看到书上的例子,不知道FlashItem::paint()是如何被调用的，形参中“QPainter *painter”会在重绘时自动被调用吗？代码如下（去掉了其他items只留下flashitem）:
=======pro文件：============================
#-------------------------------------------------
#
# Project created by QtCreator 2013-05-30T14:48:51
#
#-------------------------------------------------
QT += core gui
greaterThan(QT_MAJOR_VERSION, 4): QT += widgets
TARGET = my_GItem
TEMPLATE = app
SOURCES += main.cpp\
mainwindow.cpp \
flashitem.cpp
HEADERS += mainwindow.h \
flashitem.h
=======FLASHITEM_H文件============================
#ifndef FLASHITEM_H
#define FLASHITEM_H
#include <QObject>
#include <QGraphicsItem>
#include <QPainter>
class FlashItem : public QObject,public QGraphicsItem
{
Q_OBJECT
public:
explicit FlashItem(QObject *parent = 0);
QRectF boundingRect() const;
void paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget);
void timerEvent(QTimerEvent *);
private:
bool flash;
QTimer *timer;
signals:
public slots:
};
#endif // FLASHITEM_H
=======MAINWINDOW_H文件：============================
#ifndef MAINWINDOW_H
#define MAINWINDOW_H
#include <QMainWindow>
#include <QGraphicsScene>
#include <QGraphicsView>
#include <QMenuBar>
#include <QGraphicsEllipseItem>
class MainWindow : public QMainWindow
{
Q_OBJECT
public:
MainWindow(QWidget *parent = 0);
~MainWindow();
void initScene(); //初始化场景
//创建主窗体的菜单栏
public slots:
void slotAddFlashItem(); //新建一个显示窗体
private:
QGraphicsScene *scene;
};
#endif // MAINWINDOW_H
=======FLASHITEM_CPP文件：============================
#include "flashitem.h"
FlashItem::FlashItem(QObject *parent) :
QObject(parent)
{
flash=true;
setFlag(ItemIsMovable);
startTimer(1000);
}
QRectF FlashItem::boundingRect() const
{
qreal adjust = 2;
return QRectF(-10-adjust,-10-adjust,43+adjust,43+adjust);
}
void FlashItem::paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget)
{
painter->setPen(Qt::NoPen);
painter->setBrush(Qt::darkGray);
painter->drawEllipse(-7,-7,40,40);
painter->setPen(QPen(Qt::black,0));
painter->setBrush(flash?(Qt::red):(Qt::yellow));
painter->drawEllipse(-10,-10,40,40);
}
void FlashItem::timerEvent(QTimerEvent *)
{
flash=!flash;
update();
}
=======main_CPP文件：============================
#include "mainwindow.h"
#include <QApplication>
int main(int argc, char *argv[])
{
QApplication a(argc, argv);
MainWindow w;
w.show();
return a.exec();
}
=======mainwindow_CPP文件：============================
#include "mainwindow.h"
#include "flashitem.h"
#include <QGraphicsItemAnimation>
#include <QTimeLine>
MainWindow::MainWindow(QWidget *parent)
: QMainWindow(parent)
{
scene = new QGraphicsScene;
scene->setSceneRect(-200,-200,400,400);
initScene(); //初始化场景
QGraphicsView *view = new QGraphicsView;
view->setScene(scene);
view->setMinimumSize(400,400);
view->show();
setCentralWidget(view);
resize(550,450);
setWindowTitle(tr("my_GItems"));
}
MainWindow::~MainWindow()
{
}
void MainWindow::initScene() //初始化场景
{
int i;
for(i=0;i<3;i++)
slotAddFlashItem();
}
void MainWindow::slotAddFlashItem() //在场景中加入一个闪烁图元
{
FlashItem *item = new FlashItem;
scene->addItem(item);
item->setPos((qrand()%int(scene->sceneRect().width()))-200,(qrand()%int(scene->sceneRect().height()))-200);
}
