How do events work in Qt?

Question

I have some questions about the general usage of Qt events. I'm new to Qt, and I am going to try out making a custom event. The questions I ask are related to this article: Qt 4.8: The Event System

• When does an event “occur”?
  In Qt's built in events, mouse clicks and key presses are put into a queue and then the functions are executed at the next frame. I'm especially wondering about this for custom events, because I'm not sure if it always occurs when a mouse is clicked. For custom events, is it when you send the event into the queue and then waits to be processed by the event() function at the next frame?

• To create a custom event, must you make a class that inherits from QEvent and register an event with registerEventType() function?
  Is this the standard process, or can an event simply be a class? How does this function, registerEventType(), work?

• Do custom events have a QEvent::Type?
  Is this the number between 1000 and 6563 that is given when using the registerEventType() function?

• What is the recipient of an event?
  It seems to be in functions' parameters like postEvent(), sendEvent(), etc. However, I am not sure what this object is for.

• Where is the actual code that is executed when an event is fired?
  Is it a function, or is it in the event() function of QObjects.

Also any working examples of Qt events (both built-in or custom) in action would be helpful.

Answer 1

You should look at Qt Examples online or in QtSDK, there are tons of them. IMO you didn't search hard.

Ad.1. It occurs after you fire it with QApplication::postEvent() or QApplication::sendEvent(). Not immediately of course, because it has to go through the main loop, etc. The order of events should be preserved, though.

Ad.2. Look at this , second anwser.

Ad.3. Go to Ad.2.

Ad.4. This object will receive this custom event in QObject::customEvent() handler.

Ad.5. Go to Ad.4.