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.\" ========================================================================
.\"
.IX Title "mega 3"
.TH mega 3 2023-07-25 "perl v5.38.0" "User Contributed Perl Documentation"
.\" For nroff, turn off justification.  Always turn off hyphenation; it makes
.\" way too many mistakes in technical documents.
.if n .ad l
.nh
.SH NAME
Tk::mega \- Perl/Tk support for writing widgets in pure Perl
.SH SYNOPSIS
.IX Header "SYNOPSIS"
Define the widget's new class name:
.PP
\ \ \ \ \fBpackage Tk::\fR\fIMyNewWidget\fR;
.PP
For composite widget classes:
.PP
\ \ \ \ \fBuse base qw/ Tk::container /\fR; # where \fBcontainer\fR is \fIFrame\fR or \fIToplevel\fR
.PP
For derived widget classes:
.PP
\ \ \ \ \fBuse base qw/ Tk::Derived Tk::DerivedWidget /;\fR
.PP
Install the new widget in Tk's namespace and establish class and instance
constructors.
.PP
\ \ \ \ \fBConstruct Tk::\fR\fIWidget\fR \fI'MyNewWidget'\fR;
.PP
\ \ \ \ \fBsub ClassInit\fR { \fImy ($self, \fR\f(CI$args\fR\fI) = \fR\f(CI@_\fR\fI; ...\fR }
.PP
\ \ \ \ \fBsub Populate\fR { \fImy ($self, \fR\f(CI$args\fR\fI) = \fR\f(CI@_\fR\fI; ...\fR }
.SH DESCRIPTION
.IX Header "DESCRIPTION"
The goal of the mega-widget support of Perl/Tk is to make it
easy to write mega-widgets that obey the same protocol and
interface that the Tk core widgets support.
\&\fIFor mega-widget sample code please run the \fR\f(BIwidget\fR\fI demonstration program and go to the section \fR\f(BISample Perl Mega-Widgets\fR\fI.\fR
.PP
There are two kinds of mega-widgets:
.IP \(bu 4
Composite Widgets
.Sp
A composite widget is composed with one or more existing widgets.
The composite widget looks to the user like a simple single widget.
A well known example is the file selection box.
.IP \(bu 4
Derived Widgets
.Sp
A derived widget adds/modifies/removes properties and methods
from a single widget (this widget may itself be a mega-widget).
.SH "MEGA-WIDGET SUPPORT"
.IX Header "MEGA-WIDGET SUPPORT"
.SS Advertise
.IX Subsection "Advertise"
Give a subwidget a symbolic name.
.PP
Usage:
.PP
\ \ \ \ \fR\f(CI$self\fR\fI\fR\->\fBAdvertise\fR(\fBname\fR=>\fI\fR\f(CI$widget\fR\fI\fR);
.PP
Gives a subwidget \fR\f(CI$widget\fR\fI\fR of the mega-widget \fI\fR\f(CI$self\fR\fI\fR the
name \fBname\fR.  One can retrieve the reference of an advertised subwidget
with the Subwidget method.
.PP
\&\fBComment:\fR Mega-Widget Writers: Please make sure to document the
advertised widgets that are intended for \fIpublic\fR use.
If there are none, document this fact, e.g.:
.PP
.Vb 1
\&        =head1 ADVERTISED WIDGETS
\&
\&        None.
.Ve
.SS Callback
.IX Subsection "Callback"
Invoke a callback specified with an option.
.PP
Usage:
.PP
\ \ \ \ \fR\f(CI$self\fR\fI\fR\->\fBCallback\fR(\fI\-option\fR ?,\fIargs\fR ...?);
.PP
\&\fBCallback\fR executes the callback defined with
\&\fR\f(CI$self\fR\fI\fR\->\fBConfigSpecs\fR(\fI\-option\fR, [\fBCALLBACK\fR, ...]);
If \fIargs\fR are given they are passed to the callback. If
\&\fI\-option\fR is not defined it does nothing.
.SS ClassInit
.IX Subsection "ClassInit"
Initialization of the mega-widget class.
.PP
Usage:
.PP
\ \ \ \ \fBsub ClassInit\fR { \fImy ($class, \fR\f(CI$mw\fR\fI) = \fR\f(CI@_\fR\fI;\fR ...  }
.PP
\&\fBClassInit\fR is called once for \fIeach\fR MainWindow
just before the first widget instance of a class is created in
the widget tree of \fBMainWindow\fR.
.PP
\&\fBClassInit\fR is often used to define bindings and/or other
resources shared by all instances, e.g., images.
.PP
Examples:
.PP
.Vb 3
\& $mw\->bind($class,"<Tab>", sub { my $w = shift; $w\->Insert("\et"); $w\->focus; $w\->break});
\& $mw\->bind($class,"<Return>", [\*(AqInsert\*(Aq,"\en"]);
\& $mw\->bind($class,"<Delete>",\*(AqDelete\*(Aq);
.Ve
.PP
Notice that \fR\f(CI$class\fR\fI\fR is the class name (e.g. \fBTk::MyText\fR) and \fI\fR\f(CI$mw\fR\fI\fR is the mainwindow.
.PP
Don't forget to call \fR\f(CI$class\fR\fI\fR\->\fBSUPER::ClassInit($mw)\fR in
\&\fBClassInit\fR.
.SS Component
.IX Subsection "Component"
Convenience function to create subwidgets.
.PP
Usage:
.PP
.Vb 4
\&    $cw\->Component(\*(AqWhatever\*(Aq, \*(AqAdvertisedName\*(Aq,
\&        \-delegate => [\*(Aqmethod1\*(Aq, \*(Aqmethod2\*(Aq, ...],
\&        ... more widget options ...,
\&    );
.Ve
.PP
\&\fBComponent\fR does several things for you with one call:
.Sp
.RS 4
o Creates the widget
.Sp
o Advertises it with a given name (overridden by 'Name' option)
.Sp
o Delegates a set of methods to this widget (optional)
.RE
.PP
Example:
.PP
.Vb 1
\&    $cw\->Component(\*(AqButton\*(Aq, \*(AqquitButton\*(Aq, \-command => sub{$mw\->\*(Aqdestroy\*(Aq});
.Ve
.SS ConfigSpecs
.IX Subsection "ConfigSpecs"
Defines options and their treatment
.PP
Usage:
.PP
.Vb 5
\&    $cw\->ConfigSpecs(
\&        \-option => [ where, dbname, dbclass, default],
\&        ...,
\&        DEFAULT => [where],
\&    );
.Ve
.PP
Defines the options of a mega-widget and what actions
are triggered by configure/cget of an option
(see Tk::ConfigSpecs and Tk::Derived for details).
.SS Construct
.IX Subsection "Construct"
Make the new mega-widget known to \fBTk\fR.
.PP
Usage:
.PP
\ \ \ \ \fBConstruct\fR \fIbaseclass\fR \fB'Name'\fR;
.PP
\&\fBConstruct\fR declares the new widget class so that your mega-widget
works like normal Perl/Tk widgets.
.PP
Examples:
.PP
\ \ \ \ \fBConstruct Tk::Widget\fR \fI'Whatever'\fR;
\ \ \ \ \fBConstruct Tk::Menu\fR   \fI'MyItem'\fR;
.PP
First example lets one use \fR\f(CI$widget\fR\fI\fR\->\fBWhatever\fR to create
new \fBWhatever\fR widget.
.PP
The second example restricts the usage of the \fBMyItem\fR constructor
method to widgets that are derived from \fBMenu\fR:
\&\fR\f(CI$isamenu\fR\fI\fR\->\fIMyItem\fR.
.SS CreateArgs
.IX Subsection "CreateArgs"
Process options before any widget is created:
.PP
\ \ \ \ \fBsub CreateArgs\fR { \fImy ($package, \fR\f(CI$parent\fR\fI, \fR\f(CI$args\fR\fI) = \fR\f(CI@_\fR\fI; ...; return \fR\f(CI@newargs\fR\fI;\fR }
.PP
\&\fR\f(CI$package\fR\fI\fR is the package of the mega-widget (e.g., \fBTk::MyText\fR,
\&\fI\fR\f(CI$parent\fR\fI\fR the parent of the widget to be created and \f(CW$args\fR the hash
reference to the options specified in the widget constructor call.
.PP
Don't forget to call \fR\f(CI$package\fR\fI\fR\->\fBSUPER::CreateArgs\fR(\fI\fR\f(CI$parent\fR\fI\fR, \fI\fR\f(CI$args\fR\fI\fR) in
\&\fBCreateArgs\fR.
.SS Delegates
.IX Subsection "Delegates"
Redirect a method of the mega-widget to a subwidget of
the composite widget
.PP
Usage:
.PP
.Vb 7
\&    $cw\->Delegates(
\&        \*(Aqmethod1\*(Aq => $subwidget1,
\&        \*(Aqmethod2\*(Aq => \*(Aqadvertived_name\*(Aq,
\&        ...,
\&        \*(AqConstruct\*(Aq => $subwidget2,
\&        \*(AqDEFAULT\*(Aq   => $subwidget3,
\&    );
.Ve
.PP
The \fB'Construct'\fR delegation has a special meaning.  After
\&'Construct' is delegated all Widget constructors are redirected.
E.g. after
.PP
\ \ \ \ \fR\f(CI$self\fR\fI\fR\->\fBDelegates\fR(\fB'Construct'\fR=>\fI\fR\f(CI$subframe\fR\fI\fR);
.PP
a \fR\f(CI$self\fR\fI\fR\->\fBButton\fR does really a \fI\fR\f(CI$subframe\fR\fI\fR\->\fBButton\fR
so the created button is a child of \fI\fR\f(CI$subframe\fR\fI\fR and not \fI\fR\f(CI$self\fR\fI\fR.
.PP
\&\fBComment:\fR Delegates works only with methods that \fR\f(CI$cw\fR\fI\fR does
not have itself.
.SS InitObject
.IX Subsection "InitObject"
\&\fINote: this method should not, in general, be used, as it has been
superceeded by \fR\f(BIPopulate\fR\fI and specifying \fR\f(BITk::Derived\fR\fI as one of the base
classes.\fR
.PP
Defines construction and interface of derived widgets.
.PP
Usage:
.PP
.Vb 4
\&    sub InitObject {
\&        my ($derived, $args) = @_;
\&        ...
\&    }
.Ve
.PP
where \fR\f(CI$derived\fR\fI\fR is the widget reference of the already created
baseclass widget and \fI\fR\f(CI$args\fR\fI\fR is the reference to a hash of
\&\fI\-option\-value\fR pairs.
.PP
\&\fBInitObject\fR is almost identical to Populate method.
\&\fBPopulate\fR does some more 'magic' things useful for mega-widgets
with several widgets.
.PP
Don't forget to call \fR\f(CI$derived\fR\fI\fR\->\fBSUPER::InitObject\fR(\fI\fR\f(CI$args\fR\fI\fR) in
\&\fBInitObject\fR.
.SS OnDestroy
.IX Subsection "OnDestroy"
Define a callback invoked when the mega-widget is destroyed.
.PP
Usage:
.PP
\ \ \ \ \fR\f(CI$widget\fR\fI\fR\->\fBOnDestroy\fR(\fIcallback\fR);
.PP
\&\fBOnDestroy\fR installs a callback that's called
when a widget is going to to be destroyed.  Useful
for special cleanup actions.  It differs from a normal \fBdestroy\fR
in that all the widget's data structures are still intact.
.PP
\&\fBComment:\fR This method could be used with any widgets not just
for mega-widgets.  It's listed here because of its usefulness.
.SS Populate
.IX Subsection "Populate"
Defines construction and interface of the composite
widget.
.PP
Usage:
.PP
.Vb 4
\&    sub Populate {
\&        my ($self, $args) = @_;
\&        ...
\&    }
.Ve
.PP
where \fR\f(CI$self\fR\fI\fR is the widget reference of the already created baseclass
widget and \fI\fR\f(CI$args\fR\fI\fR is the
reference to a hash of \fI\-option\-value\fR pairs.
.PP
Most the other support function are normally used inside the \fBPopulate\fR
subroutine.
.PP
Don't forget to call \fR\f(CI$cw\fR\fI\fR\->\fBSUPER::Populate\fR(\fI\fR\f(CI$args\fR\fI\fR) in
\&\fBPopulate\fR.
.SS privateData
.IX Subsection "privateData"
Set/get a private hash of a widget to storage
composite internal data
.PP
Usage:
.PP
\ \ \ \ \fR\f(CI$hashref\fR\fI\fR = \fI\fR\f(CI$self\fR\fI\fR\->\fBprivateData\fR();
.PP
\ \ \ \ \fR\f(CI$another\fR\fI\fR = \fI\fR\f(CI$self\fR\fI\fR\->\fBprivateData\fR(\fIunique_key\fR|\fIpackage\fR);
.SS Subwidget
.IX Subsection "Subwidget"
Get the widget reference of an advertised subwidget.
.PP
\ \ \ \ \fR\f(CI@subwidget\fR\fI\fR = \fI\fR\f(CI$cw\fR\fI\fR\->\fBSubwidget\fR();
.PP
\ \ \ \ \fR\f(CI$subwidget\fR\fI\fR = \fI\fR\f(CI$cw\fR\fI\fR\->\fBSubwidget\fR(\fIname\fR);
.PP
\ \ \ \ \fR\f(CI@subwidget\fR\fI\fR = \fI\fR\f(CI$cw\fR\fI\fR\->\fBSubwidget\fR(\fIname\fR ?,...?);
.PP
Returns the widget reference(s) of the subwidget known under the given
name(s). Without arguments, return all known subwidgets of \fR\f(CI$cw\fR\fI\fR. See
Advertise method how to define \fIname\fR for a subwidget.
.PP
\&\fBComment:\fR Mega-Widget Users: Use \fBSubwidget\fR to get \fIonly\fR
documented subwidgets.
.SH PITFALLS
.IX Header "PITFALLS"
.IP \(bu 4
Resource DB class name
.Sp
Some of the standard options use a resource date base class
that is not equal to the resource database name.  E.g.,
.Sp
.Vb 1
\&  Switch:            Name:             Class:
\&
\&  \-padx              padX              Pad
\&  \-activerelief      activeRelief      Relief
\&  \-activebackground  activeBackground  Foreground
\&  \-status            undef             undef
.Ve
.Sp
One should do the same when one defines one of these
options via \fBConfigSpecs\fR.
.IP \(bu 4
Method delegation
.Sp
Redirecting methods to a subwidget with \fBDelegate\fR
can only work if the base widget itself does have a
method with this name.  Therefore one can't ``\fIdelegate\fR''
any of the methods listed in Tk::Widget.
A common problematic method is \fBbind\fR.  In this case
one as to explicitely redirect the method.
.Sp
.Vb 5
\&  sub bind {
\&      my $self = shift;
\&      my $to = $self\->privateData\->{\*(Aqmy_bind_target\*(Aq};
\&      $to\->bind(@_);
\&  }
.Ve
.IP \(bu 4
privateData
.Sp
Graham Barr wrote: ... It is probably
more private than most people think. Not all calls to privateData will
return that same HASH reference. The HASH reference that is returned
depends on the package it was called from, a different HASH is returned
for each package. This allows a widget to hold private data, but then
if it is sub-classed the sub-class will get a different HASH and so not
cause duplicate name clashes.
.Sp
But privateData does take an optional argument if you want to
force which HASH is returned.
.IP \(bu 4
Scrolled and Composite
.Sp
\&\fBScrolled\fR(\fIKind\fR,...) constructor can not be used with \fBComposite\fR.
One has to use \f(CW$cw\fR\->\fBComposite\fR(\fBScrl\fR\fIKind\fR => \fB'name'\fR, ...);
.SH MISSING
.IX Header "MISSING"
Of course Perl/Tk does not define support function for
all necessities.  Here's a short list of things you have to
handle yourself:
.IP \(bu 4
No support to define construction-time only options.
.IP \(bu 4
No support to remove an option that is known to the
base widget.
.IP \(bu 4
It's hard to define \fBundef\fR as fallback for an widget
option that is not already \fBundef\fR.
.IP \(bu 4
Frame in Perl/Tk carries magic and overhead not needed
for composite widget class definition.
.IP \(bu 4
No support methods for bindings that are shared between all
widgets of a composite widget (makes sense at all?)
.SH KEYWORDS
.IX Header "KEYWORDS"
mega, composite, derived, widget
.SH "SEE ALSO"
.IX Header "SEE ALSO"
Tk::composite
Tk::ConfigSpecs
Tk::option
Tk::callbacks
Tk::bind