[clue-tech] First example Ruby Gtk program

[dennisjperkins at comcast.net]

 -------------- Original message ----------------------
From: Match Grun <match at dim.com>
> On Thu, 25 Oct 2007 22:16:33 -0600
> Dennis J Perkins <dennisjperkins at comcast.net> wrote:
> 
> > #! /usr/bin/env ruby
> > 
> > # Display the canonical "hello world" message of a first
> > # program in a new programming language.
> > 
> > # Note that this program has a flaw that manifests itself 
> > # when shutting down.  Clicking on the close button makes
> > # the window disappear, but the event loop is still running.
> > # This solution to this issue will be shown in another example
> > # program.
> > 
> > # Use Ruby's gtk2 library.
> > require "gtk2"
> > 
> > # Initialize Gtk.
> > Gtk.init
> > 
> > # Create the toplevel window,
> > win = Gtk::Window.new
> > 
> > # Add a title to the program.
> > win.set_title "Hello World"
> > 
> > # Add a 10-pixel border to the edge of the toplevel window canvas.
> > win.border_width = 10
> > 
> > # Create a label to display our "Hello world" message.
> > label = Gtk::Label.new "Hello world"
> > 
> > # Add our newly created label to the toplevel window.
> > win.add label
> > 
> > # Widgets are not automatically visible, so make them visible now.
> > # The toplevel window should be made visible last to avoid seeing 
> > # widgets and the toplevel window change size as the packing manager
> > # change size as the packing manager figures out the appropriate sizes
> > # for everything.
> > 
> > label.show
> > win.show
> > 
> > # Start the event loop.
> > Gtk.main
> > 
> > _______________________________________________
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> 
> 
> Dennis,
> 
> This is not a "flaw". The same problem exists with several programming
> languages and platforms.
> 
> With GUI programming, it is up to the programmer to hook up the desired
> action to every event that is important in a GUI. Clicking the close
> button should invoke the necessary steps to close the window
> component of the GUI and possibly the event loop, if that is the
> desired action.
> 
> It should never be assumed that closing a window should automatically
> stop the main event loop. After all, it is possible that there are
> several open windows in an application. Closing any one of them does
> not automatically assume that the application should terminate.
> 
> In GUI programming, it is usual to provide some command menu function
> (eg, quit) that closes all open windows and terminates the process.
> Perhaps, the function also checks whether the work has been saved and
> prompts the user accordingly. In this case the window should not be
> closed. If the application has a main window, the close button would
> typically execute the same function as the command menu quit function.
> 
> Hope that helps.
> 
> Match
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You're right.  And I already knew why it does that, altho I didn't consider multiple open windows.  I should have worded that differently.  

Apparently more people are reading this list than I thought.  We started on Ruby Gtk last week, and I intended these for the others in the study group.  I hope they are helpful to others.