SizeGripItem

SizeGripItem

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c++ - 如果选择了该项，为什么QGraphicsItem的子级不再获得鼠标单击？

我在SizeGripItem的子类上使用了here的QGraphicsRectItem(进行了最小的修改以添加信号)，如下所示:
header 

//! RectItem that sends a boxChanged signal whenever it is moved or resized via the handles.
class QSignalingBoxItem : public QObject, public QGraphicsRectItem
{
    Q_OBJECT

private:
    void setSelected_(bool selected);

protected:
    QVariant itemChange(GraphicsItemChange change, const QVariant & value);

public:
    QSignalingBoxItem(QRectF rect, QGraphicsItem * parent = nullptr);
    ~QSignalingBoxItem();

signals:
    void boxChanged(QRectF newBox);
};
.cpp
namespace
{
    class BoxResizer : public SizeGripItem::Resizer
    {
    public:
        virtual void operator()(QGraphicsItem* item, const QRectF& rect)
        {
            QSignalingBoxItem* rectItem =
                dynamic_cast<QSignalingBoxItem*>(item);

            if (rectItem)
            {
                rectItem->setRect(rect);
            }
        }
    };
}

QSignalingBoxItem::QSignalingBoxItem(QRectF rect, QGraphicsItem * parent) : QGraphicsRectItem(parent)
{
    setFlags(QGraphicsItem::ItemIsMovable |
             QGraphicsItem::ItemIsSelectable |
             QGraphicsItem::ItemSendsScenePositionChanges);
}

QVariant QSignalingBoxItem::itemChange(GraphicsItemChange change, const QVariant & value)
{
    switch (change)
    {
    case QGraphicsItem::ItemSelectedHasChanged:
        setSelected_(value.toBool());
        break;
    case QGraphicsItem::ItemScenePositionHasChanged:
        emit boxChanged(rect());
        break;
    default:
        break;
    }
    return value;
}

void QSignalingBoxItem::setSelected_(bool selected)
{
    //TODO: Test that it works as expected
    if (selected)
    {
        auto sz = new SizeGripItem(new BoxResizer, this);
        connect(sz, &SizeGripItem::resized, [&]() {emit boxChanged(rect()); });
    }
    else
    {
        // Get the child
        // If it's a SizeGripItem, delete it.
        if (childItems().length() > 0)
        {
            foreach(QGraphicsItem* item, childItems())
            {
                auto sz = dynamic_cast<SizeGripItem*>(item);
                if (sz)
                {
                    delete sz;
                    break;
                }
            }
        }
    }
}
如果我在构造函数中应用SizeGripItem，则该类将按预期工作。但是，我需要使句柄可见并且仅在选中该项目时才起作用。但是，当我运行上面的代码时，会显示手柄，但是单击手柄会移动整个框(就像我在框的中间单击一样)而不是调整其大小。
使用调试器运行时，我发现itemChange甚至没有被调用。
为什么会这样呢？以及选择该项目后，我该如何修改类以使其正常工作？
编辑
这就是使用该类的方式。我使用自己的私有(private)QGraphicsView扩展了m_scene，在其中我重写mouse{Press,Move,Release}Event来通过“单击并拖动”生成一个框。
撇开该类的其余部分，因为它唯一涉及QSignalingBoxItem的部分是这三个函数，所以我添加了它们。如果需要更多，我将根据需要添加。
void QSampleEditor::mousePressEvent(QMouseEvent * mouseEvent)
{
    QImageView::mousePressEvent(mouseEvent);
    if (mouseEvent->buttons() == Qt::RightButton && m_currentSample && m_activePixmap && m_activePixmap->isUnderMouse())
    {
        m_dragStart = mapToScene(mouseEvent->pos());
        m_currentBox = new QSignalingBoxItem({ m_dragStart, QSize(0,0) });
        m_scene.addItem(m_currentBox);
        mouseEvent->accept();
    }
}

void QSampleEditor::mouseMoveEvent(QMouseEvent * mouseEvent)
{
    QImageView::mouseMoveEvent(mouseEvent);
    if (m_currentBox)
    {
        m_currentBox->setRect(rectFromTwoPoints(m_dragStart, mapToScene(mouseEvent->pos())));
        mouseEvent->accept();
    }
}

void QSampleEditor::mouseReleaseEvent(QMouseEvent * mouseEvent)
{
    //TODO: Add checks that the sample is still there.

    QImageView::mouseReleaseEvent(mouseEvent);
    if (m_currentBox)
    {
        // Add to the StringSample
        auto new_char = new CharacterSample;
        connect(m_currentBox, &QSignalingBoxItem::boxChanged, new_char, &CharacterSample::boxChanged);
        new_char->boxChanged(m_currentBox->rect());
        m_currentSample->addCharacter(new_char);
        m_currentBox = nullptr;
        mouseEvent->accept();
    }
}

最佳答案

当给定项目的任何可移动祖先项目被选中时，最老的被选择祖先将接收事件-即使该项目的位置与子项目重叠。这是在 QGraphicsItem::mouseMoveEvent 中处理的-如果可移动祖先存在，则不处理的move事件。最老的可移动选定祖先接收到该事件并使用该事件进行自身移动，但后代项将忽略该事件(此处为句柄!)。
有关代码的一般说明(您和您正在重用的代码):

  • 以Q开头的类型名称保留用于Qt。除非已将Qt放在命名空间中，否则不应使用此类名称。
  • 应该将SizeGripItem标记为不包含任何内容-因为其paint方法是禁止操作的。
  • 通过const引用传递非数字，非指针的方法参数，除非该方法需要内部修改的副本。
  • SizeGripItem需要具有Resizer或发出信号，而不能同时具有两者-这两个选项是互斥的。
    实际上，Resizer是Qt 4痕迹，其中的插槽非常冗长，无法连接到lambda。在Qt 5中完全没有必要将信号连接到任何函子，包括Resizer类型的函子，从而使QObject::connect与Resizer(!)的显式使用隐式地向后兼容。

    • 可以提出以下解决方案:
  • 一个简单的解决方案-这消除了问题的主要原因:使被管理项目不可移动。手柄将起作用。它与选择状态无关。导致问题的原因是可移动性。
  • 使SizeGripItem本身可移动。 SignalingBoxItem无法移动。
  • 重新实现SizeGripItem::HandleItem的mouseMoveEvent以接受相关事件并对其使用react。 SignalingBoxItem仍可移动。
  • 将SizeGripItem用作其HandleItem的事件过滤器，并像解决方案2中一样处理相关事件。 SignalingBoxItem仍可移动。
  • 使SizeGripItem是SignalingBoxItem的同级。这样，SignalingBoxItem可以是可移动的，而不会影响SizeGripItem的句柄的使用。当然，然后SignalingBoxItem的祖先就不能移动了。

    • 以下是约240行的完整示例，实现了解决方案1-3。每个解决方案都在条件块中描述，并且示例在启用它们的任何子集的情况下进行编译。没有选择解决方案，原来的问题仍然存在。可以在运行时选择启用的解决方案。
    首先，让我们从 SizeGripItem 开始:
    // https://github.com/KubaO/stackoverflown/tree/master/questions/graphicsscene-children-51596611
#include <QtWidgets>
#include <array>
#define SOLUTION(s) ((!!(s)) << (s))
#define HAS_SOLUTION(s) (!!(SOLUTIONS & SOLUTION(s)))
#define SOLUTIONS (SOLUTION(1) | SOLUTION(2) | SOLUTION(3))

class SizeGripItem : public QGraphicsObject {
   Q_OBJECT
   enum { kMoveInHandle, kInitialPos, kPressPos };
   struct HandleItem : QGraphicsRectItem {
      HandleItem() : QGraphicsRectItem(-4, -4, 8, 8) {
         setBrush(Qt::lightGray);
         setFlags(ItemIsMovable | ItemSendsGeometryChanges);
      }
      SizeGripItem *parent() const { return static_cast<SizeGripItem *>(parentItem()); }
      QVariant itemChange(GraphicsItemChange change, const QVariant &value) override {
         if (change == ItemPositionHasChanged) parent()->handleMoved(this);
         return value;
      }
#if HAS_SOLUTION(2)
      bool sceneEvent(QEvent *event) override {
         return (data(kMoveInHandle).toBool() && hasSelectedMovableAncestor(this) &&
                 processMove(this, event)) ||
                QGraphicsRectItem::sceneEvent(event);
      }
#endif
   };
#if HAS_SOLUTION(2) || HAS_SOLUTION(3)
   static bool processMove(QGraphicsItem *item, QEvent *ev) {
      auto mev = static_cast<QGraphicsSceneMouseEvent *>(ev);
      if (ev->type() == QEvent::GraphicsSceneMousePress &&
          mev->button() == Qt::LeftButton) {
         item->setData(kInitialPos, item->pos());
         item->setData(kPressPos, item->mapToParent(mev->pos()));
         return true;
      } else if (ev->type() == QEvent::GraphicsSceneMouseMove &&
                 mev->buttons() == Qt::LeftButton) {
         auto delta = item->mapToParent(mev->pos()) - item->data(kPressPos).toPointF();
         item->setPos(item->data(kInitialPos).toPointF() + delta);
         return true;
      }
      return false;
   }
   static bool hasSelectedMovableAncestor(const QGraphicsItem *item) {
      auto *p = item->parentItem();
      return p && ((p->isSelected() && (p->flags() & QGraphicsItem::ItemIsMovable)) ||
                   hasSelectedMovableAncestor(p));
   }
#endif
   std::array<HandleItem, 4> handles_;
   QRectF rect_;
   void updateHandleItemPositions() {
      static auto get = {&QRectF::topLeft, &QRectF::topRight, &QRectF::bottomLeft,
                         &QRectF::bottomRight};
      for (auto &h : handles_) h.setPos((rect_.*get.begin()[index(&h)])());
   }
   int index(HandleItem *handle) const { return handle - &handles_[0]; }
   void handleMoved(HandleItem *handle) {
      static auto set = {&QRectF::setTopLeft, &QRectF::setTopRight,
                         &QRectF::setBottomLeft, &QRectF::setBottomRight};
      auto rect = rect_;
      (rect.*set.begin()[index(handle)])(handle->pos());
      setRect(mapRectToParent(rect.normalized()));
   }

  public:
   SizeGripItem(QGraphicsItem *parent = {}) : QGraphicsObject(parent) {
      for (auto &h : handles_) h.setParentItem(this);
      setFlags(ItemHasNoContents);
   }
   QVariant itemChange(GraphicsItemChange change, const QVariant &value) override {
      if (change == QGraphicsItem::ItemPositionHasChanged) resize();
      return value;
   }
   void paint(QPainter *, const QStyleOptionGraphicsItem *, QWidget *) override {}
   QRectF boundingRect() const override { return rect_; }
   void setRect(const QRectF &rect) {
      rect_ = mapRectFromParent(rect);
      resize();
      updateHandleItemPositions();
   }
   void resize() { emit rectChanged(mapRectToParent(rect_), parentItem()); }
   Q_SIGNAL void rectChanged(const QRectF &, QGraphicsItem *);
#if SOLUTIONS
   void selectSolution(int i) {
#if HAS_SOLUTION(1)
      setFlag(ItemIsMovable, i == 1);
      setFlag(ItemSendsGeometryChanges, i == 1);
      if (i != 1) {
         auto rect = mapRectToParent(rect_);
         setPos({});  // reset position if we're leaving the movable mode
         setRect(rect);
      }
      i--;
#endif
      for (auto &h : handles_) {
         int ii = i;
#if HAS_SOLUTION(2)
         h.setData(kMoveInHandle, ii-- == 1);
#endif
#if HAS_SOLUTION(3)
         if (ii == 1)
            h.installSceneEventFilter(this);
         else
            h.removeSceneEventFilter(this);
#endif
      }
   }
#endif
#if HAS_SOLUTION(3)
   bool sceneEventFilter(QGraphicsItem *item, QEvent *ev) override {
      if (hasSelectedMovableAncestor(item)) return processMove(item, ev);
      return false;
   }
#endif
};
    然后，SignalingBoxItem:
    class SignalingBoxItem : public QObject, public QGraphicsRectItem {
   Q_OBJECT
   SizeGripItem m_sizeGrip{this};
   QVariant itemChange(GraphicsItemChange change, const QVariant &value) override {
      if (change == QGraphicsItem::ItemSelectedHasChanged)
         m_sizeGrip.setVisible(value.toBool());
      else if (change == QGraphicsItem::ItemScenePositionHasChanged)
         emitRectChanged();
      return value;
   }
   void emitRectChanged() { emit rectChanged(mapRectToScene(rect())); }
   void setRectImpl(const QRectF &rect) {
      QGraphicsRectItem::setRect(rect);
      emitRectChanged();
   }

  public:
   SignalingBoxItem(const QRectF &rect = {}, QGraphicsItem *parent = {})
       : QGraphicsRectItem(rect, parent) {
      setFlags(ItemIsMovable | ItemIsSelectable | ItemSendsScenePositionChanges);
      m_sizeGrip.hide();
      connect(&m_sizeGrip, &SizeGripItem::rectChanged, this,
              &SignalingBoxItem::setRectImpl);
   }
   void setRect(const QRectF &rect) {
      setSelected(false);
      m_sizeGrip.setRect(rect);
      setRectImpl(rect);
   }
   Q_SIGNAL void rectChanged(const QRectF &);  // Rectangle in scene coordinates
#if SOLUTIONS
   void selectSolution(int index) {
      setFlag(ItemIsMovable, !HAS_SOLUTION(1) || index != 1);
      m_sizeGrip.selectSolution(index);
   }
#endif
};
    SampleEditor:
    class SampleEditor : public QGraphicsView {
   Q_OBJECT
   bool m_activeDrag = false;
   SignalingBoxItem m_box;
   QPointF m_dragStart;

  public:
   SampleEditor(QGraphicsScene *scene) : QGraphicsView(scene) {
      scene->addItem(&m_box);
      connect(&m_box, &SignalingBoxItem::rectChanged, this, &SampleEditor::rectChanged);
   }
   Q_SIGNAL void rectChanged(const QRectF &);
   void mousePressEvent(QMouseEvent *event) override {
      QGraphicsView::mousePressEvent(event);
      if (event->button() == Qt::RightButton) {
         m_dragStart = m_box.mapFromScene(mapToScene(event->pos()));
         m_activeDrag = true;
         m_box.show();
         m_box.setRect({m_dragStart, m_dragStart});
         event->accept();
      }
   }
   void mouseMoveEvent(QMouseEvent *event) override {
      QGraphicsView::mouseMoveEvent(event);
      if (m_activeDrag) {
         m_box.setRect({m_dragStart, m_box.mapFromScene(mapToScene(event->pos()))});
         event->accept();
      }
   }
   void mouseReleaseEvent(QMouseEvent *event) override {
      QGraphicsView::mouseReleaseEvent(event);
      if (m_activeDrag && event->button() == Qt::RightButton) {
         event->accept();
         m_activeDrag = false;
      }
   }
   void resizeEvent(QResizeEvent *event) override {
      QGraphicsView::resizeEvent(event);
      scene()->setSceneRect(contentsRect());
   }
#if SOLUTIONS
   void selectSolution(int index) { m_box.selectSolution(index); }
#endif
};
    最后，演示代码:
    int main(int argc, char *argv[]) {
   QApplication a(argc, argv);
   QWidget ui;
   QGridLayout layout{&ui};
   QGraphicsScene scene;
   SampleEditor editor(&scene);
   QComboBox sel;
   QLabel status;
   layout.addWidget(&editor, 0, 0, 1, 2);
   layout.addWidget(&sel, 1, 0);
   layout.addWidget(&status, 1, 1);
   sel.addItems({
      "Original (Movable SignalingBoxItem)",
#if HAS_SOLUTION(1)
          "Movable SizeGripItem",
#endif
#if HAS_SOLUTION(2)
          "Reimplemented HandleItem",
#endif
#if HAS_SOLUTION(3)
          "Filtering SizeGripItem",
#endif
   });
   sel.setCurrentIndex(-1);
#if SOLUTIONS
   QObject::connect(&sel, QOverload<int>::of(&QComboBox::currentIndexChanged),
                    [&](int index) { editor.selectSolution(index); });
#endif
   QObject::connect(&editor, &SampleEditor::rectChanged, &status,
                    [&](const QRectF &rect) {
                       QString s;
                       QDebug(&s) << rect;
                       status.setText(s);
                    });
   sel.setCurrentIndex((sel.count() > 1) ? 1 : 0);
   ui.setMinimumSize(640, 480);
   ui.show();
   return a.exec();
}
#include "main.moc"

    关于c++ - 如果选择了该项，为什么QGraphicsItem的子级不再获得鼠标单击？，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/51596611/

    10-10 21:21
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