Difference between revisions of "FPC and Qt"
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== Introduction == | == Introduction == | ||
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This piece of code is taken from the second package mentioned above. | This piece of code is taken from the second package mentioned above. | ||
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app: QApplicationH; | app: QApplicationH; | ||
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| − | If you know Qt used in C++, you can see that there is not much difference. | + | If you know how Qt is used in C++, you can see that there is not much difference. |
Latest revision as of 02:03, 16 February 2020
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Introduction
There are a number of Qt bindings available:
Qt3
Another QtC based binding by Andreas
The first one aims on linux/unix users while the second one is for win32.
Qt/Embedded
The FPC arm port and this Qt/E binding allow graphical programming on devices such as the Zaurus
Qt4
More recently a small Qt4 Binding is available. It does not depend on the obsolete QtC library. The Qt4 binding page will provide more information on how the binding works and how to use it.
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 package 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 how Qt is used in C++, you can see that there is not much difference.
