c++ - 在同一 UI 中使用 N.2 QGraphicsView 时 QWheelEvent 不起作用

Question

我正在构建一个具有 N.2 QGraphicsView 的用户界面，并且我 只能在一个 QGraphicsView 上放大或缩小。 我正在将 QWheelEvent + CTRL 用于一个 QGraphicsView 和 QWheelEvent + ALT 用于第二个 QGraphicsView。

我阅读了非常有用的文章来开发这个程序，例如 this和 this 但所有这些都只能用于放大一个 QGraphicsView。所以 很抱歉再次写下这个问题，但我一直在努力 过去几天我正在尝试为两个不同的对象做这件事 QGraphicsView..

我包含了一段代码(主要是我使用 this post 中的代码) ) 进行缩放。请让我知道我做错了什么。

ma​​inwindow.h

private:
    Qt::KeyboardModifiers _modifiers;
    double _zoom_factor_base;
    QPointF target_scene_pos, target_viewport_pos;
    bool eventFilter(QObject* object, QEvent* event);

    Qt::KeyboardModifiers _modifiersRight;
    double _zoom_factor_base_right;
    QPointF target_scene_pos_right, target_viewport_pos_right;
    bool altDown = false;

signals:
    void zoomed();
    void zoomedRight();

protected:
    void keyPressEvent(QKeyEvent *event);
    void keyReleaseEvent(QKeyEvent *event);

ma​​inwindow.cpp

MainWindow::MainWindow(QWidget *parent) : QMainWindow(parent), ui(new Ui::MainWindow)
{    
     ui->setupUi(this);
     ui->leftView->viewport()->installEventFilter(this);
     ui->leftView->setMouseTracking(true);
     _modifiers = Qt::ControlModifier;
     _zoom_factor_base = 1.0015;
     ui->rightView->viewport()->installEventFilter(this);
     ui->rightView->setMouseTracking(true);
     _modifiersRight = Qt::ControlModifier;
     _zoom_factor_base_right = 1.0015;
}

void MainWindow::gentle_zoom(double factor)
{
     ui->leftView->scale(factor, factor);
     ui->leftView->centerOn(target_scene_pos);
     QPointF delta_viewport_pos = target_viewport_pos - QPointF(ui->leftView->viewport()->width() / 2.0,

     ui->leftView->viewport()->height() / 2.0);
     QPointF viewport_center =
     ui->leftView->mapFromScene(target_scene_pos) - delta_viewport_pos;
     ui->leftView->centerOn(ui->leftView >mapToScene(viewport_center.toPoint()));
     emit zoomed();
}
void MainWindow::set_modifiers(Qt::KeyboardModifiers modifiers)
{
     _modifiers = modifiers;
}

void MainWindow::set_zoom_factor_base(double value)
{
     _zoom_factor_base = value;
}

void MainWindow::gentle_zoom_right(double factor)
{
     ui->rightView->scale(factor, factor);
     ui->rightView->centerOn(target_scene_pos_right);
     QPointF delta_viewport_pos = target_viewport_pos_right -
     QPointF(ui->rightView->viewport()->width() / 2.0,

     ui->rightView->viewport()->height() / 2.0);
     QPointF viewport_center = ui->rightView->mapFromScene(target_scene_pos_right) - delta_viewport_pos;
     ui->rightView->centerOn(ui->rightView >mapToScene(viewport_center.toPoint())); 
     emit zoomedRight();
 }

void MainWindow::set_modifiers_right(Qt::KeyboardModifiers modifiers)
{
     _modifiersRight = modifiers;
}

void MainWindow::set_zoom_factor_base_right(double value)
{
     _zoom_factor_base_right = value;
}

bool MainWindow::eventFilter(QObject *object, QEvent *event)
{
     if (event->type() == QEvent::MouseMove)
         {
              QMouseEvent* mouse_event = static_cast<QMouseEvent*>(event);
              QPointF delta = target_viewport_pos - mouse_event->pos();
              if (qAbs(delta.x()) > 5 || qAbs(delta.y()) > 5)
              {
                  target_viewport_pos = mouse_event->pos();
                  target_scene_pos = ui->leftView->mapToScene(mouse_event->pos());
               }
         }
         else if (event->type() == QEvent::Wheel)
         {
              QWheelEvent* wheel_event = static_cast<QWheelEvent*>(event);
              if (QApplication::keyboardModifiers() == _modifiers)
              {
                  if (wheel_event->orientation() == Qt::Vertical)
                  {
                      double angle = wheel_event->angleDelta().y();
                      double factor = qPow(_zoom_factor_base_right, angle);
                      gentle_zoom(factor);
                      return true;
                  }
              }
         }
         if(altDown) // I repeat the same procedure but for the rightView
         {
              if (event->type() == QEvent::MouseMove)
              {
                   QMouseEvent* mouse_event = static_cast<QMouseEvent*>(event);
                   QPointF delta = target_viewport_pos_right - mouse_event->pos();
                   if (qAbs(delta.x()) > 5 || qAbs(delta.y()) > 5)
                   {
                        target_viewport_pos_right = mouse_event->pos();
                        target_scene_pos_right = ui->rightView->mapToScene(mouse_event->pos());
                    }
                }
                else if (event->type() == QEvent::Wheel)
                {
                    QWheelEvent* wheel_event = static_cast<QWheelEvent*>(event);
                    if (QApplication::keyboardModifiers() == _modifiersRight)
                    {
                         if (wheel_event->orientation() == Qt::Vertical)
                         {
                             double angle = wheel_event->angleDelta().y();
                             double factor = qPow(_zoom_factor_base_right, angle);
                             gentle_zoom_right(factor);
                             return true;
                         }
                    }
                }
          }
          Q_UNUSED(object)
          return false;
}

void MainWindow::keyReleaseEvent(QKeyEvent *event)
{
     if(event->key() == Qt::Key_Alt) { altDown = false; }
}

void MainWindow::keyPressEvent(QKeyEvent *event)
{
     if(event->key() == Qt::Key_Alt) { altDown = true; }
}

Answer 1

您必须了解Single responsibility principle ，它表明每个类都有自己的职责，在这种情况下可以避免出现很多困惑。缩放是QGraphicsView的责任，它不是MainWindow的责任。

为此，创建了一个继承自 QGraphicsView 的新类，并实现了缩放功能:

graphicsview.h

#ifndef GRAPHICSVIEW_H
#define GRAPHICSVIEW_H

#include <QGraphicsView>

class GraphicsView : public QGraphicsView
{
public:
    GraphicsView(QWidget *parent=nullptr);
    void setModifiers(const Qt::KeyboardModifiers &modifiers);
protected:
    void wheelEvent(QWheelEvent *event) override;
private:
    void applyZoom(double factor, const QPoint &fixedViewPos);
    Qt::KeyboardModifiers m_modifiers;
    const double base = 1.0015;
};

#endif // GRAPHICSVIEW_H

graphicsview.cpp

#include "graphicsview.h"

#include <QWheelEvent>
#include <QtMath>

GraphicsView::GraphicsView(QWidget *parent):
    QGraphicsView(parent)
{}

void GraphicsView::setModifiers(const Qt::KeyboardModifiers &modifiers)
{
    m_modifiers = modifiers;
}

void GraphicsView::wheelEvent(QWheelEvent *event)
{
    if(event->modifiers() == m_modifiers){
        double angle = event->orientation() == Qt::Vertical ? event->angleDelta().y(): event->angleDelta().x();
        double factor = qPow(base, angle);
        applyZoom(factor, event->pos());
    }
}

void GraphicsView::applyZoom(double factor, const QPoint & fixedViewPos)
{
    QPointF fixedScenePos = mapToScene(fixedViewPos);
    centerOn(fixedScenePos);
    scale(factor, factor);
    QPointF delta = mapToScene(fixedViewPos) - mapToScene(viewport()->rect().center());
    centerOn(fixedScenePos - delta);
}

然后使用小部件promotion由 Qt Designer 提供的插入到 GUI 中。然后设置值:

ui->rightView->setModifiers(Qt::AltModifier);
ui->leftView->setModifiers(Qt::ControlModifier);

完整的示例可以在 here 找到.

---

另一方面，SO 中显示的许多代码示例只是为了展示功能，并不一定用于项目的实现，因为这里的空间很小，有时会被压缩而失去可读性。例如，我基于您指出的答案的想法，但我已正确划分它以获得干净的代码。