[Kde-perl] Why isn't this easy? implementing File->New

[darrik]

Ashley Winters wrote:
> --- darrik <darrik at mythofbutterfly.com> wrote:
> 
>> Ashley Winters wrote:
>>> use strict;
>>> use Qt;     # use Qt in EVERY package! It declares 'this', and does
>>> other use-strict-happy things
>>> use MyView;
>>> sub processFileMenu {
>>> 	if ($option==FILENEW) {
>>> 		MyView(this)->show;
>>> 	}
>>> }
>> You're not storing a perl reference to the new window anywhere.  What
>>
>> happens when you want to access that window from the parent later?
> 
> Ahh, in that case you want to store it as a member variable. If, for
> example, we wanted to populate the Window menu with the list of windows
> opened with File->New or something...
> 
> package YourClass;
> use strict;
> use Qt;
> use Qt::isa qw(Qt::Widget);
> use Qt::attributes qw(windows);    # declare a member variable
> use MyView;
> 
> sub NEW {
>     # standard preamble
> 
>     windows = [];    # initialize as an array
> }
> 
> sub processFileMenu {
> 	if ($option==FILENEW) {
> 		my $viewer = MyView(this);
> 		$viewer->show;
> 		push @{ windows }, $viewer;
> 	}
> }
> 
>> This is more evident when you subclass a container widget that has
>> child 
>> controls.  For instance:
> 
> I'll make the edits inline...
> 
>> use strict;
>>
>> package MyWidget;
>>
>> use Qt;
>> use Qt::isa qw( Qt::Widget );
> 
> use Qt::attributes qw( lbl );
> 
>> sub NEW {
>>    # irrelevant method arguments left out for brevity :P
>>
>>    my $class=shift;
>>    my $parent=shift;
>>    shift->SUPER::NEW($parent);
>>    my $layout=Qt::HBoxLayout(this);
> #>    my $lbl=Qt::Label("label",this);
> #>    $layout->addWidget($lbl);
> 
>     # instead
>     lbl = Qt::Label("label",this);
>     $layout->addWidget(lbl);
>> }
>>
>> sub changeChildLabel {
>>    # how do you access $lbl here?
>     lbl->setText("Qt::attributes");
>> }
> 
> 
>> This part has me confused.  Storing $lbl in a package variable
>> doesn't 
>> work if you instantiate several MyWidget's.  I've been using
>> workarounds 
>> that are inelegant, so a pointer to the *proper* way to do this would
>> be 
>> immensely appreciated.
> 
> Sure. Keep in mind that the 'this' function/variable/keyword thing is,
> in fact, a hash. You're free to store things in it, like so:
> 
> this->{'lbl'} = Qt::Label(...);
> 
> In fact, that's all the Qt::attributes pragma does, is setup that
> shortcut. It automatically creates a lbl() function which returns
> this->{'lbl'}, in a way that lets you assign to it (as an lvalue).
> 
> That's the technical side, at least. For more of a tutorial, read this:
> 
> http://perlqt.sourceforge.net/dist/current/doc/en/index.html#using_attributes
> 
> - Ashley Winters

Superb!  And well-explained!  Thank you kindly!

I was thinking about this()->{lbl} but wasn't sure if that would work. 
The Qt::attributes solution is much cleaner and clearer.

Again, thanks a lot! :)

Darrik Mazey