Object epiphany: A new way of building widget applications

[Martin Schultz <martin.schultz(at)dkrz.de>]

Hi all,

   With almost a week delay, I finally get around to release the first
version of a new class of IDL objects: the MGS_GUIObject hierarchy.
Don't shy away immediately! It's far easier than it sounds, and once
you will have discovered how easy it now becomes to develop widget
applications, you will get hooked! Ben Tupper has managed to get
something running within a day.

   Even though the package is only 68k (mostly documentation ;-), I
prefer not to attach it to this message but distribute it via
anonymous ftp (I may put it on my web site tomorrow). You can get
guiobjects_1-0.zip from
ftp://ftp.dkrz.de/pub/Outgoing/martin_schultz/idl/

   Before describing the object hierarchy a little, here is a quick
runup over the major features of this new approach:

(1) You can use the same object program to create blocking,
non-blocking, and compound widgets [makes testing of compound widgets
very easy and greatly increases re-usability of code]

(2) In general, you will not have to worry about widget event handling
in great depth. Most of this is taken care of for you in the basic
MGS_GUIObject already

(3) If you compose a widget out of several compound widgets, you
simply add them to a built-in container, and they will be managed
automatically for you. You only need to overwrite 3-4 methods (with
very simple code) to get very powerful widget programs.

(4) Due to the hierarchical class structure, it is very easy to
maintain the code. If you or I want to add a new basic feature to all
widget programs, the change only needs to be made once (in
MGS_GUIObject), and all programs will "see" the change immediately.

[Ben: what did I forget?]

Most of the programs described below contain an example procedure at
the end, so if you ".run mgs_...__define" and then call "example,
/block" you get to see what they do.


Hierarchy:

MGS_BaseObject : this is the father (or mother) of all my objects. It
contains a pretty sophisticated ErrorMessage interface including
traceback information and the choice to display errors as dialogs or
on the log window, and including a debug level. This object can also
clone itself and do a few other things.

MGS_Container : this object enhances the IDL_Container object by
allowing object access by name. Compared to the first version of about
a year ago, this version now also inherits from MGS_BaseObject to take
advantage of the error handling mechanism.

MGS_GUIObject : This is the "generic" widget object that lays the
foundation for all widget programs to come. It is fully functional in
itself, although all you will get is an empty frame with two buttons
("Accept" and "Cancel" or "Apply" and "Close" depending on the Block
keyword to the GUI method). The object already handles all major event
handling and the general procedure of building and displaying a widget
hierarchy. Inherited objects will only need to add the elemental or
compound widgets they need in a BuildGUI method; registration with the
XManager, positioning of the widget, etc. is all taken care of by
MGS_GUIObject. This object also allows you to set the default font and
the label font of your widgets (apparently not on a Mac: Pavel, please
test! - and only if you close and rebuild the GUI).

MGS_Field : This is a sibling of David's FSC_Field program but
extensively modified to make it fit into this new framework and to
make it even more modular. As a bonus, I added a character_mask
feature that allows you to specifiy the characters that shall be
allowed for string input. And, special offer for JD ;-) you can even
specify a regular expression which must then be matched by the input
field [needs some tuning, still]. Note, that you can use this field
object right away with four statements:
   thefield = Obj_New('MGS_Field', value=!DPI, min_valid=0.,
max_valid=10.,  $
                      labeltext='Enter value: ')
   thefield->GUI, /block
   print, 'Current field value is ',thefield->GetValue()
   Obj_Destroy, thefield

... and if you want to use it as a compound widget, see:

MGS_InputMask : This widget object simply collects information from a
structure and displays the structure tag values (must be scalars) in
individual MGS_Field input fields. Just think of how much work this
would be in classical widget programming, then take a look at this
code. You'll be amazed!!

MGS_RangeInput : This object demonstrates how to use two compound
widgets (again MGS_Field) and link them together to provide a range
input pair of fields. I admit they still need some more communication,
but you'll get the idea ...

MGS_Drawcolor : Again, you might recognize the name similarity to
David's FSC_Drawcolor program, and, indeed, that's what this does,
too: selecting a color.

MGS_GUIDemoObject : This object is yet another demonstration of how to
combine compound widgets. It builds a widget with three color picker
objects and one text field.



Now it's time for me to call the day,

hope you enjoy this new stuff,

Martin


PS: A great big thank you to David again for providing all this great
stuff on his web page - and for developing MPI_Plot which served as a
basis for the development of my programs.

-- 
[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[
[[ Dr. Martin Schultz   Max-Planck-Institut fuer Meteorologie    [[
[[                      Bundesstr. 55, 20146 Hamburg             [[
[[                      phone: +49 40 41173-308                  [[
[[                      fax:   +49 40 41173-298                  [[
[[ martin.schultz@dkrz.de                                        [[
[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[