fashion, this can introduce other complications and is something that should be avoided whenever possible.
So, in order to fix this, OpenInsight 10 provides a new property called AUTODROPDOWN that allows the list to be loaded during the DROPDOWN event and then displayed precisely when needed.
AUTODROPDOWN is a boolean property and is set to TRUE$ by default.
- When set to TRUE$ the combobox behaves in exactly the same way as previous versions.
- When set to FALSE$, the list is not shown until you explicitly set the DROPDOWN property to TRUE$. This gives you ability to load the list contents and then show them when ready.
Here’s an example of loading a list of STPROC repository items in a DROPDOWN event when AUTODROPDOWN is FALSE$
// Get a list of items reposIDs = get_Repos_Entities( "", "STPROC", "", FALSE$, | TRUE$, FALSE$, "" ) // Load them into the combobox LIST property call set_Property_Only( ctrlEntID, "LIST", reposIDs ) // Now show the list call set_Property_Only( ctrlEntID, "DROPDOWN", TRUE$ )
Comboboxes as options buttons?
Another area where AUTODROPDOWN may help is for systems that use comboboxes as a combined edit and options control, where clicking the dropdown button loads a dialog box or popup instead of dropping a list. Again, in previous versions this tends to look a little crude because the combobox shows a very shallow list even though it is empty, but with AUTODROPDOWN set to FALSE$ the list is never shown, and consequently looks much better.
(Disclaimer: This article is based on preliminary information and may be subject to change in the final release version of OpenInsight 10).