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List: kde-perl
Subject: Re: [Kde-perl] Why isn't this easy? implementing File->New
From: darrik <darrik () mythofbutterfly ! com>
Date: 2006-08-02 6:25:00
Message-ID: 44D0453C.9070602 () mythofbutterfly ! com
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Ashley Winters wrote:
> --- darrik <darrik@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
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