自定义QGraphicsItem和QGraphicsView
- 说明
- 示例
- `myitem.h`
- `myitem.cpp`
- `myview.h`
- `myview.cpp`
- 调用
- `main.cpp`
- 效果
说明
在使用Qt的图形视图框架实现功能时,一般会在其基础上进行自定义功能实现。
如:滚轮对场景的缩放,鼠标拖动场景中的项,以及可以在场景中进行右键操作等。
示例
myitem
为自定义QGraphicsItem,实现了边框、重绘事件、鼠标悬停、按键、右键菜单等功能。
myitem.h
#ifndef MYITEM_H
#define MYITEM_H#include <QGraphicsItem>class MyItem : public QGraphicsItem
{
public:MyItem();// 边框virtual QRectF boundingRect() const override;// 重绘事件virtual void paint(QPainter *painter, const QStyleOptionGraphicsItem *option,QWidget *widget) override;// 设置笔刷inline void setColor(const QColor &color) {brushColor = color;}protected:// 鼠标按下函数,设置被点击的图形项得到焦点,并改变光标外观virtual void keyPressEvent(QKeyEvent *event) override;// 键盘按下函数,判断是不是向下方向键,若是是,则向下移动图形项virtual void mousePressEvent(QGraphicsSceneMouseEvent *event) override;// 悬停事件函数,设置光标外观和提示virtual void hoverEnterEvent(QGraphicsSceneHoverEvent *event) override;// 右键菜单函数,为图形项添加一个右键菜单virtual void contextMenuEvent(QGraphicsSceneContextMenuEvent *event) override;private:QColor brushColor; // 笔刷颜色
};
#endif // MYITEM_H
myitem.cpp
#include "myitem.h"
#include <QPainter>
#include <QCursor>
#include <QKeyEvent>
#include <QGraphicsSceneHoverEvent>
#include <QGraphicsSceneContextMenuEvent>
#include <QMenu>#define WIDTH 40
#define HEIGHT 40#define POS 20MyItem::MyItem()
{brushColor = Qt::black;setFlag(QGraphicsItem::ItemIsFocusable);setFlag(QGraphicsItem::ItemIsMovable);setAcceptHoverEvents(true);}QRectF MyItem::boundingRect() const
{qreal adjust = 0.5; // 返回上下左右+0.5个像素return QRectF(-POS - adjust, -POS - adjust,WIDTH + adjust, HEIGHT + adjust);
}void MyItem::paint(QPainter *painter, const QStyleOptionGraphicsItem *,QWidget *)
{if (hasFocus()) {painter->setPen(QPen(QColor(255, 255, 255)));} else {painter->setPen(QPen(QColor(100, 100, 100)));}painter->setBrush(brushColor);painter->drawRect(-POS, -POS, WIDTH, HEIGHT);
}void MyItem::mousePressEvent(QGraphicsSceneMouseEvent *e)
{setFocus();// 设置光标为手握下的形状setCursor(Qt::ClosedHandCursor);QGraphicsItem::mousePressEvent(e);
}void MyItem::keyPressEvent(QKeyEvent *event)
{if (Qt::Key_Down == event->key())moveBy(0, 10);else if(Qt::Key_Up == event->key())moveBy(0, -10);else if(Qt::Key_Left == event->key())moveBy(-10, 0);else if(Qt::Key_Right == event->key())moveBy(10, 0);else{}QGraphicsItem::keyPressEvent(event);
}void MyItem::hoverEnterEvent(QGraphicsSceneHoverEvent *)
{// 设置光标为手张开的形状setCursor(Qt::OpenHandCursor);setToolTip("click me");
}void MyItem::contextMenuEvent(QGraphicsSceneContextMenuEvent *event)
{QMenu menu;QAction *moveAction = menu.addAction("move origin");QAction *selectedAction = menu.exec(event->screenPos());if (selectedAction == moveAction) {setPos(0, 0);}
}
myview.h
myview
继承QGraphicsView,重新实现了滚轮事件,可对场景进行缩放操作
#ifndef MYVIEW_H
#define MYVIEW_H#include <QObject>
#include <QGraphicsView>class MyView : public QGraphicsView
{Q_OBJECT
public:explicit MyView(QWidget *parent = 0);protected:// 滚轮事件:缩放virtual void wheelEvent(QWheelEvent *event) override;
};
#endif // MYVIEW_H
myview.cpp
#include "myview.h"#include "myview.h"
#include <QKeyEvent>MyView::MyView(QWidget *parent) :QGraphicsView(parent)
{
}void MyView::wheelEvent(QWheelEvent *event)
{if(event->delta() > 0){scale(1.1, 1.1);}else{scale(0.9, 0.9);}// 加上这个,否则在场景和图形项中就没法再接收到该事件了QGraphicsView::wheelEvent(event);
}
调用
main.cpp
#include <QApplication>#include "myitem.h"
#include "myview.h"
#include <QTime>
#include <QtMath>#include <QDebug>int main(int argc, char* argv[ ])
{QApplication app(argc, argv);qsrand(QTime(0, 0, 0).secsTo(QTime::currentTime()));QGraphicsScene scene;// 设置场景尺寸,减少动态渲染scene.setSceneRect(-300, -225, 600, 450);// 创建项for (int i = 0; i < 5; ++i) {MyItem *item = new MyItem;item->setColor(QColor(qrand() % 256, qrand() % 256, qrand() % 256));item->setPos(i * 50 - 100, -50);scene.addItem(item);}// 声明视图MyView view;view.setScene(&scene);// 设置背景刷view.setBackgroundBrush(QBrush(QColor(220, 220, 220)));view.show();return app.exec();
}
效果
显示效果如下:
自定义图形视图