How-to-use-signals-and-slots: Difference between revisions

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'''English''' [[Signal Slot yapisini Anlamak|Türkçe]]
#REDIRECT [[Qt_signal-slot_quick_start]]
 
==Introduction==
 
Remember old X-Window ''call-back'' system? Generally it isn’t type safe and flexible. There are many problems with them. Qt offer new event-handling system – ''signal-slot'' connections. Imagine alarm clock. When alarm is ringing, signal is sending (''emitting''). And you’re handling it as a slot.
 
# Every QObject class may have as many signals of slots as you want.
# You can emit signal only from that class, where signal is.
# You can ''connect'' signal with another signal (make chains of signals);
# Every signal and slot can have unlimited count of connections with other.
# '''<span class="caps">ATTENTION</span>!''' You can’t set default value in slot attributes. ''e.g.'' <code>void mySlot(int i = 0);</code>
 
==Connection==
 
You can connect signal with this template:<br /> You have to wrap ''const char * signal'' and ''const char * method'' into <span class="caps">SIGNAL</span> and <span class="caps">SLOT</span> macros.
 
And you also can disconnect signal-slot:<br />
 
==Deeper==
 
Widgets emit signals when events occur. For example, a button will emit a “clicked” signal when it is clicked. A developer can choose to connect to a signal by creating a function (a “slot”) and calling the <code>connect()</code> function to relate the signal to the slot. Qt’s signals and slots mechanism does not require classes to have knowledge of each other, which makes it much easier to develop highly reusable classes. Since signals and slots are type-safe, type errors are reported as warnings and do not cause crashes to occur.
 
For example, if a Quit button’s <code>clicked()</code> signal is connected to the application’s <code>quit()</code> slot, a user’s click on Quit makes the application terminate. In code, this is written as
 
Connections can be added or removed at any time during the execution of a Qt application, they can be set up so that they are executed when a signal is emitted or queued for later execution, and they can be made between objects in different threads.
 
The signals and slots mechanism is implemented in standard C++. The implementation uses the C++ preprocessor and <code>moc</code>, the Meta-Object Compiler, included with Qt. Code generation is performed automatically by sub:Qt’s-Build-System. Developers never have to edit or even look at the generated code.
 
In addition to handling signals and slots, the Meta-Object Compiler supports Qt’s translation mechanism, its property system, and its extended run-time type information. It also makes run-time introspection of C++ programs possible in a way that works on all supported platforms.

Latest revision as of 07:13, 27 February 2015

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