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Re^3: Clearing anonymous Tk widgets

by Anonymous Monk
on Aug 31, 2012 at 10:51 UTC ( #990979=note: print w/ replies, xml ) Need Help??


in reply to Re^2: Clearing anonymous Tk widgets
in thread Clearing anonymous Tk widgets

Play with this

#!/usr/bin/perl -- use strict; use warnings; use Tk; use Tk::WidgetDump; use Tk::ObjScanner; my %ons; my $mw = tkinit(); for (1 .. 3) { my $goner = $_; $ons{$_} = $mw->Button( -text => "B $_", -command => sub { delete($ons{$goner})->destroy; ## this works, proper closu +re #~ delete($ons{$_})->destroy; ## this doesnt, $_ is alias } )->pack; } $mw->WidgetDump; ## before scan_object Tk::ObjScanner::scan_object( { mw => $mw, ons => \%ons } ); ## after W +idgetDump MainLoop();


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Re^4: Clearing anonymous Tk widgets
by murrayn (Acolyte) on Sep 01, 2012 at 03:53 UTC
    That looks promising. I'll have a play over the next few days (it's Father's Day in Aus tomorrow - there'd be trouble if I was messing with Perl code then!). I was starting to think I'd need an array of Tk Frames and go destroying them but this looks more elegant. Thanks. I'll let you know how it goes.
      So this is my rewrite of the above using a hash to track each entry which I may want to delete...
      for (keys %runtime) { $widgetname = $_; $widgetrow{$widgetname} = $workframe -> Frame(); $wrLabel{$widgetname} = $widgetrow{$widgetname} -> Label(-text=>$w +idgetname) -> grid(-row=>1, -column=>1); $wrEntry{$widgetname} = $widgetrow{$widgetname} -> Entry(-width=>1 +00, -textvariable=>\$runtime{$widgetname}) -> grid(-row=>1, -column=> +2); $wrButton{$widgetname} = $widgetrow{$widgetname} -> Button(-text=> +"Delete \"$widgetname\" entry", -command=>sub { my $deltgt = $widgetname; print "Deleting \"$deltgt->$runtime{$deltgt}\"\n"; delete $runtime{$deltgt}; print "Hash entry deleted\n"; delete($wrLabel{$deltgt})->destroy(); print "Widget label deleted and destroyed\n"; delete($wrEntry{$deltgt})->destroy(); print "Widget entry deleted and destroyed\n"; delete($wrButton{$deltgt})->destroy(); print "Widget button deleted and destroyed\n"; $widgetrow{$deltgt} -> destroy(); print "Widget row destroyed\n"; } ) -> grid(-row=>1, -column=>3); $widgetrow{$widgetname} -> grid(-row=>$row, -column=>1, -columnspa +n=>3); $rowsin = $row; $row++; }
      This produces a Tk frame for each variable and puts three objects in that frame: 1) the variable name, as a Tk Label, which is the key to the %runtime hash, 2) the value from the %runtime hash as a Tk Entry field and 3) a Tk Button with text saying "Delete "Variable" Entry".

      After that frame is built, it's inserted in $workframe on the next available line.

      This all works nicely and the buttons all have their correct variable names written on them.

      However, when I press the button, ANY button, the value of $widgetname is the last key accessed from the %runtime hash and that's the entry which is deleted from the hash and the subframe which is deleted from the workframe. A subsequent attempt to use any button generates an Tk error stating that I cannot delete an undefined object.

      (I put the "my $deltgt=$widgetname" line in hoping that I might sufficiently localise the variable at "build" time that I could retain it ready for execution time - didn't work, not surprised.)

      Perhaps I need a mechanism to read the text from the button which invoked the subroutine. The button is generated and remains static as the loop rolls on so the target variable name can be stored therein if only I could extract that.

        Solved! The key is in the -command and passing parameters to a callback on a widget. The code above doesn't work because "$widgetname" is being evaluated at the time the button is released by which time the value has changed from what was intended. The challenge is to tell the callback associated with the button what the value was at the time the button was created and that is done by passing it as an argument to the callback thus:
        -command=> [sub { my $deltgt = shift; print "Deleting \"$deltgt->$runtime{$deltgt}\"\n"; delete $runtime{$deltgt}; print "Hash entry deleted\n"; delete($wrLabel{$deltgt})->destroy(); print "Widget label deleted and destroyed\n"; delete($wrEntry{$deltgt})->destroy(); print "Widget entry deleted and destroyed\n"; delete($wrButton{$deltgt})->destroy(); print "Widget button deleted and destroyed\n"; $widgetrow{$deltgt} -> destroy(); print "Widget row destroyed\n"; }, $widgetname]

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