Re: Fwd: (fwd) binding to a derived canvas widget

Steve Lidie <[email protected]> writes:
>Here's how to do it (in Populate):
>
>    $self->{'real_can'} = $self->{'can'}->Subwidget('scrolled');  
>######## more on this later
>    my( @bindtags ) = $self->{'real_can'}->bindtags;
>    $self->{'real_can'}->bindtags( [ @bindtags, 'CanvasDirTree-B1' ] );
>    $self->{'real_can'}->CanvasBind( 'CanvasDirTree-B1', '<Button-1>'  
>=> [\&pick_one, $self] );

All that is fine. But bindtags includes the name of the class already.
This is so that one can assoicate class bindings with it.

So what I intended for one to do was:

   $self->{'real_can'}->CanvasBind( ref($self), '<Button-1>'  ...);

But that is I hope unnecessarily complicated - see below.

>>
>> sub ClassInit
>> {
>>     my ($class, $mw) = @_;
>>     $class->SUPER::ClassInit($mw);

    What that will do by the way is call Canvas::ClassInit.
    This isn't quite a no-op - it calls XYscrollBind
    Which binds mouse wheel and <Up>, <Down> etc. so that 
    scrolls happen (if widget has the focus for keystroke cases).

    Once that has happened - and of course if you don't want 
    that you don't have to call it! 
    We can now add bindings to the class name.
    Which would look like:

    $mw->bind( $class, '<Button-1>', 'pick_one' );
>> }

At this point $mw is _a_ widget (the MainWindow) which is all we need
to talk to core Tk. It isn't a Canvas so no spurious binds are in scope.
And it is called as a "static" method so 1st arg is the class name.
As 'pick_one' is a sub in our class we treat it as a method just use its 
name in the binding.

When a particular _instance_ of the class gets a Button-1 the class binding
is called and the sub is called (as a method) passing the instance 
widget as 1st arg. This achieves the same as original 

     ... '<Button-1>' => [\&pick_one, $self] );

But with the additional advantage that if someone derives from _your_ 
class they can override the pick_one method if your pick_one isn't 
quite what they want.






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