学以致用，使用设计模式之建造者模式绘制小猪。
代码接口：申明绘制的步骤 PigBuilder.h
#ifndef PIGBUILDER_H#define PIGBUILDER_H#include <QObject>#include <QPainter>class PigBuilder : public QObject{Q_OBJECTpublic:explicit PigBuilder(QObject *parent = nullptr) : QObject(parent){}virtual ~PigBuilder(){}// 绘制身体virtual void drawBody(QPainter &painter) = 0;// 绘制胳膊virtual void drawEars(QPainter &painter) = 0;// 绘制眼睛virtual void drawEyes(QPainter &painter) = 0;// 绘制鼻子virtual void drawNose(QPainter &painter) = 0;// 绘制腿virtual void drawLegs(QPainter &painter) = 0;// 绘制尾巴virtual void drawTail(QPainter &painter) = 0;};#endif // PIGBUILDER_H实例化：实例出具体绘制的小猪 SimplePig
#include "pigbuilder.h"class SimplePig : public PigBuilder{Q_OBJECTpublic:explicit SimplePig(QObject *parent = nullptr) : PigBuilder(parent){}virtual ~SimplePig(){}virtual void drawBody(QPainter &painter){painter.setBrush(QBrush(QColor(247, 204, 148)));painter.setPen(Qt::NoPen);painter.drawEllipse(QPointF(250, 250), 100, 120);}virtual void drawEars(QPainter &painter){painter.setBrush(QBrush(QColor(247, 204, 148)));painter.setPen(Qt::NoPen);painter.drawEllipse(QPointF(200, 180), 40, 50);painter.drawEllipse(QPointF(300, 180), 40, 50);}virtual void drawEyes(QPainter &painter){painter.setBrush(QBrush(QColor(255, 255, 255)));painter.setPen(Qt::NoPen);painter.drawEllipse(QPointF(225, 235), 15, 25);painter.drawEllipse(QPointF(275, 235), 15, 25);painter.setBrush(QBrush(QColor(0, 0, 0)));painter.drawEllipse(QPointF(225, 235), 8, 15);painter.drawEllipse(QPointF(275, 235), 8, 15);}virtual void drawNose(QPainter &painter){painter.setBrush(QBrush(QColor(255, 185, 185)));painter.setPen(Qt::NoPen);painter.drawEllipse(QPointF(250, 270), 15, 20);}virtual void drawLegs(QPainter &painter){painter.setBrush(QBrush(QColor(247, 204, 148)));painter.setPen(Qt::NoPen);painter.drawEllipse(QPointF(200, 320), 20, 40);painter.drawEllipse(QPointF(300, 320), 20, 40);}virtual void drawTail(QPainter &painter){painter.setBrush(QBrush(QColor(247, 204, 148)));painter.setPen(Qt::NoPen);painter.drawEllipse(QPointF(320, 250), 20, 40);}};建造者：用于创建小猪 PigDirector
class PigDirector : public QObject{Q_OBJECTpublic:explicit PigDirector(QObject *parent = nullptr) : QObject(parent){m_pigBuilder = nullptr;}virtual ~PigDirector(){}void setBuilder(PigBuilder *pigBuilder){m_pigBuilder = pigBuilder;}void draw(QPainter &painter){if (m_pigBuilder != nullptr){m_pigBuilder->drawBody(painter);m_pigBuilder->drawEars(painter);m_pigBuilder->drawEyes(painter);m_pigBuilder->drawNose(painter);m_pigBuilder->drawLegs(painter);m_pigBuilder->drawTail(painter);}}private:PigBuilder *m_pigBuilder;};窗体：用于显示 MainWidget
class MainWidget : public QWidget{Q_OBJECTpublic:MainWidget(QWidget *parent = nullptr): QWidget(parent){setFixedSize(500, 500);// 创建简单的小猪PigBuilder *pigBuilder = new SimplePig();// 设置小猪的构建方式m_pigDirector.setBuilder(pigBuilder);}~MainWidget(){}protected:void paintEvent(QPaintEvent *event) override{Q_UNUSED(event);QPainter painter(this);painter.setRenderHint(QPainter::Antialiasing);// 构建并绘制小猪m_pigDirector.draw(painter);}private:PigDirector m_pigDirector;};调用：
#include "mainwindow.h"#include <QApplication>int main(int argc, char *argv[]){QApplication a(argc, argv);MainWidget w;w.show();return a.exec();}
