Question about common practices on building applications on Tk (or "OO + Tk")
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From: Silas on 5 Mar 2010 14:32 Hello all, Some years ago I used Tcl 8.4 to create a relatively complex application. I didn't use many of the advanced techniques Tcl EIAS allowed, so I built it almost entirely pure imperative. Switched job and programming languages. After 3 years using C++ and Qt I switched back to Tcl to develop a small graphical tool. I realized that my mind was already settled on C++/Qt OO way so I tried to get OO on Tcl too. I have already studyied a bit of XOTcl, but since 8.6b1 is out now, I decided to give it a chance. TclOO works great and I can use most of the XOTcl features I used too (not the most advanced ones, but that is ok). The problem comes when I try to mix a well designed OO system with Tk. Tk widgets are always global and callbacks (the ones you bind with - command) also need to be global. I found some interesting references, but the doubt still persists. The references are: http://wiki.tcl.tk/21103 http://groups.google.com/group/comp.lang.tcl/browse_thread/thread/4defab229c59e325/f4eb65beb949ed1e?lnk=gst&q=oo+gui#f4eb65beb949ed1e My question is more general. Even before OO, I've never been satisfied that, after a well-built application, with correct function calling and encapsulation by scope, I had to deal with widgets declared globally. Since we can't just get rid or that feature, I'd like to ask: what are the practices you adopt when building your Tk applications? How would you layer your application in pure-Tcl core and Tk frontend? Thank you!
From: Arjen Markus on 8 Mar 2010 07:35
On 5 mrt, 20:32, Silas <sila...(a)gmail.com> wrote: > Hello all, > > Some years ago I used Tcl 8.4 to create a relatively complex > application. I didn't use many of the advanced techniques Tcl EIAS > allowed, so I built it almost entirely pure imperative. Switched job > and programming languages. After 3 years using C++ and Qt I switched > back to Tcl to develop a small graphical tool. > > I realized that my mind was already settled on C++/Qt OO way so I > tried to get OO on Tcl too. I have already studyied a bit of XOTcl, > but since 8.6b1 is out now, I decided to give it a chance. TclOO works > great and I can use most of the XOTcl features I used too (not the > most advanced ones, but that is ok). > > The problem comes when I try to mix a well designed OO system with Tk. > Tk widgets are always global and callbacks (the ones you bind with - > command) also need to be global. I found some interesting references, > but the doubt still persists. The references are: > > http://wiki.tcl.tk/21103http://groups.google.com/group/comp.lang.tcl/browse_thread/thread/4de... > > My question is more general. Even before OO, I've never been satisfied > that, after a well-built application, with correct function calling > and encapsulation by scope, I had to deal with widgets declared > globally. Since we can't just get rid or that feature, I'd like to > ask: what are the practices you adopt when building your Tk > applications? How would you layer your application in pure-Tcl core > and Tk frontend? > > Thank you! The Wiki has several pages on that very subject (model-view-controller is the technical term - http://wiki.tcl.tk/6225). But a down-to-earth approach could be: - Keep the set-up of your Tk widgets in dedicated procs - Use callback procedures to add the functionality you need, do not do: button .b -text Exit -command {puts $::outfile [array get myState]\; exit} but: button .b -text Exit -command SafeData - Use explicit namespaces and namespace variables in them to keep track of the state of your application (both the internal logic and the visual aspect) instead of just global variables. Regards, Arjen |