QT | mouse events and wheel events qmouseevent, qwheelevent

Preface ：

Mouse events are often used in programs , Realize different functions according to different mouse events . stay Qt in ,QMouseEvent Class represents mouse events . Some custom operations are usually carried out by redefining the mouse event handler function of the part .QWheelEvent Class to represent mouse wheel events , It is mainly used to obtain the rolling direction and distance of the roller .

Mouse events ：

The mouse events we usually use are ：

• void mousePressEvent(QMouseEvent *event); // Mouse button down

• void mouseReleaseEvent(QMouseEvent *event); // Mouse button up

• void mouseDoubleClickedEvent(QMouseEvent *event); // Double click the mouse button

• void mouseMouveEvent(QMouseEvent *event); // Mouse movement

• void wheelEvent(QWheelEvent *event); // Scroll with the mouse wheel

stay QWidget The definition in is shown in the figure ：

Mouse movement events ：

• Mouse movement event mouseMouveEvent() The default is when the mouse button is pressed and the mouse is moved ;

• If you don't want to press the mouse to get the mouse movement event , You need to add ：
• setMouseTracking(true);// Set mouse tracking

Set the mouse shape ：

1. Set the shape provided by the mouse for the system ：

QCursor cursor;
cursor.setShape(Qt::OpenHandCursor);// Small palm shape
setCursor(cursor);
// Or use ：QApplication::setOverriedCursor(cursor);// Make the mouse pointer temporarily change shape


Qt Common mouse pointer shapes are provided in , You can help through Qt::CursorShape Keyword view .

2. Set the mouse to a custom shape ：

QCursor cursor("./image/logo.png");
setCursor(cursor);
// Or use ：QApplication::setOverrideCursor(cursor);// Make the mouse pointer temporarily change shape


If used QApplication::setOverriedCursor(cursor); To temporarily change the shape of the mouse pointer , Then you need to use when restoring the mouse shape QApplication::restoreOverrideCursor();

Q_UNUSED():

If the parameters passed in from the function are not used in the function , For example, in void mousePressEvent(QMouseEvent *event) Function body , We didn't use event This parameter , In this way, a warning will appear when compiling the program , But this will not affect the compilation and operation of the program , If you don't want such a warning message , You can add Q_UNUSED(xxx);xxx Indicates parameters that are not used . So there's no warning .

Wheel event ：

• QWheelEvent() Class delta() Function returns the distance the scroll wheel moves .

• Whenever the roller rotates , The default is 15 degree , Call at this time QWheelEvent()::delta() The value returned is 15*8=120.

• The direction of rotation is outward , Returns a positive value ; The direction of rotation is inward , Returns a negative value . So you can judge the direction of the roller by the positive and negative return value of this function .

Drag the mouse to move the window ：

void Widget::mousePressEvent(QMouseEvent *event)
{
 if(event->button() == Qt::LeftButton) //  Left mouse button
 {
 m_isMouseLeftDown = true;
 m_dragPos = event->globalPos() - pos(); // Get the difference between the pointer position and the window position
 }
}

void Widget::mouseMoveEvent(QMouseEvent *event)
{
 if(event->buttons() & Qt::LeftButton)// See note ：
 {
 move(event->globalPos() - m_dragPos);
 event->accept(); // Event handler “ receive ” The incident happened , Do not pass to the parent part ;
 }
}


notes ：

Because when the mouse moves, it will detect all the pressed keys , And then use QMouseEvent Of button() The function cannot get which key was pressed , Only use buttons() function , So want to use buttons() and Qt::LeftButton Perform bitwise and operation to determine whether the left mouse button is pressed .

Realize the scroll wheel to enlarge or shrink the content in the editor ：

void Widget::wheelEvent(QWheelEvent *event)
{
 if(event->delta() > 0)
 {
 ui->textEdit->zoomIn();// Zoom in
 }
 else
 {
 ui->textEdit->zoomOut();// narrow
 }
}