In a recent post we provided a preview of the OpenInsight IMAGE API documentation for the upcoming release of version 10.1. As that proved quite popular we thought we’d provide some more, this time dealing with the Common GUI API (i.e. the basic interface that virtually every GUI object supports) and the WINDOW object API – two core areas of OI GUI programming.
Methods, not Events
One thing you may notice as you look through these documents is the addition of many new methods, such as SHOWOPTIONS or QBFCLOSESESSION – this is an attempt to tidy up the API into a more logical and coherent format that is a better fit for an object-based interface.
As we went through the product in order to document it, it became very apparent that there were many instances where events were being used to mimic methods, such as sending a WRITE event to save the data in a form, or sending a CLICK event to simulate a button click and so on. In object-based terminology this sort of operation would be performed by a method, which is a directive that performs an action – the event is a notification in response to that action. So, for example, you would call a “write” method to save your data and the system would raise a “write” event so you could deal with it.
Of course, this distinction will probably not bother many developers – just API purists like myself, but this does have another advantage if you like to use Object Notation Syntax (I do) – you can now perform actions such as reading and writing form data by using the”->” notation, whereas before you would have to use the Send_Event stored procedure which essentially breaks the object-based paradigm.
So instead of:
Call Send_Event( @Window, "WRITE" )
you would use the form’s WRITEROW method instead:
@@Window->WriteRow( "" )
which is a more natural fit for this style of programming.
(It is also easier to explain to new OI programmers who are used to other object-based languages and environments where everything is properties, methods and events).
Methods, not Stored Procedures
This brings us finally onto the topic of Stored Procedures and the object API, where several of these also fulfill the role of methods. For example, take the venerable Msg stored procedure used to display a message box for a parent form – a different way of treating this would be to have a SHOWMESSAGE method for the parent form rather than using a “raw” Msg call. Likewise for starting a new form: instead of using the raw Start_Window procedure, the SYSTEM and WINDOW objects now support a STARTFORM method instead.
Of course, none of this changes your existing code, nor is it enforced, it’s just something you can use if and when you wish to. However, even if my API pedantry hasn’t persuaded you to change your coding style, some of the new methods are worth investigating as they provide a better opportunity for us to extend the product’s functionality further – take a look at the WINDOW READROW and WRITEROW methods for an example of this – they support new features that we couldn’t do with just sending events.
In any case, here are the links – hopefully some light reading for your weekend!