• Programming PerlQt
• Introduction
• Installation
• Requirements
• Compilation
• Troubleshooting and Configure Options
• How to install PerlQt with user rights
• Anatomy of PerlQt
• Hello World
• Inheritance and Objects
• A Custom Widget
• Using Attributes
• Signals and Slots
• RAD prototyping with Qt Designer and Puic
• Introduction
• Embedding Images
• Working With .ui Files
• More development tools
• pqtapi
• pqtsh
• Known Limitations
• Credits
• Appendix 1 : C++ conventions and their Perl counterpart
• Appendix 2 : Internationalization
• disabling utf-8
• Appendix 3 : Debugging Channels
• Appendix 4 : Marshallers

Programming PerlQt

Germain Garand

This document describes a set of Perl bindings for the Qt toolkit. Contact the author at <germain@ebooksfrance.com>

Introduction

PerlQt-3 is Ashley Winters' full featured object oriented interface to Trolltech's C++ Qt toolkit v3.0.

It is based on the SMOKE library, a language independent low-level wrapper generated from Qt headers by Richard Dale's kalyptus thanks to David Faure's module.

This document describes the principles of PerlQt programming. It assumes you have some basic Perl Object Oriented programming knowledge.

Some C++ knowledge is recommended but not required. It would mostly help you to find your way through Qt's excellent documentation which is our ultimate and only reference. If Qt is installed on your system, then you most probably also have its documentation. Try the $QTDIR/bin/assistant program.

Installation

Requirements

To compile and use PerlQt, you'll need :

a POSIX system
GNU tools : automake(>=1.5), autoconf (>=2.13), aclocal...
Perl >= v5.6.0
Qt >= v3.0
SmokeQt 1.2.1 The SMOKE library (Scripting Meta Object Kompiler) is part of KDE's kdebindings module. You may want to check if a precompiled version of this module exists for your system. PerlQt is packaged with its own copy, so you don't need to check it out.

Perl and Qt's installation is out of the scope of this document. Please refer to those projects' documentation.

Compilation

PerlQt uses GNU's Autoconf framework. However, the standard ./configure script is preferably driven by the Makefile.PL wrapper. All options are forwarded to ./configure :

 perl Makefile.PL

If SMOKE is missing, configure will generate its sources. Then :

 make

 make install

This will install PerlQt, Puic and Smoke (if needed), as well as the pqtsh and pqtapi utilities.

The preferred install location for SMOKE and Puic is in the KDE3 file system. If you don't have KDE3 installed, specify a location with configure's --prefix option. e.g:

 perl Makefile.PL --prefix=/usr

Troubleshooting and Configure Options

If Smoke's linking fails or your Qt library was built with very specific options, run Makefile.PL again with:

 perl Makefile.PL --with-threshold=0

When building smoke, configure will check for OpenGL and try to compile support for it if it is properly installed and supported by Qt.

You may disable this checking with:

 --disable-GL

Also, default behaviour is to prefer the Mesa GL library over a proprietary implementation. If your system features a proprietary OpenGL library, and you'd like to use it, specify:

 --without-Mesa

How to install PerlQt with user rights

To install PerlQt without super-user rights, simply follow this procedure:

Perform a normal configuration, specifying as prefix a directory where you have write permissions :

 perl Makefile.PL --prefix=~

The above would install the Smoke library in ~/lib and the puic binary in ~/bin

Reconfigure the Perl module so that it doesn't target the standard perl hierarchy:

 cd PerlQt
 perl Makefile.PL PREFIX=~
 cd ..

Beware : this is not the same Makefile.PL as above, but the one located in the ./PerlQt subdirectory

Compile and Install

 make && make install

In order to use such an installation, you must tell to Perl where to find this extern hierarchy. This can be done either on the command line:

 perl -Mlib="~/local/lib/perl/5.x.x" program.pl

or at the top of your program:

 use lib qw( ~/local/lib/perl/5.x.x );

``5.x.x'' should be changed to whatever Perl version your system is running.

Anatomy of PerlQt

A typical Qt program using GUI components is based on an event loop.

This basically means that such a program is no more envisioned as a straight flow where you would need to handle yourself every single events (such as a mouse click or a key press).

Instead, you just create an Application object, create the GUI components it uses, define what objects methods need to be called when an event occurs, and then start the main event loop.

That's all! Qt will handle all events and dispatch them to the correct subroutine.

Lets see how this process is implemented in a minimal PerlQt program.

Hello World

 1: use Qt;
 2: my $a = Qt::Application(\@ARGV);
 3: my $hello = Qt::PushButton("Hello World!", undef);
 4: $hello->resize(160, 25);
 5: $a->setMainWidget($hello);
 6: $hello->show;
 7: exit $a->exec;

This program first loads the Qt interface [line 1] and creates the application object, passing it a reference to the command line arguments array @ARGV [l.2]. This application object is unique, and may later be accessed from anywhere through the Qt::app() pointer.

At line 3, we create a PushButton, which has no parent (i.e : it won't be contained nor owned by another widget). Therefore, we pass to the constructor an undef value for the parent argument, which is PerlQt's way of passing a Null pointer.

After some layouting at [l.4], we tell the application object that our main widget is this PushButton [l.5]... that way, it will know that closing the window associated with this widget means : quit the application.

Now the last steps are to make this widget visible (as opposed to hidden, which is the default) by calling the show method on it [l.6] and to start the application loop [l.7].

Syntax elements summary :

All Qt classes are accessed through the prefix Qt::, which replaces the initial Q of Qt classes. When browsing the Qt documentation, you simply need to change the name of classes so that QFoo reads Qt::Foo.
An object is created by calling the constructor of the class. It has the same name as the class itself.

You don't need to say new Qt::Foo or Qt::Foo->new() as most Perl programmers would have expected.

Instead, you just say :

 my $object = Qt::<classname>(arg_1, ..., arg_n);

If you don't need to pass any argument to the constructor, simply say :

 my $object = Qt::<classname>;

Whenever you need to pass a Null pointer as an argument, use Perl's undef keyword. Do not pass zero. Beware: this is by far the most common error in PerlQt programs.

Pointers are arguments preceded by an * character in Qt's documentation (e.g: ``QWidget * widget'').

Inheritance and Objects

Before we can discuss how Perl subroutines can be called back from Qt, we need to introduce PerlQt's inheritance mechanism.

PerlQt was designed to couple as tightly as possible Qt's simplicity and Perl's power and flexibility.

In order to achieve that goal, the classical Object Oriented Perl paradigm had to be extended, much in the same way than Qt itself had to extend C++'s paradigm with metaobjects.

A Custom Widget

Lets rewrite the ``Hello World!'' program, this time using a custom version of PushButton:

  1: use strict;
  2: 
  3: package Button;
  4: use Qt;
  5: use Qt::isa qw(Qt::PushButton);
  6: 
  7: sub NEW
  8: {
  9:   shift->SUPER::NEW(@_[0..2]);
 10:   resize(130, 40);
 11: }
 12: 
 13: 1;
 14: 
 15: package main;
 16: 
 17: use Qt;
 18: use Button;
 19: 
 20: my $a = Qt::Application(\@ARGV);
 21: my $w = Button("Hello World!", undef);
 22: $a->setMainWidget($w);
 23: $w->show;
 24: exit $a->exec;

Here, we want to create our own version of the PushButton widget. Therefore, we create a new package for it [l.3] and import Qt [l.4].

We now want to declare our widget as subclassing PushButton. This is done through the use of the Qt::isa pragma [l.5], which accepts a list of one or more parent Qt classes.

It is now time to create a constructor for our new widget. This is done by creating a subroutine called NEW (note the capitalized form, which differentate it from the usual ``new'' constructor. PerlQt's NEW constructor is called implicitly as can be seen on line 21).

Since we want our widget to call its parent's constructor first, we call the superclass's constructor (here: Qt::PushButton) on line 9, passing it all arguments we received.

At this time, a class instance has been created and stored into a special object holder named this (not $this but really just this).

Each time you invoke a method from within your package, you may now indifferently say method() or this->method();

Using Attributes

When building a new composite widget, you may just create its different parts inside my variables, since widgets are only deleted by their parents and not necessarily when their container goes out of scope.

In other words, PerlQt performs clever reference counting to prevent indesirable deletion of objects.

Now, you'll often want to keep an access to those parts from anywhere inside your package. For this purpose, you may use the this object's blessed hash, as is usual in Perl, but that isn't really convenient and you don't have any compile time checking...

Here come Attributes. Attributes are data holders where you can store any kind of properties for your object.

Declaring new attributes is done through the use Qt::attributes pragma, as is demonstrated in the following package implementation :

  1: use strict;
  2:
  3: package Button;
  4: use Qt;
  5: use Qt::isa qw(Qt::PushButton);
  6: use Qt::attributes qw(
  7:     itsTime
  8:     pData
  9: );
 10:
 11: sub NEW
 12: {
 13:   shift->SUPER::NEW(@_[0..2]);
 14:   itsTime = Qt::Time;
 15:   itsTime->start;   
 16:   pData = " Foo ";
 17: }
 18: 
 19: sub resizeEvent
 20: {
 21:    setText( "w: ". width() ." h: ". height() .
 22:             "\nt: ". itsTime->elapsed . pData );
 23: }
 24:
 25: 1;

An attribute itsTime is declared at line 7, and loaded with a Qt::Time object at line 14.

Since we reimplement the virtual function ``resizeEvent'' [l.19]. each time the main widget is resized, this function will be triggered and our Button's text updated with values coming from the object [l.21] and from the attributes we defined [l.22].

Recapitulation

In order to inherit a Qt class, a package must contain a use Qt::isa pragma. e.g:

 use Qt::isa "Qt::widget";

The object constructor is named NEW and is implicitly called. Thus you should not say :

 my $o = MyButton->NEW("Hello");

But say :

 my $o = MyButton("Hello");

Within a package, the current instance can be accessed through the this variable.

When a member function is called, arguments are loaded as usual in the @_ array, but without the object pointer itself.

Hence, you shouldn't say :

 sub myMember
 {
   my $self = shift;
   my $arg = shift;
   $arg->doThat($self); 
   $self->doIt;
 }
    
But :

 sub myMember
 {
   my $arg = shift;
   $arg->doThat(this);
   doIt;
 }

Furthermore, if you want to call a base class method from a derived class, you'd use the specal attribute SUPER :

 sub example
 {
   print "Now calling the base class\n";
   SUPER->example(@_)
 }

Note that the :

 this->SUPER::Example(@_);

construct is also available, but will pass the object as first argument.

Whenever you need to store a contained object in your package, you may define it as an Attribute :

 use Qt::attributes qw(
        firstAttribute
        ...
        lastAttribute);

and then use it as a convenient accessor :

 firstAttribute = myContainedWidget( this );
 firstAttribute->resize( 100, 100 );

To reimplement a virtual function, simply create a sub with the same name in your object.

Existing virtual functions are marked as such in Qt's documentation (they are prefixed with the ``virtual'' keyword).

You can inspect what virtual function names are being called by Qt at runtime by putting a use Qt::debug qw( virtual ) statement at the top of your program.

Signals and Slots

We'll now learn how Qt objects can communicate with each other, allowing an event occuring, for instance, in a given widget to trigger the execution of one or several subroutines anywhere inside your program.

Most other toolkits use callbacks for that purpose, but Qt has a much more powerful and flexible mechanism called Signals and Slots.

Signals and slots are used for communication between objects.

This can be thought off as something similar to the wiring between several Hi-fI components : an amplificator, for instance, has a set of output signals, wich are emitted wether a listening device is connected to them or not. Also, a tape recorder deck can start to record when it receives a signal wired to it's input slot, and it doesn't need to know that this signal is also received by a CD recorder device, or listened through headphones.

A Qt component behaves just like that. It has several output Signals and several input Slots - and each signal can be connected to an unlimited number of listening slots of the same type, wether they are inside or outside the component.

The general syntax of this connection process is either :

Qt::Object::connect( sender, SIGNAL 'mysignal(arg_type)', receiver, SLOT 'myslot(arg_type)');

or

myObject->connect( sender, SIGNAL 'mysignal(arg_type)', SLOT 'myslot(arg_type)');

This mechanism can be extended at will by the declaration of custom Signals and Slots, through the use Qt::signals and use Qt::slots pragma (see also the other syntax, later on).

Each declared slot will call the corresponding subroutine in your object, each declared signal can be raised through the emit keyword.

As an example, lets rewrite again our Button package :

  1: use strict;
  2:
  3: package Button;
  4: use Qt;
  5: use Qt::isa qw(Qt::PushButton);
  6: use Qt::attributes qw(itsTime);
  7: use Qt::slots 
  8:     wasClicked => [],
  9:     change     => ['int', 'int'];
 10: use Qt::signals
 11:     changeIt   => ['int', 'int'];
 12:
 13: sub NEW
 14: {
 15:   shift->SUPER::NEW(@_[0..2]);
 16:   itsTime = Qt::Time;
 17:   itsTime->start;   
 18:   this->connect(this, SIGNAL 'clicked()', SLOT 'wasClicked()');
 19:   this->connect(this, SIGNAL 'changeIt(int,int)', SLOT 'change(int,int)');
 20: }
 21: 
 22: sub wasClicked
 23: {
 24:    my $w = width();
 25:    my $h = height();
 26:    setText( "w: $w h: $h\nt: ". itsTime->elapsed );
 27:    emit changeIt($w, $h);          
 28: }
 29:
 30: sub change
 31: {
 32:    my ($w, $h) = @_;
 33:    print STDERR "w: $w h: $h \n";
 34: }
 35:
 36: 1;

In this package, we define two extra slots and one extra signal.

We know from the Qt Documentation that a clicked PushButton emits a clicked() signal, so we connect it to our new slot at line 18.

We also connect our signal changeIt to our own change slot- which is quite stupid, but as an example.

Now, whenever our Button is clicked, the clicked() signal is raised and triggers the wasClicked() slot. wasClicked then proceeds to emit the changeIt(int,int) signal [l.27], hence triggering the change(int,int) slot with two arguments.

Finally, since PerlQt-3.008, an alternative syntax can be used to declare Signals and Slots:

 sub a_slot : SLOT(int, QString)
 { 
        $int = shift;
        $string = shift;
        # do something
 }

and

 sub a_signal : SIGNAL(QString);

This syntax is perfectly compatible with the traditional use Qt::signals and use Qt::slots declarations.

Eventually, it can prove good programming practice to mix both syntaxes, by first declaring Signals/Slots with use Qt::slots/signals, then repeat this declaration in the actual implementation with the second syntax.

Declarations will be checked for consistency at compile time, and any mismatch in arguments would trigger a warning.

RAD prototyping with Qt Designer and Puic

Introduction

• Note:
  
As of PerlQt-3.008, a separate PerlQt plugin for Qt Designer is available, bringing full integration, syntax highlighting, code completion and allowing to run/debug your PerlQt project entirely from the Designer GUI. Nevertheless, the below is still accurate with regard to puic command line interaction and with regard to using Qt Designer without the specific plugin.

As efficient and intuitive as Qt can be, building a complete GUI from scratch is often a tedious task.

Hopefully, Qt comes with a very sophisticated GUI Builder named Qt Designer, which is close to a complete integrated development environment. It features Project management, drag'n drop GUI building, a complete object browser, graphical interconnection of signals and slots, and much much more.

Qt Designer's output is XML which can be parsed by several command line tools, among whose is puic (the PerlQt User Interface Compiler).

Assuming you have already built an interface file with the Designer, translating it to a PerlQt program is simply a matter of issuing one command :

 puic -x -o program.pl program.ui

This will generate the package defined in your ui file and a basic main package for testing purposes.

You may prefer :

 puic -o package.pm program.ui

This will only generate the package, which can then be used by a separate program.

Embedding Images

If you need to embed images or icons, it can be done in two ways :

• Inline embedding
  
For this, you need to check the ``Edit->Form Settings->Pixmaps->Save inline'' checkbox inside Qt Designer. Then : puic -x -o program.pl program.ui
• Image Collection
  
This option is more complex but also far more powerful and clean.

puic -o Collection.pm -embed unique_identifier image-1 ... image-n

Then add a use Collection.pm statement to your program's main package.

If you've created a project file in Qt Designer, and added all images you want to group (through ``Project->Image Collection''), you'll find all those images inside the directory where your project file (*.pro) is stored, under /images. You can then generate the corresponding image collection by issuing :

puic -o Collection.pm -embed identifier ../images/*

You can use as many image collections as you want in a program. Simply add a use statement for each collection.

Working With .ui Files

It will often happen that you need to regenerate your user interface -either because you changed your initial design, or you want to extend it. Thus writing your program's code straight in the auto-generated Perl file is quite a bad idea. You'd run constantly the risk of overwriting your handcrafted code, or end up doing lot of copy-paste.

Instead, you may :

• Write slots implementation in the Designer
  
In Qt Designer, select the Source tab of the Object Explorer. There you can see a tree-like representation of your classes. Now if you double-click on the Slots/public entry, you are prompted with a dialog where you can create a new custom slot for your module. Once this is done, the new slot appear inside the Object Explorer tree and clicking on it will bring you to a <Your Class>.ui.h file where you can write the actual implementation of your slot.

Keeping all the defaults, it should look like this :

 void Form1::newSlot()
 {
 
 }

The slot declaration is actually C++ code, but simply ignore it and write your Perl code straight between the two braces, paying special attention to indent it at least by one space.

 void Form1::newSlot()
 {
     print STDERR "Hello world from Form1::newSlot();
     if(this->foo())
     {
         # do something
     }
 }

All Perl code written this way will be saved to the ui.h file, and puic will take care of placing it back in the final program.

Here, after running puic on the Form1.ui file, you'd have:

 sub newSlot
 {
     print STDERR "Hello world from Form1::newSlot();
     if(this->foo())
     {
         # do something
     }
 }

• Subclassing your GUI
  
By using puic's -subimpl option, you may generate a derived module inheriting your original user interface.

You'd typically generate the derived module once, and write any handcrafted code in this child. Then, whenever you need to modify your GUI module, simply regenerate the parent module, and your child will inherit those changes.

To generate the base module :

 puic -o Form1.pm form1.ui

(do this as often as needed, never edit by hand)

To generate the child :

 puic -o Form2.pm -subimpl Form2 form1.ui

or

 puic -o program.pl -x -subimpl Form2 form1.ui

(do this once and work on the resulting file)

More development tools

PerlQt comes bundled with two simple programs that can help you to find your way through the Qt API:

pqtapi

pqtapi is a commandline driven introspection tool.

 usage: pqtapi [-r <re>] [<class>]

 options:
        -r <re> : find all functions matching regular expression/keyword <re>
        -i : together with -r, performs a case insensitive search
        -v : print PerlQt and Qt versions
        -h : print this help message

e.g:

 $>pqtapi -ir 'setpoint.* int'
        void QCanvasLine::setPoints(int, int, int, int)
        void QPointArray::setPoint(uint, int, int)

pqtsh

pqtsh is a graphical shell that can be used to test the API interactively. It is fairly self explanatory and includes an interactive example (Help->Example)

Known Limitations

Templated classes aren't available yet (classes derived from templated classes are).

Credits

PerlQt-3 is (c) 2002 Ashley Winters (and (c) 2003 Germain Garand)

Kalyptus and the Smoke generation engine are (c) David Faure and Richard Dale

Puic is (c) TrollTech AS., Phil Thompson and Germain Garand,

The mentioned software is released under the GNU Public Licence v.2 or later.

Appendix 1 : C++ conventions and their Perl counterpart

Whenever you want to use a class/method described in Qt's documentation (see also the 'assistant' program bundled with Qt) from PerlQt, you need to follow some simple translation rules.

Classnames

All classnames are changed from a Q prefix in Qt to a Qt:: prefix in Perl. e.g: QComboBox is named Qt::ComboBox within PerlQt.

Functions

Functions referenced as static are accessed directly, and not through an object. Thus the static function Foo in class QBar would be accessed from PerlQt as

 Qt::Bar::Foo( arg-1,...,arg-n);

The only notable exceptions are :

 qApp()     will map to Qt::app()
 qVersion() will map to Qt::version() # not really needed anymore: we have qVersion(). See Global Functions below.

Functions referenced as members or Signals are accessed through an object with the -> operator. e.g:

 $widget->show;

There are no fundamental differences between methods and signals, however PerlQt provides the emit keyword as a convenient mnemonic, so that it is clear you are emitting a signal :

 emit $button->clicked;

Arguments

• By value
  
When an argument isn't preceded by the & or * character, it is passed by value. For all basic types such as int, char, float and double, PerlQt will automatically convert litteral and scalar values to the corresponding C++ type.

Thus for a constructor prototype written as follow in the documentation :

 QSize ( int w, int h )

You'd say :

 Qt::Size(8, 12);

• By reference
  
When an argument is preceded by the & character, it means a reference to an object or to a type is expected. You may either provide a variable name or a temporary object :

 $keyseq = Qt::keySequence( &Qt::CTRL + &Qt::F3 );
 $widget->setAccel( $keyseq );
 
or

 $widget->setAccel(Qt::keySequence( &Qt::CTRL + &Qt::F3 );

If the argument isn't qualified as const (constant), it means the passed object may be altered during the process - you must then provide a variable.

• By pointer
  
When an argument is preceded by the * character, it means a pointer to an object or to a type is expected. You may provide a variable name or the Perl undef keyword for a Null pointer.

Similarly, if the argument isn't const, the passed object may be altered by the method call.

Enumerations

Enumerations are sort of named aliases for numeric values that would be hard to remember otherwise.

A C++ example would be :

 enum Strange { Apple, Orange, Lemon }

where Strange is the generic enumeration name, and Apple, Orange, Lemon its possible values, which are only aliases for numbers (here 0, 1 and 2).

Access to enumerations values in Perl Qt is very similar to a static function call. In fact, it is a static function call.

Therefore, since you probably want to avoid some readability problems, we recommend the use of the alternate function call syntax : &function.

Lets now go back to our Strange example.

If its definition was encountered in the class QFruits, you'd write from PerlQt :

 $apple_plus_orange = &Qt::Fruit::Apple + &Qt::Fruit::Orange;

Operators

Within PerlQt, operators overloading works transparently. If a given operator is overloaded in a Qt class (which means using it triggers a custom method) it will behave identically in PerlQt. Beware though that due to limitations of the Smoke binding library, not all overloaded operators are available in PerlQt. You can check the availability of a given operator by using the pqtapi program. Also, due to outstanding differences between C++'s and Perl's object paradigm, the copy constructor operator (a.k.a '=') has been disabled.

e.g-1: '+=' overload

 $p1 = Qt::Point(10, 10)
 $p2 = Qt::Point(30,40)
 $p2 += $p1; # $p2 becomes (40,50)
 
e.g-2: '<<' overload

 $f = Qt::File("example");
 $f->open( IO_WriteOnly ); # see 'Constants' below
 $s = Qt::TextStream( $f );
 $s << "What can I do with " << 12 << " apples?";

Constants

Qt doesn't use many constants, but there is at least one place where they are used : for setting Input/Output flags on files. In order to avoid the namespace pollution induced by global constants, PerlQt group them in the Qt::constants module. For instance, requesting the importation of all IO constants into the current namespace would be done with:

 use Qt::constants;

You may also import specific symbols:

 use Qt::constants qw( IO_ReadOnly IO_WriteOnly );

Global Functions

Qt has also some utilitarian functions such as bitBlt, qCompress, etc.

Those were global scope functions and have been grouped in a common namespace: Qt::GlobalSpace.

Hence, you shall access this namespace either with a fully qualified call:

 Qt::GlobalSpace::qUncompress( $buffer )

Or directly, after importation in the current namespace:

 use Qt::GlobalSpace;
 qUncompress( $buffer )

Of course, you may selectively import a few functions:

 use Qt::GlobalSpace qw( qUncompress bitBlt )

Note: GlobalSpace has also operators, such has the one performing an addition on two Qt::Point(). Those operators are called automatically.

e.g:

 $p1 = Qt::Point(10, 10) + Qt::Point(20, 20)

Appendix 2 : Internationalization

PerlQt handles internationalization by always converting QString back to utf8 in Perl.

Conversions from Perl strings to QStrings are made according to context :

• If the Perl string is already utf8-encoded
  
then the string will be converted straight to QString.

This is the most convenient and seemless way of internationalizing your application. Typically, one would just enable the use of utf8 in source code with the use utf8 pragma and write its application with an utf8 aware editor.

• If the string isn't tagged as utf8, and the use locale pragma is not set
  
then the string will be converted to QString's utf8 from ISO-Latin-1.
• If the string isn't tagged as utf8 and the use locale pragma is set
  
then the string will be converted to QString's utf8 according to the currently set locale.

Once a string contains utf8, you can convert it back to any locale by setting up converters :

 $tr1=Qt::TextCodec::codecForLocale(); # this one will use current locale
 $tr2=Qt::TextCodec::codecForName("KOI8-R"); # that one forces a specific locale (Russian)

 print $tr1->fromUnicode(Qt::DateTime::currentDateTime()->toString)."\n\n";
 print $tr2->fromUnicode($my_utf8_string);

Or, with Perl >= 5.8.0, you may use Perl's Encode modules (see perldoc Encode).

disabling utf-8

Developers who don't want to use UTF-8 or want to temporarily disable UTF-8 marshalling for handling legacy programs may use the use bytes pragma (and the corresponding no bytes).

Within the scope of this pragma, QStrings are marshalled back to ISO-Latin1 (default) or to your locale (if use locale has been set).

Frivole use of this pragma is strongly discouraged as it ruins worldwide standardization efforts.

Appendix 3 : Debugging Channels

The Qt::debug module offers various debugging channels/features.

 use Qt::debug;

 use Qt::debug qw|calls autoload verbose|;

With the simple use Qt::debug statement, the verbose and ambiguous channels are activated. If you specify a list of channels within the use statement, then only the specified channels will be enabled.

Available channels :

• ambiguous
  
Check if method and function calls are ambiguous, and tell which of the alternatives was finally elected.
• verbose
  
Enable more verbose debugging.

Together with ambiguous, tell you the nearest matches in case a method or function call fails. e.g:

 use Qt;
 use Qt::debug;
 $a= Qt::Application(\@ARGV);
 $a->libraryPath("foo");

 --- No method to call for :
        QApplication::libraryPath('foo')
 Closer candidates are :
        static void QApplication::addLibraryPath(const QString&)
        static QStringList QApplication::libraryPaths()
        static void QApplication::removeLibraryPath(const QString&)
        static void QApplication::setLibraryPaths(const QStringList&)

• calls
  
For every call, tell what corresponding Qt method is called (detailing the arguments if verbose is on).
• autoload
  
Track the intermediate code between a method invocation in Perl and its resolution to either a Qt or Perl call.
• gc
  
Give informations about garbage collection whenever a Qt object is deleted and/or a Perl object is destroyed
• virtual
  
Report whenever a virtual function tries to access its Perl reimplementation (wether it exists or not).
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Appendix 4 : Marshallers

A marshaller is a piece of ``glue code'' translating a given datatype to another.

Within PerlQt, most Qt objects keep their object nature, so that one may invoke methods on them. However, some classes and datatypes map so naturally to some Perl types that keeping their object nature would would feel unnatural and clumsy.

For instance, instead of returning a Qt::StringList object, which would require an iterator to retrieve its content, PerlQt will translate it to an array reference containing all the object's strings.

In the other way, instead of providing a Qt::StringList object as an argument of a method, one would simply provide the reference to an array of Perl strings.

Here is the list of Marshallers as of PerlQt-3.008 :

 -----------------------------------------------------------------
 float, double                         <=>       Perl real (NV)
 char, uchar, int, uint, enum
 long, ulong, short, ushort            <=>       Perl integer (IV)
 QString, -&, -*                        =>       Perl string (utf8)
 QString, -&, -*                       <=        Perl string (utf8 or iso-latin1 or locale)
 QCString, -&, -*                      <=>       Perl string (utf8 or bytes, according to content or "bytes" pragma)
 QByteArray, -&, -*                    <=>       Perl string (bytes)
 QStringList, -&, -*                    =>       Reference to an array of Perl strings (utf8)
 QString, -&, -*                        =>       Perl string (utf8 or iso-latin1 or locale)
 int&, -*                              <=>       Perl integer (IV)
 bool&, -*                             <=>       Perl boolean
 char*                                 <=>       Perl string (bytes)
 char**                                <=        Reference to an array of Perl strings (bytes)
 uchar*                                <=        Perl string (bytes)
 QRgb*                                 <=        Reference to an array of Perl integers (IV)
 QCOORD*                               <=        Reference to an array of Perl integers (IV)
 void*                                 <=>       Reference to a Perl integer (IV)
 QValueList<int>, - *, - &             <=>       Reference to an array of Perl integers (IV)
 QCanvasItemList, - *, - &              =>       Reference to an array of Qt::CanvasItem
 QWidgetList, - *, - &                 <=>       Reference to an array of Qt::Widget
 QObjectList, - *, - &                 <=>       Reference to an array of Qt::Object
 QFileInfoList, - *, - &               <=>       Reference to an array of Qt::FileInfo
 QPtrList<QTab>, - *, - &              <=>       Reference to an array of Qt::Tab
 QPtrList<QToolBar>, - *, - &          <=>       Reference to an array of Qt::ToolBar
 QPtrList<QNetworkOperation>, - *, - & <=>       Reference to an array of Qt::NetworkOperation
 QPtrList<QDockWindow>, - *, - &       <=>       Reference to an array of Qt::DockWindow
 (QUObject*)