QMouseEvent mouse event theory
I. Overview
Mouse events occur when the mouse button is pressed or released , or the mouse cursor is moved , within the QWidget window .
There is nothing special about mouse press and release, but mouse move events are special. Mouse move events will only occur when the mouse button is pressed , unless mouse tracking is enabled using the QWidget::setMouseTracking() function.
- QWidget::setMouseTracking(bool enable)
If mouse tracking is disabled (default), the Widget will only receive mouse movement events if at least one mouse button is pressed during mouse movement.
If mouse tracking is enabled, the widget will receive mouse movement events even when no button is pressed.
Second, the transmission of mouse events
When the mouse button inside the widget is pressed, Qt will automatically grab the mouse; the widget will continue to receive mouse events until the last mouse button is released.
Mouse events contain a special accept flag that indicates whether the receiver wants the event. If the widget does not handle mouse events, ignore() should be called. This operation allows the mouse event to propagate up the parent Widget chain until the Widget accepts it using accept(), or the event filter consumes it.
Note: If a mouse event is propagated to a Widget with Qt::wa_nomoussepropagation set, the mouse event will not be propagated further up the parent Widget chain.
3. Combination modifiers
The state of keyboard modifier keys can be found by calling the modifiers() function inherited from QInputEvent.
It's like I hold down some shift or alt while the mouse is moving. This can be when multiple keys are pressed at the same time,
| identification name | value | meaning |
|---|---|---|
| Qt::NoModifier | 0x00000000 | no modifier keys pressed |
| Qt::ShiftModifier | 0x02000000 | Shift press |
| Qt::ControlModifier | 0x04000000 | Ctrl pressed |
| Qt::AltModifier | 0x08000000 | Alt press |
| Qt::MetaModifier | 0x10000000 | Meta press |
4. Mouse coordinate position
The functions pos(), x() and y() give the position of the mouse relative to the Widget receiving the mouse event.
If the Widget is moved after a mouse event, use the global position returned by globalPos() to avoid jittering. This globalPos() is actually the position of the mouse on the entire screen plane, and pos() refers to the position of the mouse in this window.
5. How to use
The function QWidget::setEnabled() can be used to enable or disable the mouse and keyboard events of the Widget.
When using this event function, you need to reimplement the QWidget event handler, that is, inherit the QWidget window to rewrite QWidget::mousePressEvent(), QWidget::mouseReleaseEvent(), QWidget::mouseDoubleClickEvent() and QWidget::mouseMoveEvent( ), you can receive mouse events in your own Widget. Of course, you don't need to inherit, you can also use the event filter directly.