FPC and Qt

Introduction

Since a few months, there are now Qt3 interface units available for FPC. There are two different packages available:

http://www.theo.ch/kylix/Qt3pas.zip

http://andy.jgknet.de/oss/qt/qt3forFPC/

The first one aims on linux/unix users while the second one is for win32.

There is also a binding to Qt/Embedded for the FPC arm port that can be used on devices such as the Zaurus

http://users.pandora.be/Jan.Van.hijfte/qtforfpc/qtedemo.html

How it works

FPC still can't use C++ classes natively so these interface units use the same scheme as e.g. the official C interface to Qt does: there are wrapper procedures written which export an procedural interface. This procedural interface is wrapped by an object pascal interface again to make usage easier.

This might sound like an huge overhead but these wrapper are mainly necessary to hide name mangling differences so there shouldn't be a noticable speed decrease in real world applications.

Example

This piece of code is taken from the second of these two packages mentioned above.

var
  app: QApplicationH;
  btn: QPushButtonH;
begin
  // create static ( interfaced handled ) QApplicationH
  app := NewQApplicationH(ArgCount, ArgValues).get;
  // due to a bug in fpc 1.9.5 the WideString helper methods with default parameter are disabled
  //btn := NewQPushButtonH('Quit', nil).get;
  btn := NewQPushButtonH(qs('Quit').get, nil, nil).get;
  btn.setGeometry(100, 100, 300, 300);
  btn.show;
  // override the virtual eventFilter method of btn
  btn.OverrideHook.eventFilter := @TTest.MyEventFilter;
  // and install the btn as it's own eventFilter
  btn.installEventFilter(btn);
  // connect Qt signal to Qt slot
  QObjectH.connect(btn, SIGNAL('clicked()'), app, SLOT('quit()'));
  ...

If you know Qt used in C++, you might see, that there is no much difference.