How do I get the mouse event in Qt?
Mouse move events will occur only when a mouse button is pressed down, unless mouse tracking has been enabled with QWidget::setMouseTracking(). Qt automatically grabs the mouse when a mouse button is pressed inside a widget; the widget will continue to receive mouse events until the last mouse button is released.
What is a QEvent?
The QEvent class is the base class of all event classes. Event objects contain event parameters. Qt’s main event loop (QCoreApplication::exec()) fetches native window system events from the event queue, translates them into QEvents, and sends the translated events to QObjects.
What is eventFilter in Qt?
An event filter gets to process events before the target object does. The filter’s QObject::eventFilter() implementation is called, and can accept or reject the filter, and allow or deny further processing of the event.
How do I create a Qt event?
Qt applications can generate their own events, either of predefined types or of custom types. This is done by creating an instance of QEvent (or a subclass) and calling QApplication::postEvent() or QApplication::sendEvent(). Both functions take a QObject * and a QEvent * as arguments.
What is Paintevent?
The Paint event is raised when the control is redrawn. It passes an instance of PaintEventArgs to the method(s) that handles the Paint event. When creating a new custom control or an inherited control with a different visual appearance, you must provide code to render the control by overriding the OnPaint method.
What is event loop in Qt?
Qt’s event loop starts the moment the underlying application’s exec() function gets called. Once started, the loop repeatedly checks for something to happen in the system, such as user-input through keyboard/mouse.
How do you use QTimer?
The QTimer class provides a high-level programming interface for timers. To use it, create a QTimer, connect its timeout() signal to the appropriate slots, and call start(). From then on, it will emit the timeout() signal at constant intervals.
How do you use QThread?
To use it, prepare a QObject subclass with all your desired functionality in it. Then create a new QThread instance, push the QObject onto it using moveToThread(QThread*) of the QObject instance and call start() on the QThread instance. That’s all.
How does an event loop work?
The event loop is a process that waits for the Call Stack to be clear before pushing callbacks from the Task Queue to the Call Stack. Once the Stack is clear, the event loop triggers and checks the Task Queue for available callbacks.
Is QObject thread safe?
QObject and all of its subclasses are not thread-safe. This includes the entire event delivery system. It is important to keep in mind that the event loop may be delivering events to your QObject subclass while you are accessing the object from another thread.
How accurate is QTimer?
Most platforms support a resolution of 1 millisecond, though the accuracy of the timer will not equal this resolution in many real-world situations. The accuracy also depends on the timer type. For Qt::PreciseTimer, QTimer will try to keep the accurance at 1 millisecond.