關于以前的這篇博文，進行補坑

https://blog.csdn.net/qq78442761/article/details/80957186

坑的位置在這，采用上面這篇博文的配法，無法得到圖元在場景中的坐標。

如下圖：

原因是上篇博文，拖拽，是直接從ListWidget脫到場景中的。

而正在要實現的邏輯是，拖到視圖中，然后視圖再往場景放圖元。而且，最好是對拖動的圖像，也自定義下，這是為了重寫，畫圖和邊框的函數，用他自己帶的，可以會出現莫名其妙的現象。

完成后，就可以獲取圖在場景中的坐標了，如下圖所示：

程序結構圖如下：

代碼如下：

mygraphicslineitem.h

#ifndef MYGRAPHICSLINEITEM_H #define MYGRAPHICSLINEITEM_H#include <QGraphicsItem>class MyGraphicsLineItem : public QGraphicsItem { public:MyGraphicsLineItem();~MyGraphicsLineItem();QRectF boundingRect()const;void paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget); };#endif // MYGRAPHICSLINEITEM_H

mygraphicsrectitem.h

#ifndef MYGRAPHICSRECTITEM_H #define MYGRAPHICSRECTITEM_H#include <QGraphicsItem>class MyGraphicsRectItem : public QGraphicsItem { public:MyGraphicsRectItem();~MyGraphicsRectItem();QRectF boundingRect()const;void paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget); };#endif // MYGRAPHICSRECTITEM_H

mygraphicsscene.h

#ifndef MYGRAPHICSSCENE_H #define MYGRAPHICSSCENE_H#include <QObject> #include <QGraphicsView> class MyGraphicsScene : public QGraphicsScene {Q_OBJECT public:MyGraphicsScene(QWidget *parent=0);~MyGraphicsScene();void createRect(const QPointF &pt);void createLine(const QPointF &pt);protected:void dragEnterEvent(QGraphicsSceneDragDropEvent *event);void dropEvent(QGraphicsSceneDragDropEvent* event);void dragMoveEvent(QGraphicsSceneDragDropEvent *event);private:QGraphicsScene *m_scene; };#endif // MYGRAPHICSSCENE_H

mygraphicsview.h

#ifndef MYGRAPHICSVIEW_H #define MYGRAPHICSVIEW_H#include <QObject> #include <QGraphicsView>class MyGraphicsView : public QGraphicsView { public:MyGraphicsView(QWidget *parent=0);~MyGraphicsView();protected:void dragEnterEvent(QDragEnterEvent *event);void dropEvent(QDropEvent *event);};#endif // MYGRAPHICSVIEW_H

mylistwidget.h

#ifndef MYLISTWIDGET_H #define MYLISTWIDGET_H#include <QObject> #include <QListWidget>class MyListWidget:public QListWidget {Q_OBJECT public:MyListWidget(QWidget *parent=0);~MyListWidget();protected:void mouseMoveEvent(QMouseEvent *event);void mousePressEvent(QMouseEvent *event);private:QPoint m_dragPosition; // 拖放起點QListWidgetItem *m_dragItem; // 被拖放的item };#endif // MYLISTWIDGET_H

widget.h

#ifndef WIDGET_H #define WIDGET_H#include <QWidget>class MyGraphicsScene;namespace Ui { class Widget; }class Widget : public QWidget {Q_OBJECTpublic:explicit Widget(QWidget *parent = 0);~Widget();public slots:void printBtnClicked();private:Ui::Widget *ui;MyGraphicsScene *m_scene; };

main.cpp

#include "widget.h" #include <QApplication>int main(int argc, char *argv[]) {QApplication a(argc, argv);Widget w;w.show();return a.exec(); }

mygraphicslineitem.cpp

#include "mygraphicslineitem.h" #include <QPainter> #include <QBrush>MyGraphicsLineItem::MyGraphicsLineItem() {}MyGraphicsLineItem::~MyGraphicsLineItem() {}QRectF MyGraphicsLineItem::boundingRect() const {qreal penWidth=1;return QRectF(0-penWidth/2,0-penWidth/2,4+penWidth,80+penWidth); }void MyGraphicsLineItem::paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget) {Q_UNUSED(option)Q_UNUSED(widget)painter->setBrush(Qt::red);painter->drawRect(0,0,4,80); }

mygraphicsrectitem.cpp

#include "mygraphicsrectitem.h" #include <QPainter> #include <QDebug> #include <QBrush>MyGraphicsRectItem::MyGraphicsRectItem() {}MyGraphicsRectItem::~MyGraphicsRectItem() {}QRectF MyGraphicsRectItem::boundingRect() const {qreal penWidth=1;return QRectF(0-penWidth/2,0-penWidth/2,18+penWidth,56+penWidth); }void MyGraphicsRectItem::paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget) {Q_UNUSED(option)Q_UNUSED(widget)painter->setBrush(Qt::red);painter->drawRect(0,0,18,56); }

mygraphicsscene.cpp

#include "mygraphicsscene.h" #include <QDebug> #include <QMimeData> #include <QGraphicsSceneDragDropEvent> #include <QGraphicsLineItem> #include <QGraphicsRectItem> #include <QGraphicsScene> #include <QPen> #include "mygraphicslineitem.h" #include "mygraphicsrectitem.h"MyGraphicsScene::MyGraphicsScene(QWidget *parent):QGraphicsScene(parent) {}MyGraphicsScene::~MyGraphicsScene() {}void MyGraphicsScene::createRect(const QPointF &pt) {MyGraphicsRectItem *item=new MyGraphicsRectItem;item->setPos(pt);item->setFlags(QGraphicsItem::ItemIsSelectable|QGraphicsItem::ItemIsMovable);addItem(item); }void MyGraphicsScene::createLine(const QPointF &pt) {MyGraphicsLineItem *item=new MyGraphicsLineItem;item->setPos(pt);item->setFlags(QGraphicsItem::ItemIsSelectable|QGraphicsItem::ItemIsMovable);addItem(item); }void MyGraphicsScene::dragEnterEvent(QGraphicsSceneDragDropEvent *event) {if(event->mimeData()->hasFormat("text/plain")){event->acceptProposedAction();} }void MyGraphicsScene::dropEvent(QGraphicsSceneDragDropEvent *event) {QGraphicsScene::dropEvent(event); }void MyGraphicsScene::dragMoveEvent(QGraphicsSceneDragDropEvent *event) {event->accept(); }

mygraphicsview.cpp

#include "mygraphicsview.h" #include "mygraphicsscene.h"#include <QDragEnterEvent> #include <QMimeData> #include <QDebug>MyGraphicsView::MyGraphicsView(QWidget *parent):QGraphicsView(parent) {}MyGraphicsView::~MyGraphicsView() {}void MyGraphicsView::dragEnterEvent(QDragEnterEvent *event) {if(event->mimeData()->hasFormat("text/plain")){event->acceptProposedAction();}QGraphicsView::dragEnterEvent(event); }void MyGraphicsView::dropEvent(QDropEvent *event) {if (event->mimeData()->hasFormat("text/plain")){QString text=event->mimeData()->text();MyGraphicsScene *scene=(MyGraphicsScene*)this->scene();if(text=="直線"){scene->createLine(mapToScene(event->pos()));}else if(text=="矩形"){scene->createRect(mapToScene(event->pos()));}else{}event->acceptProposedAction();}QGraphicsView::dropEvent(event); }

mylistWidget.cpp

#include "mylistwidget.h"#include <QMouseEvent> #include <QListWidgetItem> #include <QDrag> #include <QApplication> #include <QMimeData> #include <QPainter> #include <QPixmap>MyListWidget::MyListWidget(QWidget *parent):QListWidget(parent) {}MyListWidget::~MyListWidget(){}void MyListWidget::mouseMoveEvent(QMouseEvent *event){if(!(event->buttons()&Qt::LeftButton))return;if((event->pos()-m_dragPosition).manhattanLength()<QApplication::startDragDistance())return;if(!m_dragItem)return;QDrag *drag=new QDrag(this);QMimeData *mimeData=new QMimeData;mimeData->setText(currentItem()->text());drag->setMimeData(mimeData);if(mimeData->text()=="矩形"){QPixmap dragImg(18,50);QPainter painter(&dragImg);painter.setBrush(QBrush(Qt::red));painter.drawRect(0,0,18,50);drag->setPixmap(dragImg);}else if(mimeData->text()=="直線"){QPixmap dragImg(2,56);QPainter painter(&dragImg);painter.setPen(QPen(Qt::red,2));painter.drawLine(0,0,0,56);drag->setPixmap(dragImg);}else{}drag->exec(Qt::CopyAction|Qt::MoveAction); }void MyListWidget::mousePressEvent(QMouseEvent *event){m_dragPosition=event->pos();m_dragItem=this->itemAt(event->pos());//保持父類繼承下來的按鍵行為QListWidget::mousePressEvent(event); }

widget.cpp

#include "widget.h" #include "ui_widget.h" #include "mygraphicsscene.h"#include <QDebug> #include <QGraphicsItem> #include <QList>Widget::Widget(QWidget *parent) :QWidget(parent),ui(new Ui::Widget) {ui->setupUi(this);this->setWindowTitle("CSDN IT1995");QStringList strList;strList.append("矩形");strList.append("直線");ui->listWidget->insertItems(0,strList);ui->listWidget->setDragEnabled(true);m_scene=new MyGraphicsScene;ui->graphicsView->setScene(m_scene);connect(ui->printPushButton,&QPushButton::clicked,this,&Widget::printBtnClicked);}Widget::~Widget() {delete ui; }void Widget::printBtnClicked() {QList<QGraphicsItem*>listItem=m_scene->items();for(int i=0;i<listItem.size();i++){qDebug()<<"scenePos:"<<listItem[i]->scenePos();} }

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