图形项的 QGraphicsScene 内的可拖动像素图

Question

我有一个带有 QGraphicsItems 块的 12*4 网格的场景，当我右键单击这些块时，我有一个上下文菜单可以在块内添加图标我的问题是我不知道如何让这些图标可以拖动到图形场景中的其他块，我知道有 "Draggable Icons Example" 但我怎样才能将该代码实现到图形场景中。

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);
}

block.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，如果您想将 QGraphicsPixmapItem 放在另一个项目之上，更好的选择是将其设置为您的 parentItem。

另一方面，我们可以使用事件过滤器，但在这种情况下更好的选择是实现自定义 QGraphicsScene，当按下左键时，它允许拖动项目，为此我们使用 QDrag 并传递项目的数据，然后我们覆盖事件 dropEvent 我们将在其中获取项目并建立新的父项。

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);
}

然后我们建立新场景并添加 Blocks。

完整的例子可以在下面找到link

图形项的 QGraphicsScene 内的可拖动像素图

Draggable pixmaps inside a QGraphicsScene of graphic items

c++

qt

qgraphicsitem

qt5

qgraphicspixmapitem