图形项目的QgraphicsScene中的可拖动像素

Question

我有一个带有12*4网格的场景，带有Qgraphictems块，当我右键单击这些块时，我有一个contexmenu 可以在块中添加图标，我的主张是我不能说出如何使这些图标可将这些图标拖到图形场景中的其他块，我知道有"可拖动图标示例"，但是如何将该代码实现到图形场景。

这是mainwindow.h

#ifndef MAINWINDOW_H
#define MAINWINDOW_H
#include <QMainWindow>
#include <QGraphicsPathItem>
class QGraphicsSceneMouseEvent;
namespace Ui {
class MainWindow;
}
class MainWindow : public QMainWindow
{
Q_OBJECT
public:
explicit MainWindow(QWidget *parent = 0);
bool eventFilter(QObject *, QEvent *);
~MainWindow();
private slots:
void showContextMenu(const QPoint&);
void addPixBlock();
private:
Ui::MainWindow *ui;
QGraphicsScene *scene;
QGraphicsItem *itemAt(const QPointF&);
int x;
int y;
QMenu *Menu;
QMenu *Submenu;
QAction *Picture;
QGraphicsPixmapItem* pix;
};
#endif // MAINWINDOW_H

mainwindow.cpp

#include "mainwindow.h"
#include "ui_mainwindow.h"
#include "block.h"
#include <QGraphicsScene>
#include <QGraphicsSceneMouseEvent>
#include <QDebug>
#include <QPainter>
MainWindow::MainWindow(QWidget *parent) :
QMainWindow(parent),
ui(new Ui::MainWindow)
{
ui->setupUi(this);
scene = new QGraphicsScene(this) ;
for(int row=-4;row<8;++row)
  for(int column=0;column<4;++column)
{
  Block *b = new Block;
  scene->addItem(b);
  b->setPos(row* 95,column*85);
}
ui->graphicsView->setScene(scene);
scene->installEventFilter(this);
}
MainWindow::~MainWindow()
{
delete ui;
}
QGraphicsItem* MainWindow::itemAt(const QPointF &pos)
{
QList<QGraphicsItem*> items = scene->items(QRectF(pos - QPointF(1,1), 
QSize(3,3)));
foreach(QGraphicsItem *item, items)
     if (item->type() > QGraphicsItem::UserType)
     return item;
 return 0;
  }
 bool MainWindow::eventFilter(QObject *o, QEvent *e)
  {
 QGraphicsSceneMouseEvent *me = (QGraphicsSceneMouseEvent*) e;
 switch ((int) e->type()){
 case QEvent::GraphicsSceneMousePress:{
 switch ((int) me->button()){
  case Qt::RightButton:{
     QGraphicsItem *item = itemAt(me->scenePos());
     if (item && item->type() == Block::Type){
         x=item->scenePos().x();
         y=item->scenePos().y();
        showContextMenu(item->scenePos().toPoint());
      }
   break;
  }
  }
  break;
  }
 }
 return QObject::eventFilter(o, e);
 }
void MainWindow::showContextMenu(const QPoint &pos)
{
Menu= new QMenu("Menu");
Submenu=Menu->addMenu(QIcon(":/img/pix.png"),"Pix");
Picture =Submenu->addAction(QIcon(":/img/pix.png"),"Pix");
connect(Picture, SIGNAL(triggered()), this, SLOT(addPixBlock()));
Menu->exec(QCursor::pos());
}
void MainWindow::addPixBlock()
{
QPixmap pixmap(":/img/pix.png");
pix = scene->addPixmap(pixmap.scaled(70,50));
pix->setPos(x,y);
}

块。H

#ifndef BLOCK_H
#define BLOCK_H
#include <QGraphicsPathItem>
class QGraphicsSceneMouseEvent;
class Block : public QGraphicsPathItem
{
public:
enum { Type = QGraphicsItem::UserType + 3 };
int type() const { return Type; }
Block(QGraphicsItem *parent = 0);
void paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget 
*widget);
bool eventFilter(QObject *, QEvent *);
};
#endif // BLOCK_H

block.cpp

#include "block.h"
#include <QPainter>
#include <QtWidgets>
class QGraphicsSceneMouseEvent;
Block::Block(QGraphicsItem *parent)
         : QGraphicsPathItem(parent)
{
QPainterPath p;
//<->,|,<->,|,roundness
p.addRoundedRect(0,0,80,50, 5, 5);
setPath(p);
setAcceptDrops(true);
setAcceptedMouseButtons(Qt::LeftButton);
}
void Block::paint(QPainter *painter, const QStyleOptionGraphicsItem *option, 
QWidget *widget)
{
Q_UNUSED(option)
Q_UNUSED(widget)
painter->setPen(QPen(QColor(67, 141, 220)));
painter->setBrush(QColor(67, 141, 220,100));
painter->drawPath(path());
}

Answer 1

首先，如果要在另一个项目的顶部放置QGraphicsPixmapItem，则更好的选择是将其设置为parentItem。

另一方面，我们可以使用事件过滤器，但是在这种情况下，一个更好的选择是实现自定义QGraphicsScene，在使用左键时，它允许拖动项目，因为我们使用QDrag，然后通过该项目的数据，然后我们覆盖事件dropEvent，我们将获得该项目并建立新的父母。

GraphicsScene.h

#ifndef GRAPHICSSCENE_H
#define GRAPHICSSCENE_H
#include <QGraphicsScene>
class QMenu;
class QAction;
class GraphicsScene : public QGraphicsScene
{
public:
    using QGraphicsScene::QGraphicsScene;
protected:
    void mousePressEvent(QGraphicsSceneMouseEvent *event) override;
    void dropEvent(QGraphicsSceneDragDropEvent *event) override;
private:
    QGraphicsPixmapItem *findPixmapItem(QGraphicsItem *item);
    void createDrag(const QPointF &pos, QWidget *widget, QGraphicsItem *item);
    void showContextMenu(const QPointF &pos);
    void addPixBlock(QGraphicsItem *item);
    QMenu *menu;
    QMenu *submenu;
    QAction *picture;
    QGraphicsPixmapItem *pix;
};
#endif // GRAPHICSSCENE_H

graphicsscene.cpp

#include "graphicsscene.h"
#include <QDrag>
#include <QGraphicsItem>
#include <QGraphicsSceneMouseEvent>
#include <QMenu>
#include <QMimeData>
#include <QWidget>
void GraphicsScene::mousePressEvent(QGraphicsSceneMouseEvent *event)
{
    auto its =  items(QRectF(event->scenePos() - QPointF(1,1), QSize(3,3)));
    auto val = std::find_if(its.constBegin(), its.constEnd(), [](auto const& it){
        return it->type() > QGraphicsItem::UserType;
    });
    if(val == its.constEnd())
        return;
    if(event->button() == Qt::RightButton){
        showContextMenu(event->scenePos());
    }
    else{
        createDrag(event->scenePos(), event->widget(), *val);
    }
}
void GraphicsScene::dropEvent(QGraphicsSceneDragDropEvent *event)
{
    QByteArray byteArray = event->mimeData()->data("Item");
    QGraphicsPixmapItem * item = *reinterpret_cast<QGraphicsPixmapItem**>(byteArray.data());
    QGraphicsItem *item_parent = itemAt(event->scenePos(), QTransform());
    item->setParentItem(item_parent);
}
QGraphicsPixmapItem *GraphicsScene::findPixmapItem(QGraphicsItem *item){
    auto chs = item->childItems();
    auto  val = std::find_if(chs.constBegin(), chs.constEnd(), [](auto const& it){
            return static_cast<QGraphicsPixmapItem *>(it) != Q_NULLPTR;
});
    return val == chs.constEnd() ? Q_NULLPTR : static_cast<QGraphicsPixmapItem *>(*val);
}
void GraphicsScene::createDrag(const QPointF &pos, QWidget *widget, QGraphicsItem *item){
    QGraphicsPixmapItem *pix = findPixmapItem(item);
    if(pix == Q_NULLPTR)
        return;
    QByteArray byteArray(reinterpret_cast<char*>(&pix),sizeof(QGraphicsPixmapItem*));
    QDrag *drag = new QDrag(widget);
    QMimeData * mimeData = new QMimeData;
    mimeData->setData("Item",byteArray);
    drag->setMimeData(mimeData);
    drag->setHotSpot(pos.toPoint()-pix->scenePos().toPoint());
    drag->setPixmap(pix->pixmap());
    drag->start();
}
void GraphicsScene::showContextMenu(const QPointF &pos)
{
    QGraphicsItem *item = itemAt(pos, QTransform());
    menu= new QMenu("Menu");
    submenu = menu->addMenu(QIcon(":/img/pix.png"),"Pix");
    picture = submenu->addAction(QIcon(":/img/pix.png"),"Pix");
    connect(picture, &QAction::triggered, [item, this](){
        addPixBlock(item);
    });
    menu->exec(QCursor::pos());
}
void GraphicsScene::addPixBlock(QGraphicsItem *item)
{
    if(findPixmapItem(item))
        return;
    QPixmap pixmap(":/img/pix.png");
    pix = addPixmap(pixmap.scaled(70,50));
    if(pix->parentItem() != item)
        pix->setParentItem(item);
}

然后我们建立了新场景并添加Blocks。

可以在以下链接